All the elements in a group (family) have a common valency. For example, all the elements of the carbon family (carbon, silicon, germanium, tin and lead) have common valency four. However, some of these elements can also have valency two. Which of the following can have valency two?

Group 14 elements (Carbon family) have a general electronic configuration of ns²np², typically exhibiting a valency of four [t6]. However, as one moves down the group, the 'inert pair effect' becomes prominent. This effect occurs because the ns² electrons are more tightly held by the nucleus and become increasingly reluctant to participate in bonding [t1]. Consequently, heavier elements like germanium (Ge), tin (Sn), and lead (Pb) can exhibit a valency of two by losing or sharing only their two p-electrons [t1][t4]. While carbon and silicon primarily show a +4 oxidation state, germanium can form divalent compounds like germylenes [t3], and for tin and lead, the +2 state is common and stable [t2]. Specifically, the stability of the +2 oxidation state increases from Ge to Pb, making germanium, tin, and lead the members capable of exhibiting valency two [t1][t6].

Sources

1. [1] https://www.sciencedirect.com/science/article/abs/pii/S0010854503002352