Question

Mention the first five elements of the periodic table having even atomic numbers. Logically choose the one with the maximum ionisation energy and explain your logic.

Answer 1

• The elements in the periodic table are arranged in the increasing order of their atomic numbers.
• The first five elements with even atomic numbers in the periodic table are:

Element	Helium $\left(\mathrm{He}\right)$	Beryllium $\left(\mathrm{Be}\right)$	Carbon $\left(\mathrm{C}\right)$	Oxygen $\left(\mathrm{O}\right)$	Neon $\left(\mathrm{Ne}\right)$
Atomic Number	2	4	6	8	10

• Helium, Beryllium, Carbon, Oxygen, and Neon are the first five elements of the periodic table with even atomic numbers.
• Helium and Neon are the noble gases, Beryllium comes under alkaline earth metals, and Carbon and Oxygen are the non-metals. Except for Helium, the other four elements are in the second period of the periodic table.
• Ionization energy is the energy required to remove an electron from the valence shell of an atom.
• In the periodic table, ionization energy increases along the period (from left to right) and decreases along with the group (from top to bottom).
• Ionization energy increases across the period because the electrons are held tighter by the higher nuclear charge.
• So the element at the top corner has the maximum ionization energy.
• Helium has maximum ionization energy because it is present at the right end of the periodic table (Period 18 and Group 1).

Hence, Helium$\left(\mathrm{He}\right)$ is an element with the maximum ionization energy along with these elements having even atomic numbers.