Electronegativity, definition, explanation, examples, Significance and factors

Electronegativity definition

The tendency of an atom to attract a shared pair of electrons toward itself is called electronegativity.

Explanation of Electronegativity

Electronegativity is a measure of an atom’s ability to attract and hold electrons in a chemical bond. It is a fundamental property that influences the nature of bonding in molecules. Linus Pauling introduced the concept and devised a scale to quantify electronegativity values for elements.

Higher electronegativity values indicate a stronger pull on electrons, leading to the formation of polar bonds and contributing to the overall reactivity of an element in various chemical reactions. The scale ranges from 0.7 for elements with low electronegativity, such as cesium, to 4.0 for highly electronegative elements like fluorine. Electronegativity has no units.

Electronegativity is a fundamental concept in chemistry that helps us understand the ability of an atom to attract and hold onto electrons in a chemical bond. First introduced by Linus Pauling, electronegativity plays a crucial role in predicting the nature of chemical bonds, the polarity of molecules, and the overall reactivity of elements.

Consider the formation of a covalent bond between two similar atoms of a molecule like H2. In this molecule, the electron pair participating in the formation of a covalent bond is shared equally by both hydrogen atoms. On the other hand, consider the covalent bond formation between two dissimilar atoms of a molecule like HCl. In this molecule shared pair of electrons is not shared equally.

This unequal sharing is due to the fact that the Cl atom has a greater tendency than the H atom to attract shared electron pairs between them.

Examples

Symbol	Element Name	Atomic Number	Electronegativity (Pauling)
H	Hydrogen	1	2.2
C	Carbon	6	2.55
N	Nitrogen	7	3.04
O	Oxygen	8	3.44
F	Fluorine	9	4.00
Na	Sodium	11	0.93
Mg	Magnesium	12	1.31
Al	Aluminum	13	1.61
Si	Silicon	14	1.90
P	Phosphorus	15	2.19
S	Sulfur	16	2.58
Cl	Chlorine	17	3.16
K	Potassium	19	0.82
Ca	Calcium	20	1.00
Br	Bromine	35	2.96
I	Iodine	53	2.66

How to calculate Electronegativity?

Example 1: Calculating Electronegativity of Hydrogen (H)

Given: Pauling electronegativity of hydrogen (XH​) = 2.2

The electronegativity of hydrogen is simply its Pauling electronegativity value, which is 2.2.

Example 2: Calculating Electronegativity of Oxygen (O)

Given: Pauling electronegativity of oxygen (XO​) = 3.44

The electronegativity of oxygen is 3.44 according to the Pauling scale.

Example 3: Calculating Electronegativity Difference in a Bond

Given: Pauling electronegativity of chlorine (XCl​) = 3.16, and hydrogen (XH​) = 2.2

The electronegativity difference (ΔX) between chlorine and hydrogen is calculated as follows:

ΔX= XCl​ − XH​

ΔX=3.16−2.2=0.96

Steps to Calculate Electronegativity

Identify the Electronegativity Values

Obtain the Pauling electronegativity values for the elements involved in the calculation.

Apply the Electronegativity Scale

For individual elements, the electronegativity is simply the Pauling electronegativity value of that element.

Calculating Electronegativity Difference (if applicable)

In the case of a bond, subtract the electronegativity of the less electronegative element from that of the more electronegative element to find the electronegativity difference.

Significance of Electronegativity

Chemical Bonding

Electronegativity is crucial in predicting the type of chemical bond formed between elements. Large differences in electronegativity often lead to ionic bonds, while smaller differences result in covalent bonds.

Polarity of Molecules     

In molecules with polar covalent bonds, the electronegativity difference between the atoms creates a dipole moment, resulting in overall molecular polarity.

Reactivity of Elements

Elements with higher electronegativity values are more likely to gain electrons and form negative ions, while elements with lower electronegativity values are more likely to lose electrons and form positive ions.

Factors Influencing Electronegativity

Nuclear Charge

The greater the positive charge in the nucleus, the stronger the pull on electrons. Electronegativity tends to increase with an increase in nuclear charge.

Atomic Size

Electronegativity generally decreases as you move down a group due to the larger atomic size. Larger atoms have electrons farther from the nucleus and are less effective at attracting electrons.

Electron Shielding

Inner electron shells shield outer electrons from the full effect of the nucleus. Effective shielding reduces the attractive force on outer electrons, influencing electronegativity.

Periodic Trend of Electronegativity

Variation of electronegativity in groups

Electronegativity decreases from top to bottom in a group.

The increase in atomic size and the presence of additional electron shells contribute to reduced electronegativity.

Variation of electronegativity in a periods

Electronegativity values increase from left to right in the periods.

This trend is associated with the increasing effective nuclear charge as electrons are added to the same energy level.