Question

Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer 1

Helium and neon:

• The elements having completely filled valence shells are unreactive or of extremely low reactivity and present in group 18 of the periodic table.
• Helium and neon are the 18th group elements (noble gas family).
• The atomic number of $\mathrm{He}$ is 2 and the electronic configuration is $1{\mathrm{s}}^2$.
• Here the valence shell of helium has 2 electrons in it, which means completely filled.
• The atomic number of $\mathrm{Ne}$ is 10 and the electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^6$.
• Here the valence shell of neon has 8 electrons in it, which means completely filled.
• Hence, both helium and neon atoms have in common that both have completely filled valence shells and both are in the same group.