pa ired ▁electrons ; ▁thus , ▁making ▁the ▁species ▁very ▁re active . ▁Z inc ( I ) ▁is ▁known ▁mostly ▁in ▁the ▁gas ▁phase , ▁in ▁such ▁comp ounds ▁as ▁linear ▁Z n 2 Cl 2 , ▁analog ous ▁to ▁cal om el . ▁ ▁In ▁the ▁solid ▁phase , ▁the ▁rather ▁ex otic ▁comp ound ▁dec am eth y ld iz inc oc ene ▁( C p * Z n – Z n C p *) ▁is ▁known . ▁ ▁Classification ▁The ▁elements ▁in ▁group ▁ 1 2 ▁are ▁usually ▁considered ▁to ▁be ▁d - block ▁elements , ▁but ▁not ▁transition ▁elements ▁as ▁the ▁d - shell ▁is ▁full . ▁Some ▁authors ▁class ify ▁these ▁elements ▁as ▁main - group ▁elements ▁because ▁the ▁val ence ▁electrons ▁are ▁in ▁ns 2 ▁orbit als . ▁Nevertheless , ▁they ▁share ▁many ▁characteristics ▁with ▁the ▁neighbor ing ▁group ▁ 1 1 ▁elements ▁on ▁the ▁periodic ▁table , ▁which ▁are ▁almost ▁univers ally ▁considered ▁to ▁be ▁transition ▁elements . ▁For ▁example , ▁z inc ▁shares ▁many ▁characteristics ▁with ▁the ▁neighbor ing ▁transition ▁metal , ▁co pper . ▁Z inc ▁complex es ▁mer it ▁inclusion ▁in ▁the ▁Ir ving - Will iams ▁series ▁as ▁z inc ▁forms ▁many ▁complex es ▁with ▁the ▁same ▁sto ichi ometry ▁as ▁complex es ▁of ▁co pper ( II ), ▁al beit ▁with ▁smaller ▁stability ▁constants . ▁There ▁is ▁little ▁similarity ▁between ▁cad m ium ▁and ▁silver ▁as ▁comp ounds ▁of ▁silver ( II ) ▁are ▁rare ▁and ▁those ▁that ▁do ▁exist