Question

As the atomic number of halogens increases, the halogens:
(A) Lose the outermost electron less readily
(B) Become lighter in colour
(C) Becomes less dense
(D) Gain electrons less readily

Answer 1

Hint: Group \[{{17}^{th}}\]is known as a group of halogens. Now, down the group, the atomic number of halogens increases, and thus size also increases, and nuclear charge decreases because of the addition of an electron in the same orbital. Down the group ionisation energy (I.E) decreases (energy required to release electrons from the outermost orbital of an isolated gaseous atom) as the electron is farther from the nucleus.

Complete Step by Step Solution:
Along the period electrons are added to the same orbital as before and on the other hand, nuclear charge also increases as the number of electrons increases. As an electron is added to the same orbital thus attraction of the nucleus becomes more on every electron (effective nuclear charge increases). Down the group, the nuclear charge increases the same as the number of electrons increases. But electrons are added to the new orbital. Due to this effective nuclear charge on every electron decreases and thus, the size of the atom increases.

Due to increases in the size of the atom down the group, the requirement of energy to release electrons from the last element of the group is less (ionisation energy decreases down the group). As the last element of the group easily releases electrons thus we can say it has less affinity (love) towards electrons and thus its electronegativity (tendency to attract bond electrons towards itself) decreases.

So, down the group electronegativity decreases and thus, has less tendency to gain or attract electrons toward itself.
Thus, the correct option is D.

Note: Down the group electronegativity decreases, so it can easily lose outermost electrons readily and become dense more easily. As ionisation energy decreases down the group, electrons are easily excited to higher energy levels, and volume increases. Due to the large size of an atom, a large number of shells absorb more radiation and start to become darker down the group.