VSEPR Theory tells us about the basic structure of the molecules based on the force of repulsion between lone pair and bond pair of electrons. It states that any molecule arranged in such a structure minimizes the repulsion between the lone pair and bond pair of the molecule.

Let’s learn more about VSEPR theory in detail, including its postulates, limitations, and examples.

Table of Contents

What is VSEPR Theory?

VSEPR stands for Valence Shell Electron Pair Repulsion. As the name suggests this theory is used to find the shape of the molecule by taking into account the force of the electron pairs and lone pairs of the molecule. According to this theory, any molecule formed by sharing of electron pair between two or more atoms tends to take such shapes that minimize forces between the electron pairs or lone pairs of electrons.

The various geometries of the molecules according to the VSEPR theory are discussed in the table below:

Number of Electron Or Lone Pair	Electron Pair Geometry	No Lone Pair	1 Lone Pair	2 Lone Pairs	3 Lone Pairs	4 Lone Pairs
2	Linear	Linear	–	–	–	–
3	Trigonal Planar	Trigonal Planar	Bent	–	–	–
4	Tetrahedral	Tetrahedral	Trigonal Pyramidal	Bent	–	–
5	Trigonal Bipyramidal	Trigonal Bipyramidal	Sawhorse	T-shaped	Linear	–
6	Octahedral	Octahedral	Square Pyramidal	Square Planar	T-Shaped	Linear

VESPR Theory states that the repulsion between two electrons is because of the Pauli Exclusion Principle.

Postulates of VSEPR Theory

Various postulates of the VSEPR Theory are,

• All the electron pairs in the molecule are arranged in such a way that they minimize the repulsion between the electron pairs of the atom.
• The central atom of the polyatomic atom is the atom to which all the other atoms of the molecule are linked.
• Valance Shell electrons of the molecule are responsible for the shape of the molecule.
• The valence shell of the molecules is arranged in such a way that the distance between them is maximum and the repulsion between them is minimum.
• If the central atom of the molecule is surrounded by bond pairs of electrons, then the asymmetrically shaped molecule is formed.
• If the central atom of the molecule is surrounded by lone pairs and bond pairs of electrons, then the shape of the molecule so formed is distorted.
• In each resonance state of the molecule, their structure is explained using the VSEPR theory.
• The force of repulsion between the lone pairs, lone pair, and bond pair, and bond pairs follows the order.

Lone Pair – Lone Pair > Lone Pair – Bond Pair > Bond Pair – Bond Pair

Predicting Shapes of Molecules

We can easily predict the shape of the molecules using the VESPR theory using the following rules :

• The least electronegative element of the molecule must be chosen as the central element. This atom can easily share its electron with other atoms of the molecule.
• The lone pairs of the central atom are counted by taking the central atom’s outermost shell into account.
• The electrons shared by other atoms with the central atom are accounted as the bond pair of electrons.
• The lone pair and the pair are sums to find the VESP number of the molecule which is used to explain the shape of the molecule.

VSEP Number

VSEP number of a molecule is the number that describes the shape of the molecule. We easily find this number by taking the sum of the Lone Pairs and Bond Pairs of the molecule. Various Shapes of molecules according to the VSEP number is tabulated below:

VSEP Number	Shape of Molecule
2	Linear Structure
3	Trigonal Planar Structure
4	Tetrahedral Structure
5	Trigonal Bipyramidal Structure
6	Octahedral Structure
7	Pentagonal Bipyramidal Structure

The various shape of the molecules are discussed in the article below,

Linear Shape of Molecule

The molecule in a linear shape is arranged in such a way that it has two valance shells and the bond pair in this arrangement are arranged in such a manner that their repulsion is minimum, this is achieved by taking the bond pair in opposite directions.

BeF₂ is an example of a Linear Shape Molecule.

Trigonal Planar Shape of Molecule

There are three molecules attached to the central atom in the Trigonal Planer molecule. The molecules in the trigonal planar structure are arranged in the form of an equilateral triangle which helps them to reduce the repulsion between the electron pairs of the atoms.

