Hydrogen sulphide is structurally similar to water and has the same number of valence electrons. Moreover, the electronegative atoms in both molecules belong to the same group of the periodic table. Differences in their physical properties are primarily due to their different polarities (H 2 O 1.45 𝑥𝑥10 -27 cm 3 and H 2 S 3.95 𝑥𝑥10 -27 cm 3 ).