Saturday, June 6, 2015

2. Solid State - JEE Main - Core Revision Points

Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.


JEE Syllabus (2015)  on Solid State Topic


Solid State: Classification of solids: molecular, ionic, covalent and metallic solids, amorphous and crystalline solids (elementary idea); Unit cell and lattices, packing in solids (fcc, bcc and hcp lattices), voids,   Bragg’s Law and its applications; calculations involving unit cell parameters, imperfection in solids; Electrical, magnetic and dielectric properties.


Jauhar, CBSE XII class

Sections in the Chapter


2.1 Space Lattices and Unit Cell
2.2 Close Packing in Crystalline Solids
2.3 Interstitial Sites or Interstitial Voids
2.4 Types of Cubic Crystals and Number of Atoms per Unit Cell
2.5 Experimental Methods of Determining Crystal Structure: X Rays Diffraction
2.6 Coordination Number and Radius Ratio
2.7 Ionic Radii
2.8 Calculation of Density of a Crystal from its Structure
2.9 Structures of Ionic Compounds
2.10 Imperfections in solids
2.11 Properties of solids
2.12 Amorphous solids


Solid State - Revision Points



The main content covered in the chapter is about the formation of crystals in solids. Last section 2.12 is about amorphous solids which are not crystalline solids.


Solids can be broadly classified into two categories: crystalline and amorphous.


Crystalline solids


The outstanding features are its flat faces and share edges which in a well developed form are usually arranged symmetrically.  Therefore, there is a high degree of internal order throughout the crystal. There is a definite pattern constantly repeating in space that forms the crystal. This order in the crystal is known as long-range order.

Amorphous solids


Amorphous solids are not crystals and they do not have long range order but have short-range order. An ordered arrangement exists around some atoms, molecules or ions only up to short distances. The same order will not be found around other atoms or molecules in the solid at another place. In many was amorphous solids are more closely related to liquids and are therefore regarded as supercooled liquids with high viscosity.  Some crystalline materials can be converted into amorphous or glassy form by rapidly cooling the melt. Freezing the vapours also gives rise to amorphous solids.

Bonds Present in  Solids



Molecular bonds:  In these solids, the constituent particles are molecules. The molecules are held together by weak Van der Waals forces. Examples are iodine, ice and solid carbon dioxide.

Ionic bonds:  Ionic solids have positively and negatively charged ions which are arranged in crystal form and held together by strong electrostatic forces. Examples are salts like NaCl, NaNO3, LiF and Na2SO4 etc.

Covalent bonds:  In these solids, the constituent particles are atoms and they are held together by covalent bonds. Examples are diamond, silicon carbide, and silica.


Metallic bonds: In solids with metallic bonds, positive kernels are immersed in a sea of mobile electrons. The forces between the constituents, positive kernels and electrons form the metallic bonds. These bonds are present in metals like copper, nickel etc.

2.1 Space Lattice and Unit Cell


The crystalline solids have their constituent particles - molecules, ions or atoms at specific locations in a three dimensional space, the basic shape of which repeats many times to form the crystalline solid.  The arrangement of this infinite set of points at which the constituent particles of the solid exist is called space lattice.

Space Lattice


A space lattice is a regular arrangement of the  constituent particles of a crystalline solid in three dimensional space. These points are called lattice points.

Unit Cell


A unit cell is the smallest repeating unit in space lattice.



Parameters to describe a unit cell


Six parameters are required.  The unit cell is assumed to be formed of straightline in three axes.

These the three basic vectors along three crystallographic axes are termed (a,b, and c). Three angles are there between the crystallographic axes (α,β,γ). The angle α is between the edges b and c, The angle β is between edges c and a. The angle γ is between the edges b and a.


Seven Crystal Systems


Crystals can be classified into seven categories


Triclinic -  a is not equal to b  is not equal to - (α,β,γ) are different and not equal to 90 degrees

Monoclinic

Orthoclinic

Trigonal or Rhombohedral

Cubic

Tetragonal

Hexagonal


2.2   Close Packing in Crystalline Solids

In the formation of crystals, closed packing of the constituent particles takes place.



