Question

why electron gain enthalpy becomes more negative from left to right in a period and becomes positive from up to down in a group????​

Answer 1

Answer:

variation in a group:- in general the electron gain enthalpy become less negative as we move down a group.this may be explained as follows

as we move down a group both atomic size and the nuclear charge increases. Buy the effect of increase in atomic size is much more pronounced than the nuclear charge. Thus with increase in atomic size the attraction of the nucleus for the incoming electron decreases and hence the electron gain enthalpy become less negative.

variation in period:- in general electron gain enthalpy become more and more negative from left to right in a period.this may be explained as follows

as we move across the period from left to right the atomic size decreases and the nuclear charge increases. Both the factors tend to increase the attraction by the nucleus for the incoming electron and hence electron gain enthalpy, in general, become more and more negative in a period from left to right.