▁a ▁transition ▁metal . ▁ ▁Rel ations hip ▁with ▁the ▁al kal ine ▁earth ▁met als ▁Although ▁group ▁ 1 2 ▁lies ▁in ▁the ▁d - block ▁of ▁the ▁modern ▁ 1 8 - column ▁periodic ▁table , ▁the ▁d ▁electrons ▁of ▁z inc , ▁cad m ium , ▁and ▁( al most ▁always ) ▁mer cur y ▁behave ▁as ▁core ▁electrons ▁and ▁do ▁not ▁take ▁part ▁in ▁bond ing . ▁This ▁behavior ▁is ▁similar ▁to ▁that ▁of ▁the ▁main - group ▁elements , ▁but ▁is ▁in ▁stark ▁contrast ▁to ▁that ▁of ▁the ▁neighbor ing ▁group ▁ 1 1 ▁elements ▁( co pper , ▁silver , ▁and ▁gold ), ▁which ▁also ▁have ▁filled ▁d - sub sh ells ▁in ▁their ▁ground - state ▁electron ▁configuration ▁but ▁behave ▁chem ically ▁as ▁transition ▁met als . ▁For ▁example , ▁the ▁bond ing ▁in ▁chrom ium ( II ) ▁sul f ide ▁( Cr S ) ▁involves ▁mainly ▁the ▁ 3 d ▁electrons ; ▁that ▁in ▁iron ( II ) ▁sul f ide ▁( Fe S ) ▁involves ▁both ▁the ▁ 3 d ▁and ▁ 4 s ▁electrons ; ▁but ▁that ▁of ▁z inc ▁sul f ide ▁( Z n S ) ▁involves ▁only ▁the ▁ 4 s ▁electrons ▁and ▁the ▁ 3 d ▁electrons ▁behave ▁as ▁core ▁electrons . ▁Indeed , ▁useful ▁comparison ▁can ▁be ▁made ▁between ▁their ▁properties ▁and ▁the ▁first ▁two ▁members ▁of ▁group ▁ 2 , ▁b ery l li um ▁and ▁mag nes ium , ▁and ▁in ▁earlier ▁short - form