Electronegativity – Definition, Periodic Trends, Effect on Bonding, FAQs on Electronegativity

February 11, 2025December 12, 2024 by Neeraj Anand, Param Anand

What is Electronegativity?

The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity.

It is a dimensionless property because it is only a tendency. It basically indicates the net result of the tendencies of atoms in different elements to attract the bond-forming electron pairs. We measure electronegativity on several scales. The most commonly used scale was designed by Linus Pauling.

According to this scale, fluorine is the most electronegative element with a value of 4.0 and cesium is the least electronegative element with a value of 0.7.

Periodic Trends in the Electronegativities of Elements

As we move across a period from left to right the nuclear charge increases and the atomic size decreases, therefore the value of electronegativity increases across a period in the modern periodic table.

For example, the electronegativity trend across period 3 in the periodic table is depicted below.

The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity.

There is an increase in the atomic number as we move down the group in the modern periodic table. The nuclear charge also increases but the effect of the increase in nuclear charge is overcome by the addition of one shell. Hence, the value of electronegativity decreases as we move down the group. For example, in the halogen group as we move down the group from fluorine to astatine the electronegativity value decreases and it is shown in the diagram below.

It is a general observation that metals show a lower value of electronegativity as compared to the non-metals. Therefore, metals are electropositive and non-metals are electronegative in nature. The elements in period two differ in properties from their respective group elements due to the small size and higher value of electronegativity.

The elements in the second period show resemblance to the elements of the next group in period three. This happens due to a small difference in their electronegativities. This leads to the formation of a diagonal relationship.

Most and Least Electronegative Elements

Fluorine is the most electronegative element on the periodic table. Its electronegativity value is 3.98. Cesium is the least electronegative element. Its electronegativity value is 0.79. Electro positivity is the exact opposite of electronegativity, therefore, we can say that Cesium is the most electropositive element.

Those elements requiring only a few electrons to complete their valence shells, and having the least quantity of inner electron shells between the positive nucleus and the valence electrons, are the most electronegative. The most electronegative of all elements is fluorine. Its electronegativity is 4.0. Metals have electronegativities less than 2.0. The least electronegative elements are cesium (Cs) and francium (Fr), with electronegativity values of 0.7.

Therefore,

Fluorine is the most electronegative element and cesium is the least electronegative element.

Impact of Electronegativity on Covalent Bonding

The strength of a covalent bond is highly dependent on the electronegativities of the two bonded atoms (especially the difference in the electronegativities of the bonded atoms). Homonuclear diatomic molecules feature relatively ‘pure’ covalent bonds since the electronegativities of the bonded atoms are the same (resulting in the bonded pair of electrons being almost equidistant from the two bonded nuclei). Examples of such covalent bonds can be seen in H₂ molecules, Cl₂ molecules, and O₂ molecules.

On the other hand, the covalent bonds between two species of varying electronegativities tend to become polarized. This occurs because the more electronegative atom pulls the bond pair of electrons closer to itself, developing a partially negative charge in the process (which is usually denoted by the symbol 𝛿-). At the same time, the more electropositive atom develops a partial positive charge (denoted by 𝛿+). These partial charges are responsible for the polarity of the chemical bond.

Bonds Between Highly Electronegative and Highly Electropositive Atoms

In the covalent bonds featuring a large difference in the electronegativities of the bonded atoms, it is uncommon for the more electronegative atom to gain complete control over the bond pair of electrons, resulting in the formation of two ions. Here, the more electronegative atom forms an anion and the more electropositive atom becomes a cation.

It is important to understand that all covalent bonds between dissimilar species have some ionic character. Similarly, all ionic bonds have some covalent character as well. The ionic character of the covalent bond is determined by the difference in electronegativity. When the electronegativities of the bonded species are not very different, the bond will be more covalent than ionic. However, when there is a large enough difference in the electronegativities of the bonded atoms, the bond becomes polar enough to be considered more ionic than covalent.

Electronegativity Table

Electronegativity is a chemical property that describes the power of an atom in a molecule to attract shared-pair electrons towards itself. There is a large difference in electronegativity for atoms from the left- and right-hand sides of the periodic table. Electronegativity is an important quantity in determining the nature of bonds between elements and will be considered as the main factor in chemical bonding.

The periodic table of elements with the electronegativity table is given below.

Factors Affecting Electronegativity

1. Size of an Atom:

A greater atomic size will result in less value of electronegativity, this happens because electrons being far away from the nucleus will experience a lesser force of attraction.

2. Nuclear Charge:

A greater value of nuclear charge will result in a greater value of electronegativity. This happens because an increase in nuclear charge causes electron attraction with greater force.

3. Effect of Substituent:

The electronegativity of an atom depends upon the nature of the substituent attached to that atom. For example, the carbon atom in CF₃I acquires a greater positive charge than CH₃I. Therefore, C-atom in CF₃I is more electronegative than in CH₃I. The difference in electronegativity of an atom caused by substituents results in different chemical behaviour of that atom.

Frequently Asked Questions – FAQs

Which is the best definition of electronegativity?

Electronegativity is a function of an atom’s ability to attract an electrons binding pair. The most frequently used is the Pauling scale. Fluorine is assigned a value of 4.0, and values that are the least electronegative at 0.7 range down to cesium and francium.

What is high electronegativity?

Electronegativity decrease as it moves from top to bottom and increases over time from left to right. The most electronegative element is, therefore, fluorine, while francium is one of the least electronegative elements.

What is the electronegativity difference?

The degree to which an atom attracts electrons in a chemical bond is described by electronegativity. If the difference in electronegativity is greater than 1.7, the character of the bond will be ionic. If the difference in electronegativity is between 0.4 and 1.7, the character of the bond is polar covalent.

What is the difference between electron affinity and electronegativity?

The difference between the two is that electronegativity is a chemical property that shows how well an atom can attract electrons to itself as the amount of energy released when an electron is added to a neutral atom.

Is electronegativity a relative quantity?

Electronegativity is an example of an atom’s ability to attract electrons. It is proportional to the difference between the potential for ionization of an atom and its attraction to the electron.

How does electronegative vary along the period?

Electronegativity increases as we move left to the right in the period because as we move across the period, the effective nuclear charge increases and the atomic size decreases. Therefore, the tendency to attract shared pairs of electrons increases, thereby increasing electronegativity.

How does electronegative vary in a group?

Electronegativity decreases as we move down the group because as we move down the group, the atomic size increases and the effective nuclear charge decreases. Therefore, the tendency to attract shared pairs of electrons decreases, thereby decreasing electronegativity.

Name the most electronegative element and least electronegative element in the periodic table?

Fluorine is the most electronegative element, and caesium is the least electronegative element in the periodic table.

How does the electronegativity of an element affect its bonding?

The electronegativity of an element affects the bonding of an element. Elements with high electronegativity tend to form ionic bonds with other elements.

Q10

How does the size of an atom affect its electronegativity?

The size of an atom affects the electronegativity of an element. A greater atomic size corresponds to less value of electronegativity. Electrons being far away from the nucleus will experience a lesser force of attraction, therefore less electronegativity.

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.

Evaluation Scheme	Marks
Volumetric Analysis	08
Salt Analysis	08
Content Based Experiment	06
Project Work	04
Class record and viva	04
Total	30

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

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).

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.

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.