Question

Hydrogen bonding is seen in $H_{2}O$ and not in $H_{2}S$ . Why?

Answer 1

Hint: Molecules can be formed by the combination of atoms through bonding. These bonding are of different types like an ionic bond, covalent bond, and hydrogen bonding. Generally, hydrogen bonding is seen in between the molecules consisting of one least electronegative and more electronegative atom.

Complete answer:
Electronegativity is defined as the tendency of attraction of a shared pair of electrons towards itself. Electronegativity increases across the period and decreases down the group. The most electronegative element in the periodic table is fluorine which was followed by oxygen and nitrogen.
Hydrogen bonding is defined as the bond that was formed between the hydrogen atom and the other two electronegativity atoms.
Oxygen has the electronegativity of $3.44$ , hydrogen has the electronegativity of $2.2$ . Thus, in the case of water molecules, hydrogen will be present in between the two oxygen atoms and involves hydrogen bonding.
Sulphur has the electronegativity of $2.58$ , hydrogen has the electronegativity of $2.2$ . In the case of hydrogen sulphide molecules, there is not much difference in the values of electronegativity. Thus, there is no formation of hydrogen bonding in the case of hydrogen sulphide.
Thus, hydrogen bonding is seen in $H_{2}O$ and not in $H_{2}S$ due to the low electronegativity values of sulphur.

Note:
Due to the presence of hydrogen bonding in water molecules, the boiling point of water $\left(H_{2}O\right)$ is very much higher compared to the boiling point of hydrogen sulphide $\left(H_{2}S\right)$ though oxygen and sulphur belong to the same group of elements.