Question

${{H}_{2}}S$ is a gas while ${{H}_{2}}O$ is liquid. Why?

Answer 1

Formation of hydrogen bonds with an attractive intermolecular force due to dipole-dipole interaction between a highly electronegative atom and a hydrogen atom. This hydrogen bonding in molecules causes changes in their melting point, boiling point, solubility, viscosity and surface tension, etc.

Complete step by step answer:
When a hydrogen atom is linked to a highly electronegative atom, it attracts pair electrons to become slightly negative and others slightly positive. A weak bond is formed between the negative end and a positive end of the other is called a hydrogen bond.
There are two types of hydrogen bonding.
(1) Intermolecular hydrogen bonding: this will occur between two separate molecules in a substance. For example, $N{{H}_{3}},{{H}_{2}}O$ molecules.
(2) Intramolecular molecules: this hydrogen bonding will occur within one single molecule. For example, ethylene glycol
The hydrogen atom is linked to two electronegative atoms simultaneously due to hydrogen bonding, which is one by a covalent bond and another one by a hydrogen bond.
The result of hydrogen bonding in compounds shows abnormally high melting points and boiling points because there is extra energy needed to break these hydrogen bonds.
For example, due to this hydrogen bonding ${{H}_{2}}O$ is a liquid whereas ${{H}_{2}}S,{{H}_{2}}Te,{{H}_{2}}Se$ are all gases at ordinary temperatures because hydrogen bonding causes linkages in water molecules to increase the boiling point of water than other compounds.
Hence, due to hydrogen bonding ${{H}_{2}}S$ is a gas while ${{H}_{2}}O$ is liquid.

Note: Carboxylic acids exist as dimers due to hydrogen bonding. There is an abnormality in the molar mass of such compounds that experimental molar mass is greater than the calculated molar mass. HF does not give the difluoride ion instead of fluoride ion due to hydrogen bonding in HF and HCl, HBr, and HI do not form hydrogen bonding.