Why does the melting point increase from sodium to aluminium?

Answer 1

The cation becomes more positive from sodium to aluminium, so its attraction for the sea of electrons increases.

Answer 2

The melting point increases from sodium to aluminum because as you move across the Periodic Table from left to right, the atomic size decreases while the nuclear charge increases. This results in stronger metallic bonding, requiring more energy to overcome and leading to higher melting points. Additionally, aluminum forms metallic bonds that are stronger than those of sodium due to its higher charge and smaller size.