Square Pattern

To understand arrangement of the particles in a solid one can visualise four particles arranged as a square. In this one particle assumed as a sphere is above another particles and four such sphere form a square and the pattern is repeated. But this pattern is not the usual pattern because only 52.4% of the available space becomes occupied in this square pattern of packing.

Hexagonal Pattern

In hexagonal close packing of particles (assumed as spheres), the spheres in the second row are placed in the depressions between the spheres in the first row. (In earlier square pattern, a sphere is placed on another sphere. But now a sphere is placed in the depression between two spheres in  the row below. In this packing, 60.4% of space gets occupied. Hence this hexagonal close packing gives more close packing.

Co-ordination Number

The number of spheres which are touching a given sphere in packing arrangement is called co-ordination number. Thus in two dimensional representation coordination number is 4 in square arrangement and six in hexagonal arrangement.




2.3 Interstitial Sites or Interstitial Voids

In the packed structure of the crystalline solid, there are hollow spaces between particles. These holes are voids are called interstitial sites or interstitial voids. Two important interstitial sites are 1. Tetrahedral interstitial site.  (2) Octahedral interstitial site.


2.4 Types of Cubic Crystals and Number of Atoms per Unit Cell

There are three common types of cubic crystals.

1. Simple cubic
2. Body centred cubic
3. Face centred cubic or cubic close packing

2.5 Experimental Methods of Determining Crystal Structure: X Rays Diffraction


The structure of solid is studied by X-ray diffraction methods.

Bragg Equation:

n lamba = 2d sin theta

where d = distance between the planes of the constituent particles of the  crystal.
lamba = wave length of the x-ray used.
n =  1,2,3 etc.  standing for the serial order of the diffracted beam.


2.6 Coordination Number and Radius Ratio
2.7 Ionic Radii
2.8 Calculation of Density of a Crystal from its Structure
2.9 Structures of Ionic Compounds
2.10 Imperfections in solids
2.11 Properties of solids
2.12 Amorphous solids


close packed structure of solids (cubic), packing in fcc, bcc and hcp lattices;

packing of crystals;
Body centred cubic(bcc),
Hexagonal closed packed (hcp) and

cubical close packed (ccp)

Point defects: Schottsky defects, Frenkel defects





See an Oxford Video on Crystal Structure
09. Geometry of Solids I: Crystal Structure in Real Space
http://podcasts.ox.ac.uk/09-geometry-solids-i-crystal-structure-real-space

Good Websites for Solid State Topic

Updated 6 June 2015
Originally published  22 May 2015

Good Websites for topic Solid State - Chapter Two in Jauhar




Oxford Video on Crystal Structure
09. Geometry of Solids I: Crystal Structure in Real Space
http://podcasts.ox.ac.uk/09-geometry-solids-i-crystal-structure-real-space



https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidstate.htm


http://www.seas.upenn.edu/~chem101/sschem/solidstatechem.html




Future use of the material in this topic

The material is solid state is further useful in the topic of Solid State Electronics - Semiconductors




The website below was not found when checked on 6 June 2015

http://www.chem.ox.ac.uk/icl/heyes/structure_of_solids/Strucsol.html




Contents

Lecture 1. Fundamental Aspects of Solids & Sphere Packing.


1. Why Study Solids?

2. Some crystallographic ideas

lattice (lattice types)
motif (basis)
crystal structure
unit cell (counting atoms in unit cells)
fractional coordinates
coordination number


3. Representations of structures

Perspective (Clinographic)
Projection (Plan) diagrams

4. Close-Packing of spheres

hexagonal close packing (hcp)
cubic close packing (ccp)

5. Structures of metallic elements

6. Interstitial sites in close-packed arrangements


Updated 6 June 2015
Originally posted  1 June 2007

JEE - Study Guide - 2. Solid State



JEE Syllabus (2015)

Solid State: Classification of solids: molecular, ionic, covalent and metallic solids, amorphous and crystalline solids (elementary idea); Bragg’s Law and its applications; Unit cell and lattices, packing in solids (fcc, bcc and hcp lattices), voids, calculations involving unit cell parameters, imperfection in solids; Electrical, magnetic and dielectric properties.





