"Carbon and it's componds"

Carbon and its Compound

1. The earth's crust, has only 0.02% carbon in the form of minerals like carbonates bicarbonates, coal, and petroleum).

2. The atmosphere has 0.03% of carbon dioxide.

3. Inspite of its small amount available in nature ,carbon is a versatile elements as it forms the basis for all living organisms and many things which we use

4. Bonding in carbon:

(a) Atomic number of carbon 6

b) Electronic configuration has 2 electrons in K shell and 4 electrons in shell .

In order to attain the noble gas configuration, carbon should either gain 4 electrons or lose 4 electrons or can share it's 4 electrons with some other element

Gain of 4 electrons (to form octet, i.e. 8 electrons in Canion) is difficult because then a nucleus with 6 protons will have to hold extra four electrons e-) 

Loss of 4 electrons (to attain duplet, ie, 2 electrons like He atom in C4+ cations ) is difficult as it requires large amount of energy to remove four electrons .

Carbon, hence, overcomes this difficulty by sharing it's four valence electrons with other atoms of carbon or with atoms of other elements.

These electrons contributed by the atoms for mutual sharing in order to acquire the stable noble gas configuration is called covalency of that atom. Hence, carbon shows TETRACOVALENCY.

The simplest molecule formed by sharing of electrons (covalent bonds) can be represented by electron dot structure.

Fig. 1.1 Electron dot structure for methane (CH4)

5. Allotropes of carbon: The phenomenon by means of which an element can exist in two or more forms, with similar chemical properties but different physical properties is called allotropy and the different forms are called allotropes Carbon shows the allotropic forms: 1. Diamond ,2. Graphite,3. Fullerenes

 Note:- 

» Diamond is the hardest substance whereas graphite is very soft.

» Diamond is used for grinding and polishing of hard materials and graphite is used as a lubricant.

Diamond has three dimensional rigid structure but graphite has hexagonal sheet layer structure.

» Diamond is a bad conductor of electricity but graphite is very good conductor of electricity.

6. Fullerenes: A new category of carbon allotrope, fullerenes are spherical in shape or a soccer ball like. The first fullerene identified was C-60 with 60 carbon atoms arranged like the godesic dome designed by US architect, Buckminster Fuller, hence these are also known as Buckminster Fullerenes or Bucky Ball structures.

7. Cause of versatile nature of carbon : Four main reasons for versatile nature of carbon are:

(a) Catenation: It is the unique property of self linkage of carbon atoms by means of covalent bonds to form straight chains, or branched chains, or the rings of  sizes (as shown below):

(b)Tetracovalency: Due to small size, and presence of four valence electrons, carbon can form four strong bonds with other carbon atoms, hydrogen, oxygen nitrogen, or sulphur, etc. For example, compounds of carbon with hydrogen are called hydrocarbons.

(c) Multiple Bond Formation: Small size of carbon also enables it to form multiple bonds, (ie, double bonds or triple bonds) with other elements as well as with its own atoms. This increases the number of carbon compounds.

 Note:

» Compounds of carbon with double bonds and triple bonds are called as unsaturated compounds while those with carbon-carbon single bonds are called saturated compounds.

» Alkenes (with -C=C-) and Alkynes are hence unsaturated, whereas Alkanes (with-C-C-) are saturated compounds.

(d) Isomerism: The phenomenon by means of which the carbon compounds with same molecular formula show different structures, and properties, eg. A chain of 4 carbon atoms can be written in two ways.

Hence, number of carbon compounds increases to a huge number.

Ques:- Draw the electron dot structure for O2, CO2, H2O, N2, H2 ,C2H2.

8. Hydrocarbons: Large number of hydrocarbons can be classified as:

Note: In open chain, the name of parent chain is derived from the root word and suffix ane, ene or yne is added depending on the type of bond present in a chain

Table 1. Root word used for naming any compound.

Table 2. General formula and suffix used for alkanes, alkenes and alkynes.

Important: No alkene or alkyne is possible with single carbon atom because double or triple bond is not possible between carbon and hydrogen atom. It is only between two carbon atoms.

9. Functional Group:

• An atom or a group of atoms which when present in a compound gives specific properties to it, is called a functional group
• A single line shown along with a functional group is called as its free valency by which it gets attached to a compound by replacing one hydrogen atom or atoms,
• Functional group replacing the hydrogen is also called as heteroatom because it is different from carbon, and can be nitrogen sulphur, or halogen, etc.

Important: Replacement of hydrogen atom by a functional group is always in such a manner that valency of carbon remains satisfied

Table 3. Some functional groups in carbon compounds.

Note: Cl is named as prefix Chloro, Br as Bromo NH2 as Amino and NO2 as Nitro. Important Note: Symbol R " in a formula represents an Alkyl Group which is formed by the removal of one hydrogen atom from an alkane.

10. Homologous series: A series of organic compounds in which every succeeding member differs from the previous one by -CH2 group or 14 amu 

Note: As the molecular mass increases in a series, so physical properties of the compounds show a variation, but chemical properties which are determined solely by a functional group, remains same within a series

11. Nomenclature of Organic Compounds

(I) Trivial or common names: These names were given after the source from which the organic compounds were first isolated, eg. If a compound has one carbon atom, then its common name will have root word form and so on (see table 4).

Table 4. Root word used for writing trivial or common names.

(II)IUPAC name: International Union of Pure and Applied Chemistry gave following rules for naming various compounds

• (I) Identify the number of carbon atoms and write the word root corresponding to it. eg, if number of carbon atoms are three, then word root is prop .
•  (ii) Presence of a functional group is indicated by prefix or suffix as given in table 2 and table 3.
• (iii)If the name of functional group is to be given as a suffix, the last letter 'e' in the name of compound is deleted and suffix is added,eg, ketone with three carbon atoms is named as: Propane-e-Propan 'one- Propanone.
• Alcohol with three carbons is propanol
• Carboxylic acid with three carbons is propanoic acid. 
•  Halogens, in IUPAC, are written as Prefixes, eg, Compound with two carbons and one chloro group is named as chloroethane (C2H5Cl).

Ques :- Write the structures of the following :-

Methane , Ethane , Propane, Butane ,Ethene, Propene, Butene, Pentene, Ethyne, Propyne, Butyne, Pentyne, Methanol, Ethanol ,Propanol, Methanal, Ethanal,Propanal, Methanoic acid, Ethanoic acid, propanoic acid, Propanone,Butanone,Pentanone.

12 Chemical properties of carbon compounds :

Main properties of carbon compounds are

(a) Combustion Reaction

(b) Oxidation Reaction.

(c)Addition Reaction

(di Substitution Reaction

(a) Combustion Reaction: A chemical reaction in which a substance burns in the presence of air of oxygen is called combustion reaction.

Note: Combustion is always a EXOTHERMIC reaction, eg.

Remember

»Saturated hydrocarbons generally give clean flame whereas unsaturated hydrocarbons give sooty flame (because carbon content is more than hydrogen content in these and hence carbon shows incomplete combustion, and appears as soot).

Saturated hydrocarbons can give sooty flame in limited supply of oxygen 

(b) Oxidation Reaction: The addition of oxygen in a compound upon combustion is called oxidation 

In addition to combustion, oxidation can also be brought about by some substances which are capable of giving oxygen to others, ie, Oxidising agents; e.g. Acidified K2Cr2O7 (Potassium dichromate) and alkaline KMnO4 (Potassium permaganate)

Note:

c) Addition Reaction: Addition of a molecule in unsaturated compounds in the presence of a catalyst, to give saturated compound is called an addition reaction, e.g.

Hydrogenation of vegetable oils as shown in the reaction above

(d) Substitution Reaction: The reactions which involve the replacement of an atom or group of atoms from a molecule by another atom without any change in structure in the remaining part of the molecule

CH4 + Cl2 +hv --> CH3Cl +HCl

13. Ethanol (or alcohol)

Colourless liquid, soluble in water, and has a distinct smell and burning taste. Its consumption in small quantities causes drunkenness and can be lethal.

»Reaction with sodium: With sodium, it gives sodium ethoxide and evolves hydrogen gas.

