cations form when the atoms lose an electron or more and have + valency , so the mass will decrease and the effect of the nuclei on the remaining electrons will be stronger so it attracts them stronger toward the center so the size will decrease .. while in the anions the number of electrons increase so the attraction caused by the nuclei is weaker so the size is larger ... . size of the cation of an element < size of the atom of that element < size of the anion of that element