Jauhar, CBSE XII class

Sections in the Chapter

2.1 Space Lattices and Unit Cell
2.2 Close Packing in Crystalline Solids
2.3 Interstitial Sites or Interstitial Voids
2.4 Types of Cubic Crystals and Number of Atoms per Unit Cell
2.5 Experimental Methods of Determining Crystal Structure: X Rays Diffraction
2.6 Coordination Number and Radius Ratio
2.7 Ionic Radii
2.8 Calculation of Density of a Crystal from its Structure
2.9 Strctures of Ionic Compounds
2.10 Imperfections in solids
2.11 Properties of solids
2.12 Amorphous solids



Additional numerical problems for practice 12
Conceptual Questions with Answers: 13
Key facts to remember
Revision Exercises: Very Short Answer questions 40
Short Answer Questions : 50
Long Answer Questions : 6

Competition File
Some useful facts
numerical problems 9

Objective Questions: Multiple choice 25
Fill in the blanks: 10
Matching type question 1

Study Plan

Day 1

2.1 Space Lattices and Unit Cell
2.2 Close Packing in Crystalline Solids
2.3 Interstitial Sites or Interstitial Voids

Day 2
2.4 Types of Cubic Crystals and Number of Atoms per Unit Cell
Practice problems 2.1 to 2.3

Day 3

2.5 Experimental Methods of Determining Crystal Structure: X Rays Diffraction
P.P. 2.4,2.5
2.6 Coordination Number and Radius Ratio
P.P. 2.14 to 2.17
Day 4

2.7 Ionic Radii
2.8 Calculation of Density of a Crystal from its Structure

Day 5
P.P. 2.8 to 2.19

Day 6

2.9 Strctures of Ionic Compounds
P.P 2.20 to 2.25

Day 7
2.10 Imperfections in solids
2.11 Properties of solids
2.12 Amorphous solids

Day 8


Concept revision
Additional numerical problems for practice 12

Day 9


Conceptual Questions with Answers: 13
Key facts to remember

Day 10

Revision Exercises: Very Short Answer questions 40

Revision period

Day 11
Revision Exercises:Short Answer Questions : 1 to 15

Day 12
Revision Exercises:Short Answer Questions : 16 to 30

Day 13
Revision Exercises:Short Answer Questions : 31 to 50

Day 14

Competition File
Some useful facts
numerical problems 9

Day 15

Objective Questions: Multiple choice 25

Day 16
Fill in the blanks: 10
Matching type question 1

Day 17 to 20

Concept revision and test paper questions/problems




Updated   6 June 2015
Originally published 11 March 2009

Sunday, May 24, 2015

Ch.2 States of Matter - JEE Main Core Points for Revision

Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.

Matter exists in three physical states, solid, liquid, and gaseous.

Solid State: A substance in solid state has a definite size (volume) and a definite shape. As we know shape can be changed by applying force. It can be broken into pieces by hammering etc. The solids are hard and rigid. Some common solids in article share we see are stainless plates and glasses. We also use things like combs, mirrors, scooters and cars. Some of the elements that we see in solid shape are iron, aluminium, silver,and gold etc.

Liquid State: A liquid possesses definite volume but not a definite shape.

Gaseous State: A gas of a given mass, neither possesses a definite volume nor definite shape.

Contents of the Chapter

2.1 Intermolecular Forces Versus Thermal Energy of Three States of Matter
2.2 Measurable Properties of Gases
2.3 Gas Laws
2.4 Some Problems Involing Chemical Equations

2.6 Kinetic Molecular Theory of Gases
2.7 Maxwell-Boltzmann Distribution of molecular Speeds
2.8 Deviations from Ideal Gas Behavior - Real Gases
2.9 Liquification of Gases and Their  Critical Phenomena
2.10 Kinetic Molecular Model of Liquids
2.11 Properties of Liquids
2.12 Charateristics of Solids
2.13 Classification of Solids
2.14 Size andShare of Crystals
2.15 Types of Solids on the basis of Binding Forces
2.16 Intermolecular Forces


Core Revision Points of the Chapter States of Matter

2.1 Intermolecular Forces Versus Thermal Energy of Three States of Matter



Particle concept of matter: According to this concept, all matter consists of tiny particles (atoms or molecules) which are constantly moving in all directions. These particles exert attractive forces upon one another called inter particle (intermolecular) forces.

