Question

What family of elements is relatively unreactive and why?

Answer 1

Hint: Reactivity of elements is due to the fact that they have valence or free electrons in their outer shell. The outer shell is also called the valence shell. The reactivity of elements depends on the number of electrons in this valence shell, and their configuration having fully or partially filled orbitals.

Complete answer:
A chemical reaction results in the atoms being attached or bonded into a molecule forming the product. This chemical reaction is a result of the reactivity of the elements that take part in that reaction. The reactivity of elements is due to the presence of electrons in their outer or valence shell.
Elements with only one or two electrons in their outer shell are considered to be highly reactive, this is due to the fact that the forces that the nucleus exert bind the electrons that are fully filled in their orbitals, while the outer shell electrons does not get affected by this force, so they result in weaker forces, that makes them easier to get transferred to another atom, and hence reacting.
Same is the case, where elements have only one or two electrons missing from their outer shell. They readily take up the electrons from the reactive atoms and form a new molecule.
These reactions take place, when any atom wants to achieve noble gas configuration by completing its octet, which is 8 electrons in the valence shell. So, further they cannot react if they have 8 electrons.
As we know, noble gases are the elements that contain all the 8 electrons in their valence shell, and are considered as fully filled in their configuration. It is due to this reason, that noble gases from group 18 are the family of unreactive elements. They do not have any electron to donate, or to take up in order to complete their octet, as they have a complete octet. For example, argon gas has a configuration, $[Ne]\,3{{s}^{2}}3{{p}^{6}}$ , and electrons filled as, 2, 8, 8 in per shell. So, it has all electrons filled in the shells and orbitals, making it unreactive.
So, the noble gases are the family of unreactive elements due to fully filled electronic configuration.

Note:
The shells in an atom are, K, L, M, N, that can accommodate, 2, 8, 18 and 32 electrons respectively. The more subatomic quantity is the orbitals, s, p, d, and f that can have 2, 6, 10 and 14 electrons respectively. The noble gases are helium, neon, argon, krypton, and xenon. They have all of these shells and orbitals fully filled.