2CH3CH2OH + 2Na --> 2CH3CH2ONa + H2

»Reaction with conc. H2SO4

CH3CH2OH + concm H2SO4 + heat --> CH2=CH2 + H2O

14 Ethanoic Acid : CH3COOH 

Common Name: Acetic Acid

5-8% solution of aortic acid in water is called Vinegar. And 100% pure acetic acid is called Glacial acetic acid because it has m.pt. 290 K and freezes forming glacier like crystals

Reactions of ethanoic acid: 

Esterification:

Saponification: Esters in the presence of acid or base react to give back alcohol and carboxylic acid this is called saponification. This reaction is used in soap formation.

With base :- 

NaOH + CH3COOH --> CH3COONa  + H2O

With carbonates and bicarbonates: It gives salt, CO2 and water

2CH3COOH + Na2CO3 --> CH3COONa + H2O +CO2

CH3COOH + NaHCO3 --> CH3COONa + H2O +CO2

Soaps and Detergents:

Soaps and Synthetic Detergents: Soaps and detergents are substances used for cleaning Soap: Soaps are sodium or potassium salts of higher fatty acids, such as Oleic acid C17H33COOH), Stearic acid (C17H35COOH), Palmitic acid (C15H31COOH), etc. These acids are present in the form of their esters along with glycerol (an alcohol containing three hydroxyl groups). These esters, called 'glycerides are present in fats and oils of animal and vegetable origin.

Preparation of Soap: When an oil or a fat (glyceride) is treated with sodium hydroxide solution, it gets converted to sodium salt of the acid (soap) and glycerol. The reaction is known as saponification.

Detergents: Chemically, detergents are sodium salts of sulphonic acids, ie, detergents contain a sulphonic acid group (-SO3H), instead of a carboxylic acid group (-COOH), on one end of the hydrocarbon 

Soap molecule = Sodium salts of carboxylic acid

Detergent molecules = sodium salts of sulphonic acid 

Fig. 1.3 Long hydrocarbon chain.

The cleansing action of a detergent is considered to be more effective than a soap

Cleansing Action of Soaps and Detergents: The cleansing action of soaps and detergents follows the same principle.

When a soap or detergent is dissolved in water, the molecules gather together as clusters, called micelles. The tails stick inwards and the heads outwards.

In cleansing the hydrocarbon tail attaches itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. This gives an opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.

NEET previous years Chemistry Q-A

 Class 11

Chapter 4 [Chemical bonding and Molecular structure]

1. Which one of the following sequences represents the correct increasing order of bond angle in the bond angles in the given molecules? 

(a) H2O <OF2<OCl2<ClO2

(b) OCl2<ClO2<H2O<OF2

(c) OF2<H2O<OCl2<ClO2

(d) ClO2<OF2<OCl2<H2O

Ans:- (c) 

Reason:- Water is sp3 hybridised with bond angle 104.5° due to the presence of two lone pairs. OF2 has structure similar to H2O with bond angle 103° due to higher Electronegativity of Fluorine. OCl2 also has similar structure with bond angle 111° because of steric crowding of two chloride atoms. However, ClO2 has π bond character with an odd electron so that bond angle is 118° . 

Class 12

Coordination compounds

1. Which complex compound obeys 18-electron (a) [V(CO)5]  (b) [Fe(NH3)6]2+

(c) [Ni(CO)6] (4) [Mn(H2O)6]2+

Ans:- (b)

Explanation:-(b) The complex which contains 18 valence electrons,follows 18-electron rule.

(a) [V(CO)5]: The number of valence electrons= 5+(2x5)=15e-

(b) [Fe(NH3)6]2+: The number of valence electrons = =6+(6x2)=6+12=18 e-

(c) [Ni(CO)6], : The number of valence electrons=10+(2 × 6)=22 e-

(d) [Mn(H2O)6]2+ : The number of valence electrons=5+(6x2)=17 e-

Thus, only [Fe(NH3)6] follows 18-electron rule.

2.The hybridization, oxidation number of central metal ion and shape of Wilkinson's catalyst are 

(a) dsp2, +1, square planar 

(b) sp3,.  +4, tetrahedral

(c) sp3d, +2, trigonal bipyramidal

(d) d2sp3, +6, octahedral 

Ans:-(a)

Explanation

In Wilkinson's catalyst-(a homogeneous catalyst), (Ph3P)3RhCI, Rh is dsp2 hybridised, has square planar shape and is in +1 oxidation state.

In complex [Rh(Ph3P)3],

 if x= oxidation state of Rh

x+0+(-1)=0

x=+1

3. The oxidation number of S in tetrathionate (S4O6^2-) is 

(a) +5 (b) 0 (c) 2.5 (d) all of these.

Atoms and molecules

 Atoms and Molecules

Introduction:-

Ancient Indian and Greek philosophers have always wondered about the unknown and unseen form of matter.

The idea of divisibility of matter was considered long back in India, around 500 BC. 

An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles.

Ultimately, a stage will come when we shall come across the smallest particles beyond which further division will not be possible.

He named these particles Parmanu. 

Another Indian philosopher, Pakudha Katyayama, elaborated this doctrine and said that these particles normally exist in a combined form which gives us various forms of matter.

Around the same era, ancient Greek philosophers - Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further.

Democritus called these indivisible particles atoms (meaning indivisible).

All this was based on philosophical considerations and not much experimental work to validate these ideas could be done till the eighteenth century.

By the end of the eighteenth century. scientists recognised the difference between elements and compounds and naturally became interested in finding out how and why elements combine and what happens when they combine.

Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.

3.1 Laws of Chemical Combination

The following two laws of chemical combination were established after much experimentations by Lavoisier and Joseph L. Proust.

3.1.1 LAW OF CONSERVATION OF MASS:- 

Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.

3.1.2 LAW OF CONSTANT PROPORTIONS:-

Lavoisier, along with other scientists, noted that many compounds were composed of two or more elements and each such compound had the same elements in the same proportions, irrespective of where the compound came from or who prepared it.

In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 1:8, whatever the source of water.

Thus, if 9 g of water is decomposed. 1 g of hydrogen and 8 g of oxygen are always obtained.

Similarly in ammonia, nitrogen and hydrogen are always present in the ratio 14:3 by mass. whatever the method or the source from which it is obtained.

This led to the law of constant proportions which is also known as the law of definite proportions. 

This law was stated by Proust as "In a chemical substance the elements are always present in definite proportions by mass".

The next problem faced by scientists was to give appropriate explanations of these laws. British chemist John Dalton provided the basic theory about the nature of matter.

Dalton picked up the idea of divisibility of matter, which was till then just a philosophy. He took the name 'atoms' as given by the Greeks and said that the smallest particles of matter are atoms. 

His theory was based on the laws of chemical combination. 

Dalton's atomic theory provided an explanation for the law of conservation of mass and the law of definite proportions.

According to Dalton's atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. 

The postulates of this theory may be stated as follows:

All matter is made of very tiny particles called atoms, which participate in chemical reactions.

Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.

Atoms of a given element are identical in mass and chemical properties.

Atoms of different elements have different masses and chemical properties.

Atoms combine in the ratio of small whole numbers to form compounds

The relative number and kinds of atoms are constant in a given compound.

You will study in the next chapter that all atoms are made up of still smaller particles.

3.2 What is an Atom?

 The building blocks of all matter are atoms.

How big are atoms?

Atoms are very small, they are smaller than anything that we can imagine or compare with. 

More than millions of atoms when stacked would make a layer barely as thick as this sheet of paper.

 If atoms are so insignificant in size, why should we care about them? 

This is because our entire world is made up of atoms. 

We may not be able to see them, but they are there, and constantly affecting whatever we do. 

Through modern techniques, we can now produce magnified images of surfaces of elements showing atoms.

3.2.1 WHAT ARE THE MODERN DAY SYMBOLS OF ATOMS OF DIFFERENT ELEMENTS?

Dalton was the first scientist to use the symbols for elements in a very specific sense. 

When he used a symbol for an element he also meant a definite quantity of that element. that is, one atom of that element.

Berzilius suggested that the symbols of elements be made from one or two letters of the name of the element.

In the beginning, the names of elements were derived from the name of the place where they were found for the first time.

For example, the name copper was taken from Cyprus. 

Some names were taken from specific colours. 

For example, gold was taken from the English word meaning yellow. 

