A tetrahalide is a compound containing 4