(solved)Question 3.22 of NCERT Class XI Chemistry Chapter 3

What is the basic difference between the terms electron gain enthalpy and electronegativity?

Categories | About Hoven's Blog

Parveen,

Question 3.22
NCERT Class XI Chemistry

What is the basic difference between the terms electron gain enthalpy and electronegativity?

Solution in Detail
(video solution below this)

Difference 1: Purpose

Electronegativity is a qualitative measure of the ability of an atom to attract the shared electrons of a chemical bond.

But electron gain enthalpy is a quantitative measurement of the enthalpy change that takes place when an electron is added to an isolated atom in gaseous state.

Difference 2: Constant or not

Electronegativity is not constant for an element. It depends on the other participating elements. It is a property of an atom "in a molecule".

NOTE: But we find that the data shows a single value for electronegativity. Then how can we say that it is NOT constant? Actually, the calculated and tabulated value is meant as an indicator of the property in a wide variety of molecules. Pauling scale has a relative error of an order of 10% but can be used to get a rough qualitative idea for of any molecule.

on the other hand, electron gain enthalpy, being a property of an isolated atom in gaseous state, is a fixed constant.

Difference 3: Measurability

Electronegativity is not a measurable quantity. Mulliken calculated on the basis of absolute values of ionization enthalpy and electron gain enthalpy. Pauling calculated it on the basis of ionic resonance energies [0.79 caesium to 3.98 florine].

Electron gain enthalpy, however, is measurable.

Difference 4: Sign

Electronegativity is a positive number less than 4.0 on Pauling scale.

Electron gain enthalpy is positive for an endothermic process and negative for an exothermic process.

Difference 5: Units

Electronegativity is a dimensionless quantity with no units. It is a number.

Electron gain enthalpy has the units of energy and expressed in kJ/mol.

Examples

Florine F is the most electronegative of all the elements.

Chlorine Cl has the most negative electron gain enthalpy.

Video Explanation

Please watch this youtube video for a quick explanation of the solution:

Creative Commons License
This Blog Post/Article "(solved)Question 3.22 of NCERT Class XI Chemistry Chapter 3" by Parveen is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.