Question

Electron affinity depend on:
A. Atomic size
B. Nuclear charge
C. Atomic number
D. Both atomic size and nuclear charge

Answer 1

Hint: Electron affinity is a property of the nucleus which is related to its ability to attract electrons. So, if we could find what happens when more orbits are added to an atom, and compare the characteristics of similar elements along a group and period, we will get to our answer.

Complete step by step answer:
Electron affinity is the attraction of the nucleus towards its electrons, and can be measured indirectly as the amount of energy released when an electron is attached to a neutral atom or molecule in the gaseous state to form a negative ion. From common knowledge, we know that closer the electrons are to the nucleus, greater will be the electron affinity. This is because the nucleus has protons, which have positive charge and electrons are negatively charged particles, and since unlike charges attract each other, closer the electrons, greater the electron affinity. Hence, as atomic size increases, the electrons become further away from the nucleus and hence, electron affinity decreases.
Another factor which affects electron affinity is effective nuclear charge, which is defined as the positive force experienced by electrons due to the pull of the positively charged nucleus. As atomic number increases, more protons are added to the nucleus. More number of protons in the nucleus will mean more positive charge to attract the electrons, and hence, as nuclear charge increases, electron affinity increases.

Therefore, as both atomic size and nuclear charge affect electron affinity, the correct option to be marked is option D.

Note: Electron affinity increases along a period, as the effective nuclear charge increases due to addition of more protons. Atomic size doesn’t play a major role along a period as the electrons are being added to the same shell. However, down a group, electron affinity decreases as the atomic size increases for every period passed while moving down. Note that electron affinity is different from electronegativity. The former is the energy released when an electron is added to the atom while the latter is the tendency of an atom to attract the shared pair of electrons in a bond.