Now-a-days. IUPAC (International Union of Pure and Applied Chemistry)   is an international scientific organisation which approves names of elements, symbols and units. 

Many of the symbols are the first one or two letters of the element's name in English. 

The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase).

For example:-

hydrogen, H 

aluminium, Al and not AL

(ii) cobalt, Co and not CO.

Symbols of some elements are formed from the first letter of the name and a letter appearing later in the name. 

Examples are: (i) chlorine, Cl (ii) zinc, Zn etc.

Other symbols have been taken from the names of elements in Latin, German or Greek. 

For example, the symbol of iron is Fe from its Latin name ferrum, 

sodium is Na from natrium. 

potassium is K from kalium. 

Therefore, each element has a name and a unique chemical symbol.

3.2.2 ATOMIC MASS

The most remarkable concept that Dalton's atomic theory proposed was that of the atomic mass. 

According to him, each element had a characteristic atomic mass. 

The theory could explain the law of constant proportions so well that scientists were prompted to measure the atomic mass of an atom. 

Since determining the mass of an individual atom was a relatively difficult task. 

Relative atomic masses were determined using the laws of chemical combinations and the compounds formed.

Let us take the example of a compound. carbon monoxide (CO) formed by carbon and oxygen. 

It was observed experimentally that 3 g of carbon combines with 4 g of oxygen to form CO. 

In other words, carbon combines with 4/3 times its mass of oxygen. 

Suppose we define the atomic mass unit (earlier abbreviated as 'amu', but according to the latest IUPAC recommendations. 

It is now written as 'u' - unified mass) as equal to the mass of one carbon atom, then we would assign carbon an atomic mass of 1.0 u and oxygen an atomic mass of 1.33 u. 

However, it is more convenient to have these numbers as whole numbers or as near to a whole numbers as possible. 

While searching for various atomic mass units, scientists initially took 1/ 16 of the mass of an atom of naturally occurring oxygen as the unit. 

This was considered relevant due to two reasons: 

oxygen reacted with a large number of elements and formed compounds.

this atomic mass unit gave masses of most of the elements as whole numbers. 

However, in 1961 for a universally accepted atomic mass unit, carbon-12 isotope was chosen as the standard reference for measuring atomic masses. 

One atomic mass unit is a mass unit equal to exactly one-twelfth (1/12) the mass of one atom of carbon-12. 

The relative atomic masses of all elements have been found with respect to an atom of carbon-12.

Imagine a fruit seller selling fruits without any standard weight with him. He takes a watermelon and says, "this has a mass equal to 12 units" (12 watermelon units or 12 fruit mass units). 

He makes twelve equal pieces of the watermelon and finds the mass of each fruit he is selling, relative to the mass of one piece of the watermelon. 

Now he sells his fruits by relative fruit mass unit (amu), as in Fig. 3.4. 

Similarly, the relative atomic mass of the atom of an element is defined as the average  mass of the atom, as compared to 1/12 the mass of one carbon-12 atom.

3.2.3 HOW DO ATOMS EXIST

Atoms are not able to exist independently. 

Atoms form molecules and ions. 

These molecules or ions aggregate in large numbers to form the matter that we can see, feel or touch.

3.3 What is a Molecule?

A molecule is in general a group of two or more atoms that are chemically bonded together, that is, tightly held together by attractive forces. 

A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.

Atoms of the same element or of different elements can join together to form molecules.

3.3.1 MOLECULES OF ELEMENTS

The molecules of an element are constituted by the same type of atoms. 

Molecules of many elements, such as argon (Ar), helium (He) etc. are made up of only one atom of that element.

But this is not the case with most of the non metals. 

For example, 

A molecule of oxygen consists of two atoms of oxygen and hence it is known as a diatomic molecule, O2

If 3 atoms of oxygen unite into a molecule, instead of the usual 2. we get ozone, O3,

 The number of atoms constituting a molecule is known as its atomicity.

Metals and some other elements, such as carbon, do not have a simple structure but consist of a very large and indefinite number of atoms bonded together.

Let us look at the atomicity of some non-metals.

3.3.2 MOLECULES OF COMPOUNDS

Atoms of different elements join together in definite proportions to form molecules of compounds.

Few examples are given in Table 3.4.

3.3.3 WHAT IS AN ION?

Compounds composed of metals and non metals contain charged species. 

The charged species are known as ions. 

lons may consist of a single charged atom or a group of atoms that have a net charge on them. 

An ion can be negatively or positively charged. 

A negatively charged ion is called an 'anion' and 

the positively charged ion, a 'cation. 

Take, for example, sodium chloride (NaCl). Its constituent particles are positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). 

Ions may consist of a single atom or a group of atoms that have a net charge on them.

A group of atoms carrying a charge is known as a polyatomic ion (Table 3.6).

 We shall learn more about the formation of ions in Chapter 4.

3.4 Writing Chemical Formulae

The chemical formula of a compound is a symbolic representation of its composition. 

The chemical formulae of different compounds can be written easily. 

For this exercise, we need to learn the symbols and combining capacity of the elements.

The combining power (or capacity) of an element is known as its valency.

Valency can be used to find out how the atoms of an element will combine with the atom(s) of another element to form a chemical compound. 

The valency of the atom of an element can be thought of as hands or arms of that atom.

Human beings have two arms and an octopus has eight.

 If one octopus has to catch hold of a few people in such a manner that all the eight arms of the octopus and both arms of all the humans are locked, how many humans do you think the octopus can hold?

 Represent the octopus with O and humans with H. 

Can you write a formula for this combination? 

Do you get OH4, as the formula? The subscript 4 indicates the number of humans held by the octopus.

The valencies of some common ions are given in Table 

The rules that you have to follow while writing a chemical formula are as follows:

the valencies or charges on the ion must balance.

when a compound consists of a metal and a non-metal, the name or symbol of the metal is written first. 

For example: calcium oxide (CaO), sodium chloride (NaCl). iron sulphide (FeS), copper oxide (CuO) etc.. where oxygen, chlorine, sulphur are non metals and are written on the right whereaswhereas calcium, sodium, iron and copper are metals, and are written on the left.

in compounds formed with polyatomic ions, the number of ions present in the compound is indicated by enclosing the formula of ion in a bracket and writing the number of ions outside the bracket.

For example, Mg (OH)2. 

In case the number of polyatomic ion is one, the bracket is not required. 

For example, NaOH.

3.4.1 FORMULAE OF SIMPLE COMPOUNDS

While writing the chemical formulae for compounds, we write the constituent elements and their valencies as shown below. 

Then we must crossover the valencies of the combining atoms.

The simplest compounds, which are made up of two different elements are called binary compounds. 

Examples

1. Formula of hydrogen chloride

Symbol :

Valency:

Formula of the compound would be HCl

2. Formula of hydrogen sulphide

Symbol :

Valency :

Formula: H2S

3. Formula of carbon tetrachloride

Symbol 

Valency 

Formula: CCI4

4. Formula of magnesium chloride

Symbol 

Charge

Formula: MgCl2

Note that in the formula, the charges on the ions are not indicated.

Some more examples:- 

Formula for aluminium oxide:

Symbol

Charge

Formula: 

Formula for calcium oxide:

Symbol

Charge

Formula

Here, the valencies of the two elements are the same. 

You may arrive at the formula Ca2O2. 

But we simplify the formula as CaO.

(c) Formula of sodium nitrate:

Symbol

Charge

Formula

(d) Formula of calcium hydroxide:

Symbol

Charge 

Formula

Note that the formula of calcium hydroxide is Ca(OH)2 and not CaOH2. 

We use brackets when we have two or more of the same ions in the formula. 

Here, the bracket around OH with a subscript 2 indicates that there are two hydroxyl (OH) groups joined to one calcium atom. 

In other words, there are two atoms each of oxygen and hydrogen in calcium hydroxide.

(e) Formula of sodium carbonate:

Symbol

Charge

Formula

In the above example, brackets are not needed if there is only one ion present.

(f) Formula of ammonium sulphate:

Symbol 

Charge

Formula: 

3.5 Molecular Mass and Mole Concept

3.5.1 MOLECULAR MASS

The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance.

It is therefore the relative mass of a molecule expressed in atomic mass units (u).

Example 3.1 (a) Calculate the relative molecular mass of water (H2O).

