How do the following properties change in group - 1 and in the third period? Explain with example.
(c ) EA

Explanation

Electron Affinity : As we move down the group - 1 elements atomic radius increases gradually. Due to this reason the attraction between the added electron and the nucleus decreases. Hence electron affinity decreases from Li to Cs.
In the 3rd period while we are moving from left to right the atomic radius decreases and effective nuclear charge increases gradually. So the attraction between added electron and the nucleus increases gradually. Hence electron affinity increases from Na to Cl with certain exceptions.