▁periodic ▁table ▁layout s , ▁this ▁relationship ▁is ▁illustrated ▁more ▁clearly . ▁For ▁instance , ▁z inc ▁and ▁cad m ium ▁are ▁similar ▁to ▁b ery l li um ▁and ▁mag nes ium ▁in ▁their ▁atomic ▁rad ii , ▁ion ic ▁rad ii , ▁electron eg ativ ities , ▁and ▁also ▁in ▁the ▁structure ▁of ▁their ▁binary ▁comp ounds ▁and ▁their ▁ability ▁to ▁form ▁complex ▁ ions ▁with ▁many ▁nit ro gen ▁and ▁o xygen ▁lig ands , ▁such ▁as ▁complex ▁hyd rides ▁and ▁am ines . ▁However , ▁b ery l li um ▁and ▁mag nes ium ▁are ▁small ▁atoms , ▁unlike ▁the ▁heav ier ▁al kal ine ▁earth ▁met als ▁and ▁like ▁the ▁group ▁ 1 2 ▁elements ▁( which ▁have ▁a ▁greater ▁nuclear ▁charge ▁but ▁the ▁same ▁number ▁of ▁val ence ▁electrons ), ▁and ▁the ▁periodic ▁tr ends ▁down ▁group ▁ 2 ▁from ▁b ery l li um ▁to ▁rad ium ▁( similar ▁to ▁that ▁of ▁the ▁alk ali ▁met als ) ▁are ▁not ▁as ▁smooth ▁when ▁going ▁down ▁from ▁b ery l li um ▁to ▁mer cur y ▁( which ▁is ▁more ▁similar ▁to ▁that ▁of ▁the ▁p - block ▁main ▁groups ) ▁due ▁to ▁the ▁d - block ▁and ▁l anth an ide ▁contra ctions . ▁It ▁is ▁also ▁the ▁d - block ▁and ▁l anth an ide ▁contra ctions ▁that ▁give ▁mer cur y ▁many ▁of ▁its ▁distinct ive ▁properties . ▁ ▁Comp ounds ▁ ▁All ▁three ▁metal ▁ ions ▁form ▁many ▁t etra hed ral ▁species