Solution

 (b) Calculate the molecular mass of HNO3

Solution:

3.5.2 FORMULA UNIT MASS

The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound.

Formula unit mass is calculated in the same manner as we calculate the molecular mass.

The only difference is that we use the word formula unit for those substances whose constituent particles are ions. 

For example, sodium chloride as discussed above, has a formula unit NaCl. 

Its formula unit mass can be calculated as

1 x 23+1 x 35.5= 58.5 u

Example 3.2 Calculate the formula unit mass of CaCl2

Solution:-

1. Calculate the molecular masses of H2, O2,  CO2, CH4,  CH3OH.

2. Calculate the formula unit masses of ZnO, Na2O. K2CO3 (given atomic masses of Zn= 65 u , Na = 23 u , K = 39 u,  C= 12 u and O =16u)

3.5.3 MOLE CONCEPT

Take an example of the reaction of hydrogen and oxygen to form water:

H2 + O2 --> 2H2O

The above reaction indicates that

two molecules of hydrogen combine with one molecule of oxygen to form two molecules of water, or

4u of hydrogen molecules combine with 32 u of oxygen molecules to form 36 u of water molecules.

We can infer from the above equation that the quantity of a substance can be characterised by its mass or the number of molecules. 

But, a chemical reaction equation indicates directly the number of atoms or molecules taking part in the reaction. 

Therefore, it is more convenient to refer to the quantity of a substance in terms of the number of its molecules or atoms, rather than their masses. 

So, a new unit "mole" was introduced. 

The mole, symbol mol, is the SI unit of amount of substance. 

One mole contains exactly 6.02214076 x 1023 elementary entities. 

This number is the fixed numerical value of the Avogadro constant Or Avogadro number.

The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities.

 An elementary entity may be an atom, a molecule. an ion, an electron. any other particle or specified group of particles. 

The mole is the amount of substance of a system that contains 6.02214076 x 1023 specified elementary entities. 1 mole (of anything)= 6.022 x 1023 in number.

Besides being related to a number, a mole has one more advantage over a dozen or a gross. 

This advantage is that mass of 1 mole of a particular substance is also fixed.

The mass of 1 mole of a substance is equal to its relative atomic or molecular mass in grams. 

The atomic mass of an element gives us the mass of one atom of that element in atomic mass units (u). 

To get the mass of 1 mole of atom of that element, that is, molar mass, we have to take the same numerical value but change the units from 'u' to 'g.

 Molar mass of atoms is also known as gram atomic mass. 

For example, atomic mass of hydrogen 1u. So, gram atomic mass of hydrogen = 1 g.

1 u hydrogen has only 1 atom of hydrogen and 1 g hydrogen has 1 mole atoms. that is. 6.022 x 10 atoms of hydrogen. Similarly,

16 u oxygen has only 1 atom of oxygen, 16 g oxygen has 1 mole atoms, that is. 6.022 x 10 atoms of oxygen.

To find the gram molecular mass or molar mass of a molecule, we keep the numerical value the same as the molecular mass, but simply change units as above from u to g. For example, as we have already calculated. molecular mass of water (H2O) is 18 u. 

From here we understand that 18 u water has only 1 molecule of water. 18 g water has 1 mole molecules of water, that is, 6.022 x 10 23 molecules of water.

Chemists need the number of atoms and molecules while carrying out reactions, and 

for this they need to relate the mass in grams to the number. It is done as follows:

1 mole = 6.022 x 10" number= Relative mass in grams.

 Thus, a mole is the chemist's counting unit.

The word "mole" was introduced around 1896 by Wilhelm Ostwald who derived the term from the Latin word moles meaning a 'heap' or 'pile. 

A substance may be considered as a heap of atoms or molecules. The unit mole was accepted in 1967 to provide a simple way of reporting a large number- the massive heap of atoms and molecules in a sample.

Example 3.3

1. Calculate the number of moles for the following

(1) 52 g of He 

(2) 12.044 x 10 number of He atoms 

Example 3.4 Calculate the mass of the

following:

(1)0.5 mole of N, gas 

(2) 0.5 mole of N atoms

(3)3.011 x 10 number of N atoms

(4) 6.022 x 1023 number of N molecules 

Example 3.5 Calculate the number of particles in each of the following:

(i)46 g of Na atoms 

(ii) 8 g O2, molecules 

(iii)0.1 mole of carbon atom

Steroids MSc 4th sem

 steroid :- 

introduction :- Steroids constitute a group of structural related organic compounds that are widely distributed both in plants and animals kingdom

Basically steroids are the natural products which are extracted from the nature and can also be synthesised in laboratory .

Steroids have 1,2-cyclopentenophenanthrene nuclei in their structure 

steroid include compounds with wide variation in the structure and and encomposed a variety of components of vital importance to life such as cholesterol, bile acids, vitamin D, sex hormones and antibiotic etc.  

Any compound which gives Diel's hydrocarbon with Se distillation is defined as steroid.

Diel's hydrocarbon:-  Diel's hydrocarbon is a solid with melting point 126 to 127 degree Celsius 

its molecular formula is C18H26

 it was first obtained when steroids are distillated with Se.

 when steroids are distillated at 420 degree Celsius yields, mainly two hydrocarbons crysene and little picene.

 structure of Diel's hydrocarbon was confirmed by its synthesis, starting from 2-(1-nephthyl)-ethyl magnesium bromide and 2,5 dimethyl cyclopentanone.

 Sterols:- sterols are known as steroid alcohol , are a sub group of the steroids and an important class of organic molecules. steroids occur in animals and plant oil and fat . 

 They are crystalline compounds, and contain an alcoholic group they occur free or as ester of higher fatty acids and isolated from unsaponificable portion of oil and fat.

 

 Classification of on the basis of source:- 

 three types

 1. 200 sterols ( animal source )[ cholesterol, cholestanol, Coprosterol]

 2. phytosterols ( plant source)[Campesterol, sitosterol, stigmasterol]

 3.  Mycosterols( yeast and fungi source)[Ergosterol, vitamin D]

 Structure (nucleus and number)

 Gonane also known as steran or cyclopentanoperhydrophenanthrene, the simplest steroid and the nuclear of all steroids and sterols, is composed of C17 atoms in C-C bond forming and four fused ring in a three dimensional shape 

 the three cyclohexane ring A B and C forms the skeleton of perhydroderivative of phenanthrene.

 The D ring has cyclopentane structure .

 When the 2 methyl groups and B,C side chains (at C17) are present, the steroids are said to have cholestane frameworks sterols are forms of steroids with a hydroxyl group at position 3 and a skeletal derived from cholestane .

 All the steroids have this basic nucleus they very in the functional group attached and the side chain attached to these four rings.

 

cholesterol :- 

molecular formula of cholesterol is C27H46O and its melting point is 149 degree Celsius

 this is the sterol of higher animals occurring free or as fatty esters in all animal cells, particularly in the brain and spinal cord. cholesterol was first isolated from human ga stone.

 the main sources of cholesterol are the fish liver oil, the spinal cord of cattles .

 cholesterol is a white crystalline solid which is optically active .

 cholesterol is a waxy substance found normally in blood predominantly produced in liver but alsl found in food such as red meat, high fat cheese , butter eggs etc.

 cholesterol is essential for maintaining the good heart but to high concentration of cholesterol in the blood can leads to high blood pressure, heart disease etc. but good and healthy lifestyle can help to lower cholesterol level and the significant to reduce the risk.

 cholesterol travel in the blood transported in molecules called lipoprotein they are sphere shaped assemblies that keeps the cholesterol separated from the blood.

 There are two types of lipoproteins:-

 1. LDL(low density lipoprotein):;

 It is a bad cholesterol if there is too much LDL in blood it can slowly built in the arteries making them narrower which increases of heart diseases.