2.2 Measurable Properties of Gases


1. Measurement of Mass
2. Measurement Volume
3. Measurement of Pressure
4. Measurement of Temperature

2.3 Gas Laws


1. Boyle's Law
2. Charles' Law
3. Avogadro Law
4. The Combined Gas Lawor Ideal Gas Equation
5. Dalton's Law of Partial Pressures
6. Graham's Law of Diffusion or Effusion



1. Boyle's Law
2. Charles' Law
3. Avogadro Law
4. The Combined Gas Law or Ideal Gas Equation

2.4 Some Problems Involing Chemical Equations

2.5 Dalton's Law of Partial Pressures






6. Graham's Law of Diffusion or Effusion


When a cylinder of colourless hydrogen gas inverted over a cylinder of brown bromine vapour, after some time, we can see that both the cylinders become yellowish brown. This means hydrogen has travelled to the lower cylinder and bromine vapour moved to the upper cylinder.

Gases have the tendency to intermix and to form a homogeneous mixture. This property is known as diffusion.

Diffusion is defined as the process of intermixing of two or more gases, irrespective of density relationship adn without the help of external agency.


Graham's Law of Diffusion: The rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass.


Effusion: Effusion is a special case of diffusion wherein a gas escapes through a small aperture from the vessel in which it is contained.

The rate of escape is inversely proportional to the square root of its density or molar mass.

2.6 Kinetic Molecular Theory of Gases


The important postulates of the Kinetic Molecular Theory

1. Gases consist of large number of minute particles called molecules.
2. The molecules are separated by large distances. The empty space in gas is so large that the actual volume occupied by the molecules is negligible when compared to the total volume of the gas.
3. Molecules of the gas are in state of random motion in all directions. In this motion they keep on colliding with each other and also the walls of the container.
4. Collisions between molecules as well as between molecules and walls of the container are elastic. It means there is no loss of energy in the system due to collisions. There may be redistribution of energy among molecules.
5. There are no forces of attraction or repulsion between molecules.
6. The pressure exerted by a gas on the walls of a container is due to the collision of the molecules.
7. The average kinetic energy of translational motion of gas molecules is directly proportional to the absolute temperature of the gas.

2.7 Maxwell-Boltzmann Distribution of molecular Speeds


Average, root mean square and most probable velocities and their relation with temperature;


Molecular Speeds

From the expression for kinetic temperature

Substitution gives the root mean square (rms) molecular velocity:

From the Maxwell speed distribution this speed as well as the average and most probable speeds can be calculated.

http://hyperphysics.phy-astr.gsu.edu/Hbase/kinetic/kintem.html

2.8 Deviations from Ideal Gas Behavior - Real Gases


Van der Wals' equation for real gases

2.9 Liquification of Gases and Their  Critical Phenomena


Critical temperature is the temperature above which a gas cannot be liquefied however high the pressure may be.

2.10 Kinetic Molecular Model of Liquids

 1. Liquids are composed of molecules.
2. There are appreciable intermolecular forces between molecules that hold them together in the liquid.
3. Still, the intermolecular forces are weak, hence molecules of liquids are in constant random motion.
4. The average kinetic energy of molecules in a given sample is proportional to the absolute temperature.

2.11 Properties of Liquids



1. Volume
2. Density
3.Compressibility
4. Diffusion
5. Evaporation
6. Enthalpy of vaporisastion

7.Vapour Pressure

When a liquid is placed in a vessel and is covered with jar, from the liquid evaporation takes place and the vapour of the liquid or molecules of the liquid in gap form fill the available space. As the evaporation takes place over a period of time, the number of gaseous molecules goes up. As evaporation is taking place some molecules in the gaseous phase collide with the surface of the liquid and become liquid molecules. Thus both evaporation and condensation take place simultaneously. But initially there is more evaporation and less condensation. At the some stage, rate of evaporation equals rate of condensation and equilibrium is established between gas and liquid phases. The pressure exerted by the vapours at the equilibrium stage is called vapour pressure.

Definition
The pressure exerted by the vapours above the liquid surface (in a closed vessel) in equilibrium with the liquid at a given temperature is called vapour pressure.

Vapour pressure changes from liquid to liquid. It depends on intermolecular forces. if the forces in a liquid are weak, there is more gas formation and hence more vapour pressure.

