- al umin ium ▁am alg am ▁when ▁the ▁two ▁pure ▁met als ▁come ▁into ▁contact . ▁Since ▁the ▁am alg am ▁react s ▁with ▁air ▁to ▁give ▁al umin ium ▁ox ide , ▁small ▁amounts ▁of ▁mer cur y ▁cor ro de ▁al umin ium . ▁For ▁this ▁reason , ▁mer cur y ▁is ▁not ▁allowed ▁ab o ard ▁an ▁aircraft ▁under ▁most ▁circumstances ▁because ▁of ▁the ▁risk ▁of ▁it ▁forming ▁an ▁am alg am ▁with ▁exposed ▁al umin ium ▁parts ▁in ▁the ▁aircraft . ▁ ▁Chem istry ▁Most ▁of ▁the ▁chem istry ▁has ▁been ▁observed ▁only ▁for ▁the ▁first ▁three ▁members ▁of ▁the ▁group ▁ 1 2 . ▁The ▁chem istry ▁of ▁cop ern ici um ▁is ▁not ▁well ▁established ▁and ▁therefore ▁the ▁rest ▁of ▁the ▁section ▁de als ▁only ▁with ▁z inc , ▁cad m ium ▁and ▁mer cur y . ▁ ▁Period ic ▁tr ends ▁All ▁elements ▁in ▁this ▁group ▁are ▁met als . ▁The ▁similarity ▁of ▁the ▁met all ic ▁rad ii ▁of ▁cad m ium ▁and ▁mer cur y ▁is ▁an ▁effect ▁of ▁the ▁l anth an ide ▁contra ction . ▁So , ▁the ▁tr end ▁in ▁this ▁group ▁is ▁unlike ▁the ▁tr end ▁in ▁group ▁ 2 , ▁the ▁al kal ine ▁earth s , ▁where ▁met all ic ▁radius ▁increases ▁smooth ly ▁from ▁top ▁to ▁bottom ▁of ▁the ▁group . ▁All ▁three ▁met als ▁have ▁relatively ▁low ▁mel ting ▁and ▁bo iling ▁points , ▁indicating ▁that ▁the ▁met all ic ▁bond ▁is ▁relatively ▁weak ,