 2. high density lipoprotein (HDL):- 

  It is a good cholesterol

  It helps to remove excess cholesterol from the bloodstream and return it to the liver where it is broken down and passed out of the body.

   the structure of cholesterol was elucidated only after a tremendous amount of work particularly by wielard, windairs and their co-workers (1903-1932)

   

   structure determination :- 

   for the elucidation of cholesterol , firstly it is important to know the structure of cholesterol 

   the molecule consists of a side chain and a nucleus composed of four rings . 

   these rings are usually designed A,B,C and D

    it also contains two methyl group at C-10 and C-30

    THE STRUCTURE ELLUSIDATION OF CHOLESTEROL CAN BE DIVIDED INTO FOUR PARTS 

   1 STRUCTURE OF THE RING SYSTEM

   2 POSITION OF HYDROXYL GROUP AND DOUBLE BOND

   3 NATURE AND POSITION OF SIDE CHAIN

   4   POSITION OF 2 ANGULAR METHYL GROUPS

    Structure of the ring system molecular:- Molecular formula of cholesterol is C27H46O

     on acetylation, cholesterol forms monoacetal and this reaction confirms the present of a hydroxy group 

     choesterol is treated with H2 in the presence of catalyst and  with bromine(Br2) it absorbs one mole of H2 and 1 mole of Br2 which indicates the presence of 1 double bond

    Cholesterol shows the following set of reactions:- 

    This leads to the following conclusion:-  

     1 to 2 prove the presence of 1 double bond 

     2 to 3 (a ketone) shows that cholesterol is secondary alcohol 

     3 to 4 cholestane is a saturated hydrocarbon and corresponds to the general formula CnH2n - 6 and hence cholesterol is a tetracyclic compound

      the ring in the steroid nucleus were opened to give a dicarboxylic acid and the relative positions of the two carboxylic groups  with respect to  each other were determined by the application of blanc's  rule :- which states that on heating with acetic anhydride, 1,5 dicarboxylic acids form cyclic anhydride and 1,6 - dicarboxylic acids form cyclopentanones with eliminatiom of CO2. 

ENZYMES MSC 4TH SEM

 Enzymes

• 6.1 An Introduction to Enzymes 183
• 6.2 How Enzymes Work 186
• 6.3 Enzyme Kinetics as an Approach to Understanding mechanism 194
• 64 Examples of Enzymatic Reactions 205 
• 6.5 Regulatory Enzymes 220

Introduction:- 

• There are two fundamental conditions for life.
•  First, the organism must be able to self-replicate; 
• second, it must be able to catalyze chemical reactions efficiently and selectively. 
• The central importance of catalysis may seem surprising, but it is easy to demonstrate. 
• As living systems make use of energy from the environment.
•  Many of them, for example, consume substantial amounts of sucrose-common table sugar as a kind of fuel, usually in the form of sweetened foods and drinks.
•  The conversion of sucrose to CO2, and H₂O in the presence of oxygen is a highly exergonic process, releasing free energy that we can use to think, move, taste and see.
•  However, a bag of sugar can remain on the shelf for years without any obvious conversion to CO₂ and H2O. 
• Although this chemical process is thermodynamically favorable, it is very slow! 
• Yet when sucrose is consumed by a human (or almost any other organism), it releases its chemical energy in seconds. 
• The difference is catalysis. 
• Without catalysis, chemical reactions such as sucrose oxidation could not occur on a useful time scale, and thus could not sustain life.
• In this chapter, then we turn our attention to the reaction catalysts of biological systems: the enzymes, the most remarkable and highly specialized protein. 
• Enzymes have extraordinary catalytic power, often far greater than that of synthetic or inorganic catalysts
• They have a high degree of specificity for their substrates, they accelerate chemical reactions tremendously, and they function in aqueous solutions under very mild conditions of temperature and pH.
•  Few nonbiological catalysts have all these properties. 
• Enzymes are central to every biochemical process. 
• Acting in organized sequences, they catalyze the hundreds of stepwise reactions that degrade nutrient molecules, conserve and transform chemical energy, and make biological macromolecules from simple precursors.

 The study of enzymes has immense practical importance. 

• In some diseases, especially inheritable genetic disorders, there may be a deficiency or even a total absence of one or more enzymes. 
• Other disease conditions may be caused by excessive activity of an enzyme.
•  Measurements of the activities of enzymes in blood plasma, erythrocytes, or tissue samples are important in diagnosing certain illnesses.
•  Many drugs act through interactions with enzymes. 
• Enzymes are also important practical tools in chemical engineering, food technology, and agriculture.
• We begin with descriptions of the properties of enzymes and the principles underlying their catalytic power, then introduce enzyme kineties, a discipline that provides much of the framework for any discussion of enzymes. 
• Specific examples of enzyme mechanisms are then provided, illustrating principles introduced earlier in the chapter. 
• We end with a discussion of how enzyme activity is regulated

6.1 An Introduction to Enzymes

• Much of the history of biochemistry is the history of enzyme research, Biological catalysis was first recognized and described in the late 1700s, in studies on the digestion of meat by secretions of the stomach. 
• Research continued in the 1800s with examinations of the conversion of starch to sugar by saliva and various plant extracts. 
• In the 1850s, Louis Pasteur concluded that fermentation of sugar into alcohol by yeast is catalyzed by "ferments." 
• He postulated that these ferments were in- separable from the structure of living yeast cells; this view, called vitalism, prevailed for decades. 
• Then in 1897 Eduard Buchner discovered that yeast extracts could ferment, sugar to alcohol, proving that fermentation was promoted by molecules that continued to function when removed from cells 
• Buchner's experiment at once marked the end of vitalistic notions and the dawn of the science of biochemistry. 
• Frederick W. Kühne later gave the name enzymes to the molecules detected by Buchner.
• The isolation and crystallization of urease by James Sumner in 1926 was a breakthrough in early enzyme studies.
•  Summer found that urease crystals consisted entirely of protein, and he postulated that all enzymes are proteins. 
• In the absence of other examples, this idea remained controversial for some time.
•  Only in the 1930s was Sumner's conclusion widely accepted, after John Northrop and Moses Kunitz crystallized pepsin, trypsin, and other digestive enzymes and found them also to be proteins.
•  During this period, J. B. S. Haldane wrote a treatise entitled Enzymes.
•  Although the molecular nature of enzymes was not yet fully appreciated, Haldane made the remarkable suggestion that weak bonding interactions between an enzyme and its substrate might be. used to catalyze a reaction.
•  This might lies at the heart of our current understanding of enzymatic catalysis.
• Since the latter part of the twentieth century, thousands of enzymes have been purified, their structures Can elucidated, and their mechanisms explained.

Most Enzymes Are Proteins

With the exception of a small group of catalytic RNA molecules (Chapter 26), all enzymes are proteins. 

Their catalytic activity depends on the integrity of their native protein conformation.

 If an enzyme is denatured or dissociated into its subunits, catalytic activity is usually lost. 

If an enzyme is broken down into its component amino acids, its catalytic activity is always destroyed 

This the primary, secondary, tertiary, and quaternary structures of protein enzymes are essential to their catalytic activity.

Enzymes, like other proteins, have molecular weights ranging from about 12,000 to more than 1 million. 

Some enzymes require no chemical groups for activity other than their amino acid residues.

 Others require an additional chemical component called a cofactor either one or more inorganic ions, such as Fe, Mg, Mr, or Zn (Table 6-1), or a complex organic or metallo organic molecule called a coenzyme. 

Coenzymes act as transient (Table 6-2). 

Most are derived from vitamins, organic nutrients required in small amounts in the diet. 

We consider coenzymes in more detail as we encounter them in the metabolic pathways discussed in Part II 

Some enzymes require both a coenzyme and one or more metal ions for activity. 

A coenzyme or metal ion that is very tightly or even covalently bound to the enzyme protein is called a prosthetic group.

 A complete, catalytically active enzyme together with its bound coenzyme and/or metal ions is called a holoenzyme. 

The protein part of such an enzyme is called the apoenzyme or apoprotein. 

Finally, some enzyme proteins are modified covalently by phosphorylation, glycosylation, and other processes. 

Many of these alterations are involved in the regulation of enzyme activity

Enzymes Are Classified by the Reactions They Catalyze

Many enzymes have been named by adding the suffix "ase" to the name of their substrate or to a word or phrase describing their activity.

 Thus urease catalyzes hydrolysis of urea, and DNA polymerase catalyzes the polymerization of nucleotides to form DNA.

 Other enzymes were named by their discoverers for a broad function, before the specific reaction catalyzed was known, 

For example, an enzyme known to act in the digestion of foods was named pepain, from the Greek pepsis, "digestion." and lysozyme was named for its ability to lyse (break down) bacterial cell walls. 