A higher temperature there is more gas formation and hence for the same liquid vapour pressures increase with temperature.

8. Boiling
9. Surface tension
10. Viscosity

2.12 Charateristics of Solids


1. Solids are rigid and have definite shape


2.13 Classification of Solids


1. Crystalline Solids  2. Amorphous Solids

2.14 Size and Share of Crystals


Law of constancy of interfacial angles of a crystal,

2.15 Types of Solids on the basis of Binding Forces


1. Molecular crystals
2. Iconic crystals
3. Covalent crystals
4. Metallic crystals

2.16 Intermolecular Forces


In addition to normal covalent bond, ionic bond, and metallic bond, there are weak attractive intermolecular forces which occur in all kinds of molecular solids. These are present in case of non-polar molecules such as H2, O2, CO2, CH4 etc. also.

These are classified as:
i) Dipole-dipole forces
ii) Dipole induced dipole forces
iii) Instantaneous dipole-instantaneous induced dipole forces (called London forces)
iv) Hydrogen bonding

JEE Main - Chapters - Modern Chemistry for Class XI by Dr. S.P. Jauhar

1. Some basic concepts of chemistry

Study Guide - 15 Days

Core Revision Points

Notes

2. States of Matter

Study Guide - 13 Days

Core Revision Points

Notes

3. Atomic Structure

Study Guide - 12 Days

Core Revision Points

Notes

4. Classification of Elements and Periodicity in Properties

Study Guide

Core Revision Points

5. First Law of Thermodynamics and Chemical Energetics

Study Guide

Core Revision Points

Notes

6. Chemical Bonding and Molecular Structure

Study Guide

Core Revision Points

Notes

7. Equilibrium I – Equilibrium Process and Phase Equilibria

Study Guide

Core Revision Points

Notes

8. Equilibrium II – Ionic Equilibrium in Solutions

Study Guide

Core Revision Points

Notes

9. Redox Reactions

Study Guide

Core Revision Points

Notes

10. Principles and Processes of Extraction of Elements

Study Guide

Core Revision Points

Notes

11. Hydrogen

Study Guide

Core Revision Points

12. s-Block Elements

Study Guide

Core Revision Points

Notes

13. Some p-Block Elements

Study Guide

Core Revision Points

Notes

14. Organic Chemistry: Some Basic Principles

Study Guide

Core Revision Points

15. Hydrocarbons

Study Guide

Core Revision Points

Alkanes - Revision Notes

Alkenes

Alkynes

Aromatics - Benzene

16. Purification and Characterisation of Organic Compounds

Study Guide

Core Revision Points

17. Organic Compounds with Functional Groups Containing Halogens

Study Guide

Core Revision Points

Alkyl halides

18. Environmental Pollution

Study Guide

Core Revision Points



Updated 24 May 2015
First posted 20 Dec 2014

Saturday, May 23, 2015

Ch.1 Atomic Structure and Chemical Bonding - JEE Main Core Revision Points

Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.

Sections in the Chapter

1.1 Dual Nature of Radiation
1.2 Dual Nature of Matter - de-Broglie Equation
1.3 Heisengberg's Uncertainty Principle
1.4 Wave Mechanical Model of Atom and Concept of Atomic Orbital
1.5 Quantum Numbers

1.6 Pauli's Exclusion Principles
1.7 Orbital Wave Functions and Shapes of Orbitals
1.8 Electronic Configurations of Atoms
1.9 Chemical Bonding
1.10 Review of Valency Bond Theory

1.11 Molecular Orbital Theory
1.12 Linear Combination of Atomic Orbitals (LCAO) Method
1.13 Relative Energies of Bonding and Antibonding Molecular Orbitals
1.14 Combination of 2s and 2p Atomic Orbitals to form Molecular Orbitals
1.15 Conditions for the Combination of Atomic Orbitals

1.16 Energy Level diagram for Molecular Orbitals
1.17 Rules for Filling Molecualr Orbitals
1.18 Electronic Configurations and Molecular Behavior
1.19 Bonding in Some Diatomic Molecules
1.20 Metallic Bond

1.21 Hybridisation
1.22 Intermolecular Forces
1.23 Hydrogen Bonding



Revision Points for Various Sections in the Chapter


1.1 Dual Nature of Radiation

Einstein in 1905 suggested that light has a dual character - Particle nature as well as wave.

