Reactions of Hydrogen

Hydrogen's low ionization energy makes it act like an alkali metal:

However, it half-filled valence shell (with a 1s¹ configuration) with one e− also causes hydrogen to act like a halogen non-metal to gain noble gas configuration by adding an additional electron

with M representing Group 1 Alkali metals  

Examples:

2K(s)+H₂(g)→2KH(s)

2K(s)+Cl₂(g)→2KCl(s)

 with M representing Group 2 Alkaline Earth metals  

Example:

Ca(s)+H₂(g)→CaH₂(s)

Ca(s)+Cl₂(g)→CaCl₂(s)