Monday, June 20, 2011

Trends in Electron Affinity

On moving along the period, the atomic size decreases and hence electron affinity increases due to greater attraction for incoming electron. However, some irregularities are observed in a general trend. These are mainly due to the stable configurations of certain elements. Some important features of electron affinity are;
¤  Halogens have highest Electron affinity 
The electron affinity of halogens are the highest in their respective periods. This is due to small size and greater effective nuclear charge. They also need only electron to attain noble gas configurations. Thus, they have maximum tendency to accept an additional electron.
¤  Noble gases have zero Electron affinity
Noble gases have stable electronic configuration and hence they have no tendency to accept an electron. So, they have zero electron affinity.
¤  Electron affinity of Be, Mg are almost zero
Electron affinities of Be, Mg etc. are almost zero. This is because of the fact that their electronic configurations are stable because all the electrons are paired.
¤  Electron affinity of N & P are extremely low
Electron affinity of group 15 i.e. N, P etc. have electron affinity quite low, due to stable half -filled electronic configuration. 
On moving down the group the atomic size decreases and hence the incoming electron feels less attraction. Thus, electron affinity decreases down the group.
However in halogens, electron affinity of fluorine is smaller than chlorine. According to size Flourine should have higher value of electron affinity than chlorine. This is due to its small size. As a result of small size the repulsions among electrons in valence shell are relatively larger as compared to chlorine. This means that incoming electron in fluorine atom finds less attraction than that in chlorine atom. Consequently, electron affinity of chlorine is higher than flourine.


  1. Wow really very helpful keep it up

  2. Here it is written both across the period and down the group atomic size decreases. Doesn't it increase across the period and decrease down the group.

  3. It is wrongly mentioned here that atomic size decreases down the group. The correct answer is- atomic size increases down the group.