Question

Explain -$H_{2}O$ is a liquid but $H_{2}S$ is a gas.

Answer 1

Hint: Oxygen and Sulphur belong to the 16th group of the modern periodic table. The electronegativity of oxygen and Sulphur is an important factor in deciding the state of compounds formed. Also check which compound shows strong hydrogen bonding. The atom that possesses strong hydrogen bonds will exist in liquid state and the latter will exist in gaseous state.

Complete step-by-step answer:
Water is a polar inorganic compound that is tasteless, odourless and almost colourless at room temperature. Water is considered as the universal solvent as many solutes readily dissolve in water. It is the most abundant substance of earth.
Water exists in a liquid state of matter at 298 K which is considered as room temperature.
Hydrogen sulphide is the chemical compound having the molecular formula $H_{2}S$. It is a colourless chalcogen hydride gas having the characteristic smell of rotten eggs. It is a highly corrosive and poisonous substance which is easily flammable.
Hydrogen sulphide is slightly denser than air. A mixture of hydrogen sulphide and air can be highly explosive. It acts as a reducing agent especially in presence of its conjugate base.
Hydrogen sulphide exists as a gas at 298 K temperature.
Water exists as a liquid however hydrogen sulphide exists as a gas because there is strong hydrogen bonding between the water molecules due to high electronegativity of oxygen atom. However, the extent of hydrogen bonding is not considerable as the electronegativity of sulphur atoms is less.


Note: The elements of group 16 especially oxygen and sulphur are called chalcogens. This is because previously most copper ores existed in the form of oxides or sulphides of copper.