Wave like character of light was proposed by Huygens.  In 1856, James Maxwell proposed that light and other forms of radiation propagate though space in the form of waves and these waves have electric and magnetic fields associated with it. Therefore, the light which is travelling through radiation is said  to be composed of electromagnetic waves.

Planck's Quantum Theory of Radiation



1.2 Dual Nature of Matter - de-Broglie Equation

In 1924, Louis de Broglie suggested that similar to light, all microscopic material particles in motion have dual character.

1.3 Heisengberg's Uncertainty Principle


Uncertainty principle

In 1927, Heisenberg put forward a principle known as Heisenberg’s uncertainty principle.

According it, “it is not possible to measure simultaneously both the position and momentum (or velocity) of a microscopic particle, with absolute accuracy.”

Mathematically, this principle is expressed as:

∆x * ∆p = h/4 π

Where
∆x = uncertainty in position

∆p = uncertainty in momentum

The constancy of the product of uncertainties means that, if the position of the particle is known with more accuracy, there will be large uncertainty in momentum and vice versa.

This uncertainty arises, as all observations are made by impact of light, the microscopic objects suffer a change in position or velocity as a result of impact of light. So there is a disturbance in them due to the measurement.

The principle does not affect the measurement of large objects as in these cases impact of light does not created any appreciable change in their position or velocity.

1.4 Wave Mechanical Model of Atom and Concept of Atomic Orbital

Quantum mechanics or wave mechanics is a theoretical science which deals with the study of the motion of the micrscopic objects (like electron) which have both observable wave like and particle like properties.

Quantum mechanics was developed indepdendently in 1926 by Werner Heisenberg and Erwin Schrodinger. In 1927, Schrodinger wave equation was published.

1.5 Quantum Numbers


According to quantum mechanical model or wave mechanical model of atom, orbitals represent regions in space around the nucleus where the probability of finding electrons is maximum. A large number of orbitals are possible in an atom.

To describe each electron in an atom in different orbitals, four quantum numbers are used. They are designated as n,l,ml, and ms.



1. Principal quantum number (n) This quantum number determines the main energy shell or level in which the electron is present. It can have whole number values starting from 1 in an atom.

The principle quantum number indicates the average distance of the electron from the nucleus. If n = 1, it is closest to the nucleus and has lowest energy.

Eariest practice was to number shells as K,L,M,N etc.
Shell with principal quantum number n = 1 is called K.
Shell with principal quantum number n = 2 is called etc.

2. Azimuthal quantum number or angular quantum number (l): This number determines the angular momentum of the electron.

It can have positive integer values from zero to (n-1) where n is the principal quantum number. For each value of n, there are n possible values of l.

For n =3, l has three values: l = 0,1,2

The earlier practice is to designate l as subshell and refer it by letters s,p,d,f,….

l=0 = s; l=1=p; l=2=d, l=3=f etc.

The energy of subshell increases with increasing value of l.

3. Magnetic quantum number ( ml): Magnetic field acts on moving electrical charges. ( from chapters on magnetism in physics syllabus). On revolving electrons external magnetic field of the earth acts. Therefore, the electrons in a given subshell orient themselves in certain preferred regions space around the nucleus. These are called orbitals. This quantum number gives the number of orbitals for given angular quantum number l or in a given subshell.

The allowed values of ml are –l through 0 to +l.

There are (2l+1) values of ml for each value of l.

If l = 0, ml has only one value. ml = 0.

If l = 3, ml has 7 values.
ml = -3,-2,-1,0,1,2,3

4. Spin quantum number (ms) : It is observed that the electron in an atom is not only revolving around the nucleus but is also spinning around its own axis. This quantum number describes the spin orientation of the electron.

The electron can spin in two ways – clockwise and anticlockwise.
Values of +1/2 and -1/2 are given to this quantum number. Its value is not dependent on other quantum numbers.

The orientations of spin are also designated by up and down arrows ↑ ↓.

