Question

Give reasons for the following:
${H_2}O$ is a liquid and ${H_2}S$ is a gas.

Answer 1

We can see that in case of water there is presence of oxygen which has high electronegativity, which can be the reason for being water.

Complete step by step answer:
At room temperature, if we see ${H_2}O$ is a liquid because there is presence of oxygen which is highly electronegative and due to this hydrogen atoms from other molecules of water will form hydrogen bonds with oxygen which will be resulting in intermolecular hydrogen bonding.
In ${H_2}S$, sulphur is less electronegative as compare to the oxygen and hence $S - H$ bond will be much less polar than the $O - H$ bond and there will be no hydrogen bonding in ${H_2}O$, it will have weak Van Der Wals forces between its molecules. So, ${H_2}S$ exists as gas.
So, we can see that the molecule of ${H_2}O$ is strongly packed because intermolecular hydrogen bonding is associated with this and hence it is liquid whereas molecules of ${H_2}S$ gas is not that strongly packed because they are held together with weak Van Der Wals forces and hence it is a gas at room temperature.

Note: Only fluorine, oxygen and nitrogen are capable of hydrogen bonding in compounds like $F - H$ , $O – H$ and $N - H$ bonds which is ultimately a very strong bond.

We can depict that if the forces between the molecules are strong then they will be more closely bonded with each other which is in the case of ${H_2}O$ and also, if the forces between the molecules are weak then they will be apart which is in the case of ${H_2}S$.