Electronegativity - Overview, Factors, Elements, Applications, FAQs

Electronegativity

The tendency of an atom to attract the shared pair of electrons towards itself is called electronegativity. It is a relative quantity. This concept was introduced in 1932 by Pauling. It has no units. Fluorine is the most electronegative element known so far and its value is arbitrarily assigned as 4.0. In moving from left to right in a period, the electronegativity increases while in moving from the top to bottom in a group, the electronegativity decreases.

Factors Affecting Electronegativity

Several key influences determine an atom’s electronegativity:

First, as atomic size increases, electronegativity declines because outer electrons are farther from the nucleus and less strongly attracted .

Next, a higher effective nuclear charge—due to more protons or reduced shielding—boosts electronegativity by increasing the nucleus’s pull on valence electrons.

Lastly, an element’s oxidation state affects its electronegativity. Atoms in higher oxidation states have fewer electrons shielding the nucleus and a smaller radius, so they attract bonding electrons more strongly—as seen, for instance, with Fe³⁺ being more electronegative than Fe²⁺ .

Scale for Measuring Electronegativity and Application of EN

Scales for measuring electronegativity

There are various following scales to measure the electronegativity of elements.

1. Pauling Scale: The electronegativity of the elements in Pauling scale is given by the following formula:

$M_A-M_B=0.208\left[E_{A-B}-\left(E_{A-A} \times E_{B-B}\right)^{1 / 2}\right]^{1 / 2}$

Where, E_A-B is the bond energy of A-B

E_A-A is the bond energy of A-A

E_B-B is the bond energy of B-B

This formula is used only when the energy is taken in kcal/mol.

When bond energy is taken in kJ/mol, then:

$M_A-M_B=0.102\left[E_{A-B}-\left(E_{A-A} \times E_{B-B}\right)^{1 / 2}\right]^{1 / 2}$

2. Mulliken Scale: Mulliken considered the electronegativity as the average of the ionisation potential and electron gain enthalpy of an atom.

(i) When ionisation potential and electron gain enthalpy are in taken in electron-volts:

Electronegativity = (IE + EA)/2

(ii) When ionisation potential and electron gain enthalpy are in taken in kJ/mol.

Electronegativity =(IE + EA)/(2 x 96.48)

3. Allred and Rochow Scale: In this scale, the electronegativity is given by the following formula:

Electronegativity = $0.744+\left(3590 \mathrm{Z} / \mathrm{r}^2\right)$ Where Z is the effective nuclear charge and r is the covalent radius in pm.

Related Topics Link

• Electronic Configuration of First 30 Elements
• Electron Gain Enthalpy
• Homologous Series
• Atomic radius in periodic table in basic chemistry
• Classification of Elements in Modern Periodic Table
• 118 elements, their symbols and their atomic number

Applications of Electronegativity

The following predictions can be made out of the information of electronegativities of atoms.

1. Nomenclature: The nomenclature of binary compounds can be done using the electronegativity value of the atoms. The atom with higher electronegativity is written with ide as suffix. For example, in HCl, chlorine atom has higher electronegativity, thus it is written as chloride and the complete name is hydrogen chloride.

2. Nature of Bond: From the electronegativity values of respective atoms, the nature of bond can be estimated.

(i) When the electronegativity difference between two atoms i.e, M_A- M_B = 0, then the bond is purely covalent.

(ii) When M_A- M_B is small, then the bond is polar but covalent.

(iii) When M_A- M_B is 2.1, then the bond is 50% ionic and 50% covalent.

(iv) When M_A- M_B is more than 2.1, the bond is very much ionic and less covalent.

The percentage of ionic character is given by the following formula:

Percentage of ionic character = 16(M_A - M_B) + 3.5(M_A - M_B)²

Where M_A and M_B are the electronegativities of two bonded atoms i.e, A and B.

3. Nature of Element: The elements with lower electronegativity values are metals while the elements with higher electronegativity values are non-metals. The elements with intermediate electronegativity values are metalloids. Fluorine has the highest electronegativity value, thus it is the most non-metallic element. Similarly, caesium has the lowest electronegativity value, thus it is the most metallic element.