1.6 Pauli's Exclusion Principles


Pauli's exclusion principle: No two electrons can have all four same quantum numbers

1.7 Orbital Wave Functions and Shapes of Orbitals

1. Spherical shape for s.
2. Dumbbell shape for orbitals of p.
3. Four-lobed shape for orbitals of d.
4. Complex shape for all orbitals of higher sublevels

1.8 Electronic Configurations of Atoms

1. Aufbau principles
2. Pauli's exclusion principle: No two electrons can have all four same quantum numbers
3. Hund's rule of maximum multiplicity

1.9 Chemical Bonding

1. Valency bond theory 2. Molecular orbital theory

1.10 Review of Valency Bond Theory

Valency bond theory was proposed by Heitler and London in 1927 and it was further developed by Linus Pauling.

The basic idea of the theory are:

1. A covalent bond is formed by the overlap of half-filled atomic orbitals of the different atoms.
2. The overlapping atomic orbitals must have electrons with opposite spins.


1.11 Molecular Orbital Theory

This theory was proposed by Hund and Mulliken in 1932. The basic idea of the theory is that atomic orbitals of individual atoms combine to form molecular orbitals.

1.12 Linear Combination of Atomic Orbitals (LCAO) Method

According to LCAO method, the orbitals are formed by the linear combination (addition or subtraction) of atomic orbitals of the atoms which form the molecule.


1.13 Relative Energies of Bonding and Antibonding Molecular Orbitals
1.14 Combination of 2s and 2p Atomic Orbitals to form Molecular Orbitals

2s-orbitals combine by addition and subtraction to form bonding and antibonding molecular orbitals.

1.15 Conditions for the Combination of Atomic Orbitals

Main Conditions for the Combination of Atomic Orbitals

1. The combining atomic orbitals should  not differ much in energies.
2. The extent of overlapping between the atomic orbitals of two atoms should be large.
3. The combining atomic orbitals between the atomic orbitals of two atoms should be large.

1.16 Energy Level diagram for Molecular Orbitals

1.17 Rules for Filling Molecualr Orbitals

1. Aufbau principles
2. Pauli's exclusion principle: No two electrons can have all four same quantum numbers
3. Hund's rule of maximum multiplicity

1.18 Electronic Configurations and Molecular Behavior

The important information conveyed by Electron Configuration of a molecule is:

1. Stability of a molecule
2. Bond Order

1.19 Bonding in Some Diatomic Molecules

1. Hydrogen molecule.

1.20 Metallic Bond

More than 80 elements in the periodic table are metals.
The force which holds together atoms of metals is called metallic bond.

1.21 Hybridisation

Hybridizastion is the phenomenon of intermixing of the orbitals of slightly different energies so as to redistribute their energies and to give new set of orbitals of equivalent energy and shape.

1.22 Intermolecular Forces

In addition to normal covalent bond, ionic bond, and metallic bond, there are weak attractive intermolecular forces which occur in all kinds of molecular solids. These are present in case of non-polar molecules such as H2, O2, CO2, CH4 etc. also.

These are classified as:
i) Dipole-dipole forces
ii) Dipole induced dipole forces
iii) Instantaneous dipole-instantaneous induced dipole forces (called London forces)
iv) Hydrogen bonding

1.23 Hydrogen Bonding

When hydrogen atom is bonded to atoms of highly electronegative elements such as fluorine, oxygen, or nitrogen, the hydrogen atom forms a weak bond with the electronegative atom of the other molecule.


First Posted on 23 May 2015

18. Chemistry in Everyday Life - JEE Main - Core Revision Points

Importance of  Core Revision Points: Core Revision Points are important because if you remember them strongly, many more points related to them will come out of your memory and help you to answer question and problems. Read them many times and make sure you remember them very strongly.

Sections in the chapter – Jauhar

18.1 Chemical medicines and health care
18.2 Dyes
18.3 Chemicals in Cosmetics
18.4 Advanced materials
18.5 Chemicals in food
18.6 Detergents
18.7 Insect repellants: pheromones and sex attractants
18.8 Chemistry of rocket propellants



Sections in the chapter – Jauhar

18.1 Chemical medicines and health care
18.2 Dyes
18.3 Chemicals in Cosmetics
18.4 Advanced materials
18.5 Chemicals in food
18.6 Detergents
18.7 Insect repellants: pheromones and sex attractants
18.8 Chemistry of rocket propellants