BF₃ is an example of a Trigonal Planar Shape Molecule.

Tetrahedral Shape of Molecule

There are four molecules attached to the central atom in the Tetrahedral molecule. The molecules in the tetrahedral structure are arranged in the form of a tetrahedron, which helps them to reduce the repulsion between the electron pairs of the atoms.

CH₄ is an example of a Tetrahedral Shape Molecule.

Trigonal Bipyramid Shape of Molecule

There are five molecules attached to the central atom in the Trigonal Bipyramid molecule. The molecules in the trigonal bipyramid structure are arranged in the form of a triangular pyramid, which helps them to reduce the repulsion between the electron pairs of the atoms.

PF₅ is an example of a Trigonal Bipyramid Shape Molecule.

Octahedral Shape of Molecule

In Octahedral shape, the central atom attaches 6 different atoms i.e. in total there are 6 bond pairs. These 6 bond pairs and the central atom arrange Octahedral to minimize electron repulsion.

An example of an Octahedral Shape is SF_6.

Pentagonal Bipyramidal Shape of Molecule

In Pentagonal Bipyramidal Shape, the central atom is attached to seven atoms at the corner to minimize the repulsion between the electron pairs. 

An example of a Pentagonal Bipyramidal Shape is IF_7.

VSEPR Shapes of Molecules

We know that VSPER theory minimizes the force between the bond pair and lone pair electrons of atoms and the structure so formed also follows this rule. So using this theory we can easily predict the shape of the molecule if all the bond pairs and the lone pairs of the molecule are known to us.

The force of repulsion between Lone Pair- Lone Pair, Lone Pair- Bond Pair, Bond Pair- Bond Pair (BP – BP) is in the order mentioned below:

Lone Pair- Lone Pair (LP – LP) > Lone Pair- Bond Pair (LP – BP) > Bond Pair- Bond Pair (BP – BP)

Now we can predict the shape of the molecule by first finding the total electron pairs around the central atom using the formula,

Total Electron Pairs =  ½ (Number of Valence Electrons of Central Atom + Number of atoms attached to Central Atom by single bonds)

For Negative and Positive ions electron pairs are calculated as,

Negative Ions: In negative ions, we add the number of electrons equal to the units of negative charge on the ion to the valance electrons of the central atom.

Positive Ions: In positive ions, we subtract the number of electrons equal to the units of positive charge on the ion from the valance electrons of the central atom.

• If we have only two atoms then the shape of the molecule so formed is linear.
• If the central atom is only surrounded by the bond pair of similar atom then the structure of the atom is symmetrical and have regular geometry.
• If the central atom is only surrounded by the bond pairs and lone pair of electrons then the structure of the atom is unsymmetrical because of the lone pair-lone pair and bond pair-lone pair repulsions, and thus the structure so formed have a distorted geometry.

Limitations of VSEPR Theory

The limitations of VESPR Theory are :

• It fails to account for the different structures of isoelectronic species (i.e. elements having the same number of electrons). Why do these species having the same number of electrons, differ in their shapes?
• It is unable to explain the formation of metal complexes.
• The bent structure of halides is also not explained using the VESPR theory.

FAQs on VSEPR Theory

What is VSEPR Theory Full Form?

The full form of VSEPR Theory is Valence Shell Electron Pair Repulsion Theory.

What is VSEPR Theory?

VSEPR Theory is the fundamental theory of Chemistry that is used to define the structure of various molecules. this theory states that molcecule so formed are arranged in such a structure that they minimise the repulsion between the atoms.

What is VSEPR Theory used to predict?

The VSEPR Theory is used to predict the geometry of molecules based on the repulsion between electron pairs around a central atom.

Who was VSEPR Theory Proposed by?

The VSEPR Theory was proposed by Ronald J. Gillespie and Ronald S. Nyholm.

What is VSEP Number?

VSEP number is a number that is used to define the structure of any molecule using VSEPR theory. It is calculated by taking into account the valance electrons, bond pairs, charge on the species of the molecule.

What are Advantages of VSEPR Theory?

