Question

In the periodic table, the ionization potential in a group … from top to bottom.
A.Increases
B.Decreases
C.Does not change
D.Can not be predicted

Answer 1

Before answering this question, we should first know about ionization potential. Ionization potential or ionization energy can be defined as the estimation of the difficulty to eliminate an electron from an atom or the capability of an atom or ion to give an electron. It happens in the ground state of the atoms.

Complete answer:
The outermost electrons will face a less effective nuclear charge compared to the actual nuclear charge. It happens because the electrons that are innermost shield the electrons which are outermost by causing hindrance in the path of nuclear charge. For Example- If we consider an example of Sodium (Na), Inner electrons ($1{{s}^{2}},2{{s}^{2}},2{{p}^{6}}$) will shield the outer electron ($3{{s}^{1}}$).
The ionization energy trend in the periodic table is :
When we move from top to bottom in a group, it decreases.
When we move from left to right across a period, it increases.
To eliminate an electron from an atom needs energy in huge amounts to conquer the magnetic pull created by the positive charge of the nucleus. The I.E is always positive, As we move from left to right across a period, the ionization energy will always increase and as we move from top to the bottom, the ionization energy will decrease because the atomic number down the group increases results in the increase in the number of shells as well. The distance between the outermost electron and nucleus is so much that it can be easily removed. And as shells are increasing, the shielding effect will be more as well.

So, Option (B) decreases is correct.

Note:
Factors that affect the ionization energy are :
Two factors are responsible -
The force of attraction between the nucleus and electrons.
The force of repulsion between the electrons.