Why does copper have a higher melting point than aluminium? Why does the melting point increase as you go down groups anyway? Aluminium has higher charge (+3) and a smaller radius, meaning that there is a higher charge density and thus stronger forces of attraction to the lattice. While copper has a charge of +1 and a bigger radius. However, Copper has a higher number of protons, or a stronger positive charge in the nucleus, is this the reason ?