Question

Why does hydrogen occur in a diatomic form rather than in monoatomic form under normal condition?

Answer 1

Hint: Diatomic molecules are composed of two atoms. These two atoms can be of the same element (as in the case of homonuclear molecules) or from the other elements (as in the case of heteronuclear molecules). Hydrogen shows the properties of both Group $1$ and Group ${\text{17}}$.

Complete step by step answer: A single atom of hydrogen is in monatomic form and it has electronic configuration of $1{s^1}$. This means that one electron of the monatomic hydrogen will be in ${\text{1s}}$ orbital. The ${\text{1s}}$ orbital can accommodate a maximum of two electrons. So, in monatomic hydrogen, the orbital is half filled. But full filled orbitals are more stable than half filled orbitals because of the principle of symmetry (fully filled orbital is more symmetrical) and exchange energy (fully filled orbital has more exchange energy). So, hydrogen atom will share its one electron with another hydrogen atom to form a covalent bond, and this leads to the formation of the stable diatomic hydrogen molecule. The $1{s^1}$ electronic configuration is a complete octet configuration which is stable in nature and also with this configuration hydrogen acquires the nearest noble gas electronic configuration.
So, Hydrogen occurs in a diatomic form rather than in monoatomic form under normal condition.

Note: Though hydrogen has es1 electronic configuration is placed in group ${\text{1}}$ of the periodic table but it has the tendency to form diatomic molecules, which is the property of Halogens of group ${\text{17}}$. This leads to the anomalous position of hydrogen in the periodic table.