Question

Arrange these elements according to electron affinity.

Most energy released by gaining an electron to Most energy absorbed by gaining an electron.

Br, O, Ar

Answer 1

Electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to the neutral atom to form a negative ion in the gaseous system or in other words, it is the change in energy of a neutral atom.

In the periodic table , electron affinity varies in groups and periods.Electron affinity reduced as we proceed to down in the group.This is because ,electrons are placed in a higher energy levels far from nucleus.

In the case of noble gas or zeroth group elements, electron affinity is zero. or they not possess electron affinity,because they complete their octect. no ability to gain electron. Argon is under this group so, its electron affinity is zero.

When comes to Bromine, and oxygen. Bromine has highest EA , because it is halogen element. Propably halogens have high tendency to gain or loose electrons. Bromine EA is 324.6 KJ/Mol

In the case of Oxygen electron affinity is 141 KJ/Mol

here the incresing order of electron affinity is $Br> O> Ar$

decreasing order is  $Ar< O< Br$