4. Nature of Oxides: The nature of the oxides formed by the elements can also be predicted by the electronegativity. When M_O - M_A difference is lower, then the oxide is acidic in nature but when this difference M_O - M_A is large, then the oxide is basic in nature. M_O here is the electronegativity of oxygen.

5. Bond Strength: The more the electronegativity difference between the atoms, the stronger is the bond. Thus,

H-F > H-Cl > H-Br > H-I

6. Acidic Nature: When the electronegativity difference is less, then bond between the atoms is weaker and thus it is easier to lose the proton. Thus,

H-I > H-Br > H-Cl > H-F

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Some Solved Examples

Example 1: The correct option concerning the Pauling electronegativity values of the elements is :

1) Ga < Ge

2) P > S

3) Si < Al

4) Te > Se

Solution:

Electronegativity -A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons is electronegativity.- wherein It is not a measurable quantity.

Electronegativity and non-metallic character -

Non-metallic elements have a strong tendency to gain electrons. Therefore electronegativity is directly related to non-metallic properties of elements.

- wherein

Electronegativity ∝ non-metallic property
Correct order
(1) Ga<Ge
(2) Si<Al
(3) P<S
(4) Te<Se

Hence, the answer is the option (1).

Example 2: The electronegativity of an element is related to ionization energy and

1) Atomic radii

2) Electron affinity

3) Ionic radii

4) Nucleus

Solution:

The electronegativity depends upon the sum of Ionisation and Electron Affinity.

The electronegativity of any given element is not constant. It varies depending on the elements to which it is bound.

Though it is not measurable, it does provide a means to predict the nature of the force that holds atoms.

More electronegative elements will have positive Electron affinity due to electron attraction as well as more Ionisation Energy.

Hence, the answer is the option (2).

Example 3: Which of the following is the most electronegative?

1) Be

2) B

3) C

4) N

Solution:

lectronegativity generally increases across a period from left to right.

e.g. from lithium to fluorine.

N is the most electronegative element among the given elements as we move from left to right in a period, the electronegativity increases.

Hence, the answer is the option (4).

Example 4: Which one of the following elements is most electronegative?

1) Fluorine

2) Sulphur

3) Oxygen

4) Bromine

Solution: As we learned, Variation of electronegativity along group

Electronegativity generally decreases down a group in the periodic table.

- wherein

e.g. from fluorine to astatine.

Electronegativity decreases as we move down the group and increases as we move from left to right in a period.

Hence, the answer is the option (1).

Example 5: Which of the following is most electronegative?

1) Carbon

2) Silicon

3) Lead

4) Tin

Solution:

Electronegativity - The electronegativity of any element decreases down the group. Thus carbon is the most electronegative element.

Variation of Electronegativity

• In moving from top to bottom in a group the atomic size increases thus the force of attraction decreases and hence the electronegativity decreases.

• In moving from left to right in a period, the atomic size decreases and effective nuclear charge increases, thus the electronegativity increases.

• Halogens are the most electronegative elements and fluorine has the highest electronegativity.

• For transition elements, the electronegativity values vary between 1.1 to 1.3.

• Metals have lower electronegativity values while non-metals have higher electronegativity values.

Hence, the answer is the option (1).

Example 6: Two elements with electronegativities are 1.2 and 3.2 respectively, the bond formed between them will be:

1) Covalent

2) Metallic

3) Ionic

4) None

Solution:

Electronegativity - Nature of Bond: The nature of the bond can be estimated from the electronegativity values of respective atoms.

(i) When the electronegativity difference between two atoms, i.e., M_A—M_B = 0, then the bond is purely covalent.

(ii) When M_A - M_B is small, the bond is polar but covalent.

(iii) When M_A - M_B is 1.9, the bond is 50% ionic and 50% covalent.

(iv) When M_A—M_B is greater than 1.9, the bond is more ionic and less covalent.

The percentage of ionic character is given by the following formula:

Percentage of ionic character = 16(M_A - M_B) + 3.5(MA - MB)2

M_A and M_B are the electronegativities of two bonded atoms, i.e., A and B.

The electronegativity difference between the constituent atoms must be greater than 1.9 to form the ionic bond.

Hence, the answer is the option (3).

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