Still others were named for their source: trypsin, named in part from the Greek trypsin, "to wear down," was obtained by nabbing pancreatic tissue with glycerin. 

Sometimes the same enzyme has two or more names, or two different enzymes have the same name. 

Because of such ambiguities, and the ever-increasing number of newly discovered enzymes, biochemists, by interational agreement, have adopted a system for naming and classifying enzymes 

This system divides enzymes into six classes, each with subclasses, based on the type of reaction catalyzed (Table 6-3). 

Each enzyme is assigned a four-part classification number and a systematic name, which identifies the reaction it, catalyse. 

As an example, the formal systematic name of the enzyme catalyzing the reaction class (phosphotransferase);

 the third number (1), a phosphotransferase with a hydroxyl group as acceptor and the fourth number (1), -glucose as the phosphoryl group acceptor

 For many enzymes, a common name is more frequently used in this case hexokinase.

 A complete list and description of the thousands of known enzymes is maintained by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology

 (www.chem.quid.ac.uk/ibmb/enzyme). 

This chapter is devoted primarily to principles and properties common to all enzymes

SUMMARY 6.1 An Introduction to Enzymes

Life depends on powerful and specific catalysts the enzymes. Almost every biochemical reaction is catalyzed by an enzyme. 

With the exception of a few catalytic RNAs, all known enzymes are proteins. 

Many require nonprotein coenzymes or cofactors for their catalytic function.

ATP D-glucose-ADP+ D-gluse 6-phosphate

is ATP ghase phosphotransferase, which indicates that it catalyzes the transfer of a phosphoryl group from ATP to glucose 

It Ergyme Commission number (E.C. mum. ber) is 2.7.1.1. The first number (2) denotes the class name (transferase); the second number (7), the sub

Enzymes are classified according to the type of reaction they catalyze. All enzymes have formal

E.C. numbers and names, and most have trivial

To understand catalysis, we must first appreciate, the important distinction between reaction equilibria and reaction rates. 

The function of a catalyst is to increase the rate of a reaction.

 Catalysts do not affect reaction equilibria.

 Any reaction, such as SP, can be described by a reaction coordinate diagram (Fig. 6-2), a picture of the energy changes during the reaction. 

As discussed in Chapter 1, energy in biological systems is described in terms of free energy, G. 

In the coordinate diagram, the free energy of the system is plotted against. 

the progress of the reaction (the reaction coordinate). 

The starting point for either the forward or the reverse reaction is called the ground state, the contribution to the free energy of the system by an average molecule (S or P) under a given set of conditions.

AGURE 6-1 inding of a substrate to an mayme at the active site. The enzyme dymotrypsin, with bound substrate in red (PDB ID 70CH Some key activeste amino acid residues appear as a red splotchun the ymme surface.

6.2 How Enzymes Work

The enzymatic catalysis of reactions is essential to living systems, Under biologically relevant conditions, uncatalyzed reactions tend to be slow-most biological molecules are quite stable in the neutral pH, mild temperature, aqueous environment inside cells, Further more, many common chemical processes are unfavorable or unlikely in the cellular environment, such as the transient formation of unstable charged intermediates or the collision of two or more molecules in the precise orientation required for reaction. 

Reactions required to digest food, send nerve signals, or contract a misele simply do not occur at a useful rate without catalysis

An enzyme circumvents these problems by providing a specific environment within which a given reaction can occur more rapidly. 

The distinguishing feature of an enzyme-catalyzed reaction is that it takes place within the confines of a pocket on the enzyme called the active site (Fig. 6-1). 

The molecule that is bound in the active site and acted upon by the enzyme is called the substrate. 

The surface of the active site is lined with amino acid residues with substituent grups that bind the substrate and catalyze its chemical transformation 

Often, the active site encloses a substrate, sequestering it completely from solution.

 The enzyme-substrate complex, whose existence was first proposed by Charles Adolphe Wurtz in 1880, is central to the action of enzymes. 

It is also the starting point for mathematical treatments that define the kinetic behaviour of enzyme catalyzed reactions and for theoretical descriptions of enzyme mechanisms.

Enzymes Affect Reaction Rates, Not Equilibria

A simple enzymatic reaction might be written

KEY CONVENTION: 

To describe the free-energy changes for reactions, chemists define a standand set of conditions (temperature 208 K; partial pressure of each gas 1 atm, or 101.3 kPa concentration of each solute I s) and express the free energy change for a reacting system under these conditions as AG", the standard free-energy change. 

Because biochemical systems commonly involve H concentrations far below 1 M, biochemists define a biochemical standard free-energy change, ∆G, the standard free-energy change at pH 7.0, we employ this definition throughout the book.    

The equilibrium between S and P reflects the difference in the free energies of their ground states. 

In the example shown in Figure 6-2, the free energy of the ground state of P is lower than that of S, so AG for the reaction is negative and the equilibrium favors P. 

The position and direction of equilibrium are not affected by any catalyst.

187

the appropriate enzyme is present, because the rate of the reaction is increased. This general principle is illustrated in the conver sion of sucrose and oxygen to carbon dioxide and water:

A favorable equilibrium does not mean that the SP conversion will occur at a detectable rate. The rate of a reaction is dependent on an entirely different parameter. There is an energy barrier between S and P the energy required for alignment of reacting groups, formation of transient unstable charges, bond re arrangements, and other transformations required for the reaction to proceed in either direction. This is illus trated by the energy "hill" in Figures 6-2 and 6-3, Tb undergo reaction, the molecules must overcome this barrier and therefore must be raised to a higher energy level. At the top of the energy hill is a point at which de cay to the S or P state is equally probable (it is downhill either way). This is called the transition state. The transition state is not a chemical species with any signif icant stability and should not be confused with a reac tion intermediate (such as ES or EP). It is simply a fleeting molecular moment in which events such as bond breakage, band formation, and charge development have proceeded to the precise point at which decay to either substrate or product is equally likely. The stiffer ence between the energy levels of the ground state and the transition state is the activation energy AG The rate of a reaction reflects this activation energy: a higher activation energy corresponds to a slower reaction Reaction rates can be increased by mising the tempera ture and/or pressure, thereby increasing the number of molecules with sufficient energy to overcome the energy barrier. Alternatively, the activation energy can be low ered by adding a catalyst (Fig. 6-3). Catalysts enhance maction rates by lowering activation energies

Enzymes are no exception to the rule that catalysts do not affect reaction equilibria. The bidirectional ar rows in Equation 6-1 nuke this point: any enzyme that catalyzes the reaction S-P also catalyzes the reaction PS. The role of enzymes is to accelerate the inter conversion of Sand P. The enzyme is not used up in the process, and the equilibrium point is unaffected. How ever, the reaction reaches equilibrium much faster when

Transition state (1) A

اد

Reaction coordinate

FIGURE 6-3 Reaction coordinate diagram comparing enzyme

catalyzed and uncatalyzed reactions in the reactions→P the 15 and EP intermediates occipy mnima in the energy progress curve of the enzyme-catalyzed reaction. The tems AG and AC comespond to the activation energy ker the uncatalyad reaction and the overall activation ausgy for the catalyzed seactkin, respectively. The atha bon energy is lowerwhen the enzyme catalyzes the reaction

CulO 120, 1200, +11H₂O

This conversion, which takes place through a series of separate reactions, has a very large and negative AG and at equilibrium the amount of sucrose present is neg ligible. Yet sucrose is a stable compound, because the activation energy barrier that must be overcome before. sucrose reacts with oxygen is quite high. Sucrose can be red in a container with oxygen almost indefinitely without reacting. In cells, however, sucrose is readily broken down to CO, and HO in a series of reactions cal alyzed by enzymes. These enzymes not only accelerate the reactions, they organize and control them so that much of the energy released is recovered in other chem ical forms and made available to the cell for other tasks, The reaction pathway by which sucrose (and other sug ars) is broken down is the primary energy-yielding path way for cells, and the enzymes of this pathway allow the reaction sequence to proceed on a biologically useful time scale

Any reaction may have several steps, involving the formation and decay of transient chemical species called reaction intermediates A reaction intermediate is any species on the reaction pathway that has a finite. chemical lifetime (longer than a molecular vibration, -10 seconds). When the SP reaction is catalyzed i by an enzyme, the ES and EP complexes can be consid ered intermediates, even though S and P are stable chemical species (Ean 6-1); the ES and EP complexes occupy valleys in the reaction coordinate diagram (Fig. 6-3). Additional, less stable chemical intermediates of ten exist in the course of an eryme-catalyzed reaction. The interconversion of two sequential reaction interme diates thus constitutes a reaction step. When several steps occur in a reaction, the overall rate is determined by the step (or steps) with the highest activation en ergy, this is called the rate-limiting step in a simple case, the rate limiting step is the highest-energy point in the diagram for interconversion of S and P. In practice, the tate-limiting step can vary with reaction conditions, and for many enzymes several steps may have similar activation energies, which means they are all partially mate-limiting.