VSEPR theory provides the basic of the formation of the structure of any molecule. This theory helps us to define the shape of various molecules which in turns help us to define its various physcial and chemical properties.

What are Limitations of VSEPR Theory?

There are a few limitations of VSEPR Theory that includes,

• We can not explain the structure of isoelectric species using the VSPER Theory.
• Metal complexes are not explained using the VSPER theory, etc.

What is Shape of NH₃ using VSEPR Theory?

In NH₃ the central atom will be N, which has 5 valence electrons. Out of five, three electrons will make bonds with 3 H atoms and one pair of electrons will be lone pair. Hence there is a total of 3 Bond Pairs and 1 Lone Pair i.e. a total of 4 electron pairs thus the shape of NH₃ will be a tetrahedral structure.

What is the VSEPR Shape of CO₂?

The VSEPR shape of CO₂ (Carbon Dioxide) is linear.

What is VSEPR Shape of H₂O?

The VSEPR shape of H₂O (Water) is bent (or V-shaped).

Neeraj Anand, Param Anand

Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations. In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS". He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.

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CBSE Class 11 Chemistry Syllabus

CBSE Class 11 Chemistry Syllabus is a vast which needs a clear understanding of the concepts and topics. Knowing CBSE Class 11 Chemistry syllabus helps students to understand the course structure of Chemistry.

Unit-wise CBSE Class 11 Syllabus for Chemistry

Below is a list of detailed information on each unit for Class 11 Students.

UNIT I – Some Basic Concepts of Chemistry

General Introduction: Importance and scope of Chemistry.

Nature of matter, laws of chemical combination, Dalton’s atomic theory: concept of elements,
atoms and molecules.

Atomic and molecular masses, mole concept and molar mass, percentage composition, empirical and molecular formula, chemical reactions, stoichiometry and calculations based on stoichiometry.

UNIT II – Structure of Atom

Discovery of Electron, Proton and Neutron, atomic number, isotopes and isobars. Thomson’s model and its limitations. Rutherford’s model and its limitations, Bohr’s model and its limitations, concept of shells and subshells, dual nature of matter and light, de Broglie’s relationship, Heisenberg uncertainty principle, concept of orbitals, quantum numbers, shapes of s, p and d orbitals, rules for filling electrons in orbitals – Aufbau principle, Pauli’s exclusion principle and Hund’s rule, electronic configuration of atoms, stability of half-filled and completely filled orbitals.

UNIT III – Classification of Elements and Periodicity in Properties

Significance of classification, brief history of the development of periodic table, modern periodic law and the present form of periodic table, periodic trends in properties of elements -atomic radii, ionic radii, inert gas radii, Ionization enthalpy, electron gain enthalpy, electronegativity, valency. Nomenclature of elements with atomic number greater than 100.

UNIT IV – Chemical Bonding and Molecular Structure

Valence electrons, ionic bond, covalent bond, bond parameters, Lewis structure, polar character of covalent bond, covalent character of ionic bond, valence bond theory, resonance, geometry of covalent molecules, VSEPR theory, concept of hybridization, involving s, p and d orbitals and shapes of some simple molecules, molecular orbital theory of homonuclear diatomic molecules(qualitative idea only), Hydrogen bond.

UNIT V – Chemical Thermodynamics

Concepts of System and types of systems, surroundings, work, heat, energy, extensive and intensive properties, state functions. First law of thermodynamics – internal energy and enthalpy, measurement of U and H, Hess’s law of constant heat summation, enthalpy of bond dissociation, combustion, formation, atomization, sublimation, phase transition, ionization, solution and dilution. Second law of Thermodynamics (brief introduction)
Introduction of entropy as a state function, Gibb’s energy change for spontaneous and nonspontaneous processes.
Third law of thermodynamics (brief introduction).

UNIT VI – Equilibrium

Equilibrium in physical and chemical processes, dynamic nature of equilibrium, law of mass action, equilibrium constant, factors affecting equilibrium – Le Chatelier’s principle, ionic equilibrium- ionization of acids and bases, strong and weak electrolytes, degree of ionization,
ionization of poly basic acids, acid strength, concept of pH, hydrolysis of salts (elementary idea), buffer solution, Henderson Equation, solubility product, common ion effect (with illustrative examples).

