The alkali metals are low melting . Which of the following alkali metal is expected to melt if the room temperature rises to 30∘C?
(a) Na (b) K (c) Rb (d) Cs
The energy binding th eatoms in the crysta lattice of the alkali metals is low due to their large atomic radii and especially due to the presence of one valence electron per metal atom as compared to large number available vacant orbitals.
Hence, alkali metals have low melting and boiling points. The melting point of alkali metls decreases from Li to Cs as cohesive force decreases with increases in atomic size.
Melting point of Cs = 302 K i.e. 29∘C.