- Group IV consists of two subgroups: group IVb, main group, and group IVa. Group IVa consists of titanium, zirconium, and hafnium which are generally classified as transition metals. The main group consists of carbonium, silicium, germanium, tin, and lead. The main valency of the elements is IV, and the members of the group show a variation from nonmetallic to metallic behaviour in moving down the group. The reactivity of the elements increases down the group from carbon to lead. All react with oxygen on heating.