UNIT VII – Redox Reactions

Concept of oxidation and reduction, redox reactions, oxidation number, balancing redox reactions, in terms of loss and gain of electrons and change in oxidation number, applications of redox reactions.

UNIT VIII – Organic Chemistry: Some basic Principles and Techniques

General introduction, classification and IUPAC nomenclature of organic compounds. Electronic displacements in a covalent bond: inductive effect, electromeric effect, resonance and hyper conjugation. Homolytic and heterolytic fission of a covalent bond: free radicals, carbocations, carbanions, electrophiles and nucleophiles, types of organic reactions.

UNIT IX – Hydrocarbons

Classification of Hydrocarbons
Aliphatic Hydrocarbons:
Alkanes – Nomenclature, isomerism, conformation (ethane only), physical properties, chemical reactions.
Alkenes – Nomenclature, structure of double bond (ethene), geometrical isomerism, physical properties, methods of preparation, chemical reactions: addition of hydrogen, halogen, water, hydrogen halides (Markovnikov’s addition and peroxide effect), ozonolysis, oxidation, mechanism of electrophilic addition.
Alkynes – Nomenclature, structure of triple bond (ethyne), physical properties, methods of preparation, chemical reactions: acidic character of alkynes, addition reaction of – hydrogen, halogens, hydrogen halides and water.

Aromatic Hydrocarbons:

Introduction, IUPAC nomenclature, benzene: resonance, aromaticity, chemical properties: mechanism of electrophilic substitution. Nitration, sulphonation, halogenation, Friedel Craft’s alkylation and acylation, directive influence of functional group in monosubstituted benzene. Carcinogenicity and toxicity.

To know the CBSE Syllabus for all the classes from 1 to 12, visit the Syllabus page of CBSE. Meanwhile, to get the Practical Syllabus of Class 11 Chemistry, read on to find out more about the syllabus and related information in this page.

CBSE Class 11 Chemistry Practical Syllabus with Marking Scheme

In Chemistry subject, practical also plays a vital role in improving their academic scores in the subject. The overall weightage of Chemistry practical mentioned in the CBSE Class 11 Chemistry syllabus is 30 marks. So, students must try their best to score well in practicals along with theory. It will help in increasing their overall academic score.

CBSE Class 11 Chemistry Practical Syllabus

The experiments will be conducted under the supervision of subject teacher. CBSE Chemistry Practicals is for 30 marks. This contribute to the overall practical marks for the subject.

The table below consists of evaluation scheme of practical exams.

CBSE Syllabus for Class 11 Chemistry Practical

Micro-chemical methods are available for several of the practical experiments. Wherever possible such techniques should be used.

A. Basic Laboratory Techniques
1. Cutting glass tube and glass rod
2. Bending a glass tube
3. Drawing out a glass jet
4. Boring a cork

B. Characterization and Purification of Chemical Substances
1. Determination of melting point of an organic compound.
2. Determination of boiling point of an organic compound.
3. Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid.

C. Experiments based on pH

1. Any one of the following experiments:

• Determination of pH of some solutions obtained from fruit juices, solution of known and varied concentrations of acids, bases and salts using pH paper or universal indicator.
• Comparing the pH of solutions of strong and weak acids of same concentration.
• Study the pH change in the titration of a strong base using universal indicator.

2. Study the pH change by common-ion in case of weak acids and weak bases.

D. Chemical Equilibrium
One of the following experiments:

1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of either of the ions.
2. Study the shift in equilibrium between [Co(H₂O)₆] ²⁺ and chloride ions by changing the concentration of either of the ions.

E. Quantitative Estimation
i. Using a mechanical balance/electronic balance.
ii. Preparation of standard solution of Oxalic acid.
iii. Determination of strength of a given solution of Sodium hydroxide by titrating it against standard solution of Oxalic acid.
iv. Preparation of standard solution of Sodium carbonate.
v. Determination of strength of a given solution of hydrochloric acid by titrating it against standard Sodium Carbonatesolution.