Activation energies are energy barriers to chemical reactions. These barriers are crucial to life itself. The rate - at which a molecule undergoes a particular reaction

In this chapter, lediterinerler to chemical species in the main pathway of a side eye-cataly reaction. In the c it of mutable pothwaysinlingmay ays (discussed in Part II), these term ured somewhat diffently. An entire uzymatic mation often referred to as a step in a pathway, and the prodad cainis (which is the sidstnite for the next eve in the pathway) is referred to an intermediate

" Hereditary and evolution" class 10th

 Topics to be covered

• Introduction
• What is Heredity?
• Inherited traits
• Mendel's experiments
• Laws of Inheritance
• Sex determination
• Evolution
• - Variations & its relation to Evolution
• Acquired vs. Inherited traits
• - Speciation
• -Evolution by stages
• Human evolution

What is Heredity?

• Passing of traits from parents/ancestors to offspring
• Genetics :- The branch of science which deal with the study of heredity

Heredity vs. Inheritance

Heredity

• The process by which characters are transferred from one generation to the next generation is called inheritance / heredity 
• The differences in traits of individuals of a progeny from each other and from their parents are called variations
• The branch of science which deals with inheritance and variation is called genetics

Inherited trait:

A trait that is genetically passed down from one generation to another

Inherited traits: Examples

Hair colour

. Eye colour

. Height

Shape of feet

. Ear lobes

How do the traits get inherited?

1. Mendel's Experiment

• Gregor Johann Mendel (1822-1884) is known as 'Father of Genetics'.
• Mendel performed his experiments with garden pea plant (Pisum sativum)
• He conducted artificial pollination/cross-pollination experiments using several true-breeding varieties having contrasting traits 
• He observed one trait at a time
• He hybridised plants with alternate forms of a single trait (Monohybrid cross). The seeds thus produced were grown to develop into plants of first filial generation (F₁) 
• Mendel then self-pollinated the F, plants to generate plants of second filial generation (F₂)
• Later, Mendel also crossed pea plants that differed in two characters (Dihybrid cross)

2. Mendel's Experimental Plant

Mendel selected garden pea as his experimental material because of the following reasons.

(1) It is an annual plant with a short life-cycle. So, several generations can be studied within a short period.

(2) It has perfect bisexual flowers containing both male and female parts

(3) The flowers are predominantly self-pollmating It is easy to get pure line for several generations.

(4) It is easy to cross-pollmate them because pollens from one plant can be introduced to the stigma of another plant by removing the anthers

(5) Pea plant produces a large number of seeds in one generation

(6) Pea plants could easily be raised, maintained and handled

 (7) A number of easily detectable contrasting characterstraits were available

3. Mendel's Observations

(1) F1 progenies always resembled one of the parents and trait of other parent was not seen

(2) F2 stage expressed both the parental traits in the proportion 3.1.

(3) The contrasting traits did not show any blending at either F1or F2 stage.

 (4) In dihybrid cross, he got identical results as in monohybrid cross

(5) He found that the phenotypes in F2 generation appeared in the ratio 3:1

(6) He found that the genotypic ration in F2 generation appeared in the ratio 1:2:1

4. Mendel's Laws of Inheritance

■ Based on his hybridisation experiments, Mendel proposed the laws of inheritance.

(i) Law of dominance (First law)

■ This law states that when two alternative forms alleles are present in an organism, only one factor expresses itself in F1 progeny and is called dominant while the other that remains masked is called recessive.

(ii) Law of segregation (Second law)

■ This law states that alleles of a pair segregate from each other during gamete formation, such that a gamete receives only one of the two factors. They do not show any blending.

iii) Law of independent assortment

According to this law the two factors of each character separate out independent of the factors of other characters at the time of gamete formation and get randomly rearranged in the offsprings producing both parental and new combinations of characters.

Sex Determination Mechanism :- 

Finalisation of sex at the time of zygote formation is called sex Determination .

XX-XY type :- 

Seen in many insects including humans .

Males have X and Y chromosomes along with autosomes and female have a pair of X chromosomes.

"Magnetic effect of electric current" class 10

 Topics to be covered:- 

• History of magnetism 
• Bar magnet 
• Magnety field
• Operated 's experiment 
• Magnetic field lines
• Magnetic field due to current carrying conductor due to magnetic field
• Electric motor 
• Electromagnetic induction
• Electric generator

Introduction:-

• Nail  attracted towards magnet.
• Refrigerator locked due to magnetic properties
• Metro doors use magnetism
• Electric motors and generators works on magnetism

Story of magnetism:- 

• Shepherd found some rocks that was attracted nail.
• People thought that rocks were magical and so called those rocks magnesia (word from magic)
• Later scientists give it a name magnetism.

Bar magnet:-

• Rectangular object that has a magnetic field .

Properties of bar magnet:-

• Align itself in the north south direction when suspended freely.
• North and South pole cannot be isolated.
• Like led repel and unlike poles attract .

• Not all materials are attracted by magnet.

Magnetic field::

• Region around a magnet where the magnet exerts its influence.

Magnetic field lines:- 

• Magnetic field is a vector quantity [magnitude + direction]
• Visual realization of magnetic field by bar magnet and iron filling experiment.
• Directions:- outside magnet:- North to South and Inside magnet:- South to North

Properties of magnetic field lines :-

• Form continuous closed loops
•  Tangent to magnetic field line at a given point specifies the direction of net magnetic field at that point
• Greater number of magnetic field lines per unit area stronger the magnetic field .
• Two magnetic field lines never intersect each other . If they do so that means it shows two directions at one point which is not possible. 

Operated experiment:- 

• Electricity and magnetism are very closely related .
• Operated observed the inter relation between electricity and magnetism.

Oersted experiment:- 

Observations:- 

• Magnetic compass needle deflected when current passes through a wire.
• A wire carrying electric current behave like a magnet.
• Deflection reverses as the direction of current is reversed.

Conclusion:- 

• A wire carrying electric current behave like a magnet.
• Moving charges produce a magnetic field in the surrounding region.

Magnetic field due to a current carrying 

• Straight conductor 
• Circular loop
• Solenoid

Magnetic field due to a current carrying straight conductor:-

• Magnitude of magnetic field produced at a given point increases as the current through the wire increases. 
• Magnetic field produced by a given current in a conductor decreases as the distance of the point from it increases.

Pattern of field lines:- 

• Concentric circles represent magnetic field around a current carrying straight wire.

Directions of magnetic field:- 

Right hand thumb rule :- If a current carrying straight conductor is held in your right hand such that thumb point towards the direction of current, then the wrapped fingers show direction of magnetic field lines.

Magnetic field due to a current carrying circular loop:-

• Every point on the wire carrying current would give rise to magnetic field appearing as straight lines at the centre of loop 

So

•  magnetic field is directly proportional to current 
• magnetic field is directly proportional to number of turns ,
• magnetic field is inversely proportional to square of distance 

Strength of magnetic field at the centre of coil (loop) depends upon:- 

Radius of coil:-

• Strength of magnetic field is inversely proportional to radius of coil . If radius increases, magnetic strength at the centre decreases.

Number of turns in the coil:- 

• As the number of turns in the coil increases , the magnetic field strength at the centre increases. This is because current in each circular turn is having the same direction thus field due to each turn add up .

The strength of current flowing in the coil:- 

• As the strength increases, the strength of magnetic field increases.

Maxwell Corkscrew Rule/ Right Hand rule:-

•  If we considered ourselves driving a corkscrew in the direction of current, then the direction of corkscrew is the direction of magnetic field.

