Atoms of the metals form cations after losing one or more electrons. When a neutral metal atom will lose electrons, the number of electrons will be less than the protons. As a result, forces of attraction will increase between the positively charged nucleus and electrons and the cloud of electrons will contract. This results in the smaller size of cation than the corresponding atom. Also, when the cation is formed by losim electrons of the outermost shell, it has one shell less than the atom and so its size is smaller.
