Question

Ionisation potential of elements on moving down a group:
(A) increases
(B) decreases
(C) constant
(D) none of these

Answer 1

Hint: You need to have a clear understanding of ionization potential. Pick a group of your choice and observe the trends in ionization potential by keeping in mind the effective nuclear charge and radius of the atom.

Complete step by step solution:
Ionisation Energy also called ionization potential is the amount of energy required to remove an electron from an isolated atom.
- Isolated conditions mean that there will be no interference of physical conditions as well as of the neighbouring atoms.
- There is ionization energy for each successive electron removed.
- The difference in ionization energy for removal of electrons is used to find the valency of the given atom.
- Ionisation energy is expressed in joules or electron volts and is measured in an electric discharge tube.
- Alternatively, ionisation energy is defined as a measure of the capability if an element to take part in a chemical reaction that requires ion formation or donation of electrons,
- As we move down the group, we observe that the radius of the atom increases. Due to this the electrons become far apart from the nucleus.
-Since the effective nuclear charge decreases, we see that lesser energy is required to remove an electron from its outermost orbit as we move down the group.
From this, we can conclude that ionization potential decreases as we move down the group.

Therefore, the correct answer is option (B).

Note: Do not get confused between the terms, ionization energy and ionization potential as they are synonymous to each other and either one of them can be used. In this question, we are comparing only the first ionization potential of the elements in a group.