Magnetic field due to a current carrying solenoid :-

• Solenoid is a coil wound into a tightly packed helix .
• Or 
• A coil of many circular turns of insulated copper wire wrapped in shape of cylinder.
• Field lines of a solenoid are similar to those of bar magnet.
• Field is uniform inside the solenoid.
• Strength of magnetic field is proportional to number of turns and magnitude of current.

Where do we use solenoid:- 

• Transformer creation

Electromagnet:- 

• Strong magnetic field produced inside the solenoid is used to magnetize the magnetic material like steel , soft iron , when placed inside the coil 

Magnetic field :- 

• Introduction of force due to magnetic field:- 
• A current carrying rod experiences a force perpendicular to its length and magnetic field 
• Direction of the force on the conductor depends upon:-
• - Direction of current and 
• - Directions of magnetic field

Fleming Left hand rule:-

Stretch your thumb , forefinger and middle finger of your left hand in such a way that they are mutually perpendicular to each other. If the first finger shows the direction of magnetic field and middle finger show the direction of current then the thumb will show the direction of motion of conductor.

Fleming ' left hand rule demonstration:- 

A relationship between direction of magnetic field, current and the force on the conductor .

Note :- downward :- inward

Upward:- outward

Application:- magnetic field and force exerted by it:- 

• Electric motor ,
• Electric generator
• Loudspeaker,
• Microphone,
• Measuring instruments etc.

Magnetism in medicine

• An electric current always produces a magnetic field. 
• Even weak ion currents that travel along the nerve cells in our body produce magnetic fields. 
• When we touch something, our nerves carry an electric impulse to the muscles we need to use. 
• This impulse produces a temporary magnetic field.
•  These fields are very weak and are about one-billionth of the earth's magnetic field. 
• Two main organs in the human body where the magnetic field produced is significant, are the heart and the brain. 
• The magnetic field inside the body forms the basis of obtaining the images of different body parts.
•  This is done using a technique called Magnetic Resonance Imaging (MRI). 
• Analysis of these images helps in medical diagnosis. 

• Magnetism has, thus got important uses in medicine.

ELECTRIC MOTOR

An electric motor is a rotating device that converts electrical energy to mechanical energy,

 Electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players etc. 

Material requirements:- 

Rectangular coil, magnetic poles , split rings. Axle, brushes and source battery.

Construction:-

An electric motor,  consists of a rectangular coil ABCD of insulated copper wire. 

The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. 

The ends of the coil are connected to the two halves P and Q of a split ring. 

The inner sides of these halves are insulated and attached to an axle. 

The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively, 

Working of electric motor:- 

Current in the coil ABCD enters from the Source battery through conducting brush X and flows back to the battery through brush Y. 

 current in arm AB of the coil flows from A to B. 

In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB.

 On applying Fleming's left hand rule for the direction of force on a current-carrying conductor in a magnetic field .

 We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. 

Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. 

After half rotation. Q makes contact with the brush X and P with brush Y. 

Therefore the current in the coil gets reversed and flows along the path DCBA. 

A device that reverses the direction of flow of current through a circuit is called a commutator. 

In electric motors, the split ring acts as a commutator. 

The reversal of current also reverses the direction of force acting on the two arms AB and CD.

 Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. 

Therefore the coil and the axle rotate half a turn more in the same direction. 

The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

Significance of split rings :- 

• Act as a commutator .
• Commutator is a devise that reverses the direction of flowe of current 
• Reversal of current results in a continuous rotation of coil.

The commercial motors use (i) an electromagnet in place of permanent magnet: (i) large number of turns of the conducting wire in the current carrying coil; and (iii) a soft iron core on which the coil is wound. 

The soft iron core, on which the coil is wound, plus the coils, is called an armature. This enhances the power of the motor. 

Electromagnetic induction:- Process by which changing magnetic field in a conductor induced current in another conductor.

Application:- electric generator, Wireless charger , elevators, metro trains

1. Faraday 's Experiment 1 

Observations:-

• Relative motion between magnet and coil induced electric current in the coil 

2. Faraday 's Experiment 2

Observations:- 

• Relative motion between coil induce electric current.

3. Faraday 's Experiment 3

Observations:-

• Relative motion is not an absolute requirement for inducing current.

Faraday 's  Law of induction:-

First law:- 

• An EMF is induced in circuit whenever the amount of magnetic flux (no. Of magnetic field lines per unit area) linked with a circuit changes.

Second law:- 

• Magnitude of induced EMF in a circuit is equal to time rate of change of magnetic flux through the circuit.

Methods of producing induced EMF:- 

• Varying magnetic field (B)
• Varying area(A)
• Varying relative orientation of coil and magnetic field,

Direction of induced current:-

Fleming 's right hand rule:- 

• Stretch the thumb forefinger and middle finger of right hand so that they are perpendicular to each other . If forefinger indicates the Direction of magnetic field , thumb shows the direction of motion of current then the middle finger will show the Direction of induced current. This is Fleming right hand rule.

* Electric Generator:- 

• Device that convert mechanical energy into electric energy

-Principle Based on Electromagnetic Indrection

•  It says that current is  induced in coil /loop through change in its orientation or a change in its effective area.

Types of Electric Generator :-

• AC Generator
• DC Generator

 AC Generator =

• Alternating current is produced which changes its direction after equal intervals  of time

DC Generator:- 

• Direct current is produced which does not changes its direction with time.

- Construction AC Generator:-

• Rectangular coll induced copper
• Magnetic poles
• split rings.
• Axle
• Brushes
• • Galvanometer

* working of Electric generator :- 

• When the axle attached to two rings is  rolated such that arm AB moves up & CD moves down in the magnetic Field produced by permanent magnet, It rolates the coil clockwise
• By applying Fleming's & right hand, the induced current flows in  direction ABCD
•  Thus in external circult, current flows from B₂ to B₁
• After half a rotation.arm CD starts moving up & AB moving down. 
• As a result induced current in both arms changes, giving rise to net induced current in direction DCBA
• Now in External circuit , current flows from B1 to B2.
• Thus after half a rotation, polarity of current in respective arms changes.
• such a current which changes its direction. after equal intervals of time is called alternating current
• This device is called AC Generator

Note :-If there are larger numbers of turns in  the coil, the current generated in each turn adds up to give large current through coil.

DC Generator - Working

• split ring commutator is used to ensure unidirections flow of current.
•  with this, one brush is at all times contact with arm moving down.
•  This generator is thus called a DC generator

Difference the AC & DC

• DC flows in one direction always

 •Ac flows by reverses its directions periodically

• AC Changes direction after every 1/100 sec. Frequency of AC is 50 Hz

• AC Can transmitted over  long distance without much loss of energy.

Domestic electric current:- 

• In our homes, we receive supply of electric power through a main supply (also called mains), either supported through overhead electric poles or by underground cables.
• For safe conduction , we use 3 coated wire,
•  One with red insulation cover, is called live wire (or positive).
•  Second wire, with black insulation, is called neutral wire (or negative). 
• And third with green coat called earth wire.
• In our country, the potential difference between the two is 220 V.

At the meter-board in the house, these wires pass into an electricity meter through a main fuse. 

Through the main switch they are connected to the live wires in the house. 

These wires supply electricity to separate circuits within the house. 

Often, two separate circuits are used, one of 15 A current rating for appliances with higher power ratings such as geysers, air coolers, etc. 

The other circuit is of 5 A current rating for bulbs, fans, etc. 

Functions of green wire:-

• The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. 
• This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan. refrigerator, etc.
•  The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. 
• Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.

Fuse:-

• Electric fuse is an important component of all domestic circuits. 
• It is a safety device which prevents the damage to appliances and the circuit due to overloading.. 
• Overloading can occur when the live wire and the neutral wire come into direct contact. (This occurs when the insulation of wires is damaged or there is a fault in the appliance.)
•  In such a situation, the current in the circuit abruptly increases. 
• This is called short-circuiting.

 The use of an electric fuse prevents the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current. 

The Joule heating that takes place in the fuse melts it to break the electric circuit.

 Overloading can also occur due to an accidental hike in the supply voltage.

 Sometimes overloading is caused by connecting too many appliances to a single socket.

Thank you...

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