Hydrogen is the first element in the periodic table. Its atomic number is 1, and it has only one electron in its valence shell. So, it belongs to the first group and the first period of the periodic table.

Hydrogen shows dual nature because it resembles the alkali metals of Group IA and the halogens of Group VIIA.

i) Each of them can form a cation by loss of an electron.

H → H⁺ + e^-

Li →Li⁺ + e^-

ii) Both alkali metals and hydrogen act as reducing agents.

CuO + H₂ → Cu + H₂O

CuO + Na → Cu + Na₂O

iii) Hydrogen burns in oxygen to form its oxide. It burns with a pop sound.

2H₂ + O₂ → 2H₂O

Alkali metals also burn vigorously when heated in oxygen to form their respective oxides.

Lithium forms monoxide.

4Li + O₂ → 2Li₂O

iv) Hydrogen burns in oxygen to form its oxide. It burns with a pop sound.

2H₂ + O₂ → 2H₂O

Alkali metals also burn vigorously when heated in oxygen to form their respective oxides.

Lithium forms monoxide.

4Li + O₂ → 2Li₂O

1. Oxides of alkali metals are basic in nature, whereas the oxide of hydrogen H₂O is a neutral oxide.
2. Hydrogen atom has only one shell, but halogens have two or more shells.