F. Qualitative Analysis
1) Determination of one anion and one cation in a given salt
Cations‐ Pb²⁺, Cu²⁺, As³⁺, Al³⁺, Fe³⁺, Mn²⁺, Ni²⁺, Zn²⁺, Co²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺, NH₄ ⁺
Anions – (CO₃)^2‐ , S^2‐, NO₂^‐ , SO₃^2‐, SO^2‐ , NO ^‐ , Cl^‐ , Br^‐, I‐, PO₄^3‐ , C₂O²‐ ,CH₃COO^‐
(Note: Insoluble salts excluded)

2) Detection of ‐ Nitrogen, Sulphur, Chlorine in organic compounds.

G) PROJECTS
Scientific investigations involving laboratory testing and collecting information from other sources.

A few suggested projects are as follows:

• Checking the bacterial contamination in drinking water by testing sulphide ion
• Study of the methods of purification of water.
• Testing the hardness, presence of Iron, Fluoride, Chloride, etc., depending upon the regional
  variation in drinking water and study of causes of presence of these ions above permissible
  limit (if any).
• Investigation of the foaming capacity of different washing soaps and the effect of addition of
  Sodium carbonate on it.
• Study the acidity of different samples of tea leaves.
• Determination of the rate of evaporation of different liquids Study the effect of acids and
  bases on the tensile strength of fibres.
• Study of acidity of fruit and vegetable juices.

Note: Any other investigatory project, which involves about 10 periods of work, can be chosen with the approval of the teacher.

Practical Examination for Visually Impaired Students of Class 11

Below is a list of practicals for the visually impaired students.

A. List of apparatus for identification for assessment in practicals (All experiments)
Beaker, tripod stand, wire gauze, glass rod, funnel, filter paper, Bunsen burner, test tube, test tube stand,
dropper, test tube holder, ignition tube, china dish, tongs, standard flask, pipette, burette, conical flask, clamp
stand, dropper, wash bottle
• Odour detection in qualitative analysis
• Procedure/Setup of the apparatus

B. List of Experiments A. Characterization and Purification of Chemical Substances
1. Crystallization of an impure sample of any one of the following: copper sulphate, benzoic acid
B. Experiments based on pH
1. Determination of pH of some solutions obtained from fruit juices, solutions of known and varied
concentrations of acids, bases and salts using pH paper
2. Comparing the pH of solutions of strong and weak acids of same concentration.

C. Chemical Equilibrium
1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing
the concentration of eitherions.
2. Study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the
concentration of either of the ions.

D. Quantitative estimation
1. Preparation of standard solution of oxalic acid.
2. Determination of molarity of a given solution of sodium hydroxide by titrating it against standard
solution of oxalic acid.

E. Qualitative Analysis
1. Determination of one anion and one cation in a given salt
2. Cations – NH+4
Anions – (CO3)2-, S2-, (SO3)2-, Cl-, CH3COO-
(Note: insoluble salts excluded)
3. Detection of Nitrogen in the given organic compound.
4. Detection of Halogen in the given organic compound.

Note: The above practicals may be carried out in an experiential manner rather than recording observations.

We hope students must have found this information on CBSE Syllabus useful for their studying Chemistry. Learn Maths & Science in interactive and fun loving ways with ANAND CLASSES (A School Of Competitions) App/Tablet.

Frequently Asked Questions on CBSE Class 11 Chemistry Syllabus

Q1

How many units are in the CBSE Class 11 Chemistry Syllabus?

There are 9 units in the CBSE Class 11 Chemistry Syllabus. Students can access various study materials for the chapters mentioned in this article for free at ANAND CLASSES (A School Of Competitions).

Q2

What is the total marks for practicals examination as per the CBSE Class 11 Chemistry Syllabus?

The total marks for the practicals as per the CBSE Class 11 Chemistry Syllabus is 30. It includes volumetric analysis, content-based experiment, salt analysis, class record, project work and viva.

Q3

Which chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry?

The organic chemistry chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry.