Electronegativity

Introduction

Electronegativity is a measure of an atom’s attraction to bonding electrons in molecules in comparison to other atoms. Linus Pauling, an American chemist, developed electronegativity values that range from slightly less than one for alkali metals to a maximum of four for fluorine. Large electronegativity values indicate a greater attraction for electrons than low electronegativity values. Elements with large electronegativity differences tend to form ionic compounds, which are made up of positively and negatively charged units called ions; elements with moderate electronegativity differences form polar, covalent compounds, in which atoms are held together by chemical bonds but show some degree of ionisation; and elements with nearly equal electronegativity differences form nonpolar compounds, which have little charge separation.

Electronegativity Definition

Electronegativity is described as an element’s or atom’s proclivity to attract bonding pairs of electrons towards itself. It also describes an atom’s ability to remove electron density when a covalent link is created. It is one of the elements’ periodic qualities. This means that the elements are organised in the periodic table in such a way that their chemical and physical characteristics follow a predictable pattern. Electronegativity is determined by the electron affinity and ionisation energy of an atom. These two qualities reflect how tightly an atom maintains its own electrons and how strongly it attracts other electrons. Across the periodic table, electronegativity rises from left to right (metals to nonmetals). The electronegativity of the s and p block members rises as you move up the group. And if we will see in the modern periodic table Fluorine is the most electronegative element in that.

Periodic Trend

Electronegativity, like electron affinity, atomic/ionic radius, and ionisation energy, follows a clear pattern on the periodic table.

Across a period, electronegativity normally rises from left to right. The noble gases are usually exceptions to this rule. 

Electronegativity often decreases as one moves down the periodic table.That is because of the increased distance between the nucleus and the valence electron.

Electronegativity and ionisation energy follow the same periodic table trend. Elements that have low ionisation energies tend to have low electronegativities. However these atom’s nuclei never exert a strong pull on electrons. 

Similarly, elements that have high ionisation energies tend to have high electronegativity values. Electrons are strongly attracted to the atomic nucleus.

Factors affecting Electronegativity

1. Atomic size

The larger the atomic size of the element in the periodic table, the lower electronegativity will be. Because of the rise in shell number, the electrons are further away from the nucleus and feel less nuclear force of attraction. As a result, the electronegativity values will be lower.

2. Hybridization

The higher the s-character of the hybrid orbital, the higher the electronegativity value.

We have a 25% s-character in sp3 hybridization.

In sp2 hybridization, we have 33.3 percent s-character.

In sp hybridization, we have 50% s-character, 

Hence the ascending order of electronegativity values is: sp3 < sp2 < sp

3. Nuclear charge

The number of protons in an atom’s nucleus determines the effective nuclear charge (Z).

A higher nuclear charge results in a higher electronegativity value.

This occurs because the nucleus attracts electrons closer to itself.

4. Substituent Effect

The electronegativity of an atom is determined by the type of the substituent linked to that atom. For example, the carbon atom in CF3I receives a higher positive charge than the carbon atom in CH3I. As a result, the C-atom in CF3I is more electronegative than the C-atom in CH3I.The variation in electronegativity of an atom produced by substituents leads to a change in its chemical behaviour.

Most and Least Electronegative in Periodic Table

If we will go through the periodic table the Fluorine is the most electronegative element with the electronegativity of 3.98. Cesium is the least electronegative element (0.79). Because electropositivity is the inverse of electronegativity, cesium is the most electropositive element. It should be noted that earlier texts identify both francium and cesium as having the lowest electronegativity value of 0.7, however the value for cesium was experimentally corrected to 0.79. There is no experimental evidence for francium, although its ionisation energy is larger than that of cesium, hence francium is projected to be somewhat more electronegative.

Conclusion 

Electronegativity is a measure of an atom’s attraction to bonding electrons in molecules in comparison to other atoms. Electronegativity is determined by the electron affinity and ionisation energy of an atom. The electronegativity of the s and p block members rises as you move up the group. The larger the atomic size of the element in the periodic table, the lower electronegativity will be.The higher the s-character of the hybrid orbital, the higher the electronegativity value will be. The electronegativity of an atom is determined by the type of the substituent linked to that atom. The variation in electronegativity of an atom produced by substituents leads to a change in its chemical behaviour. Fluorine is the most electronegative element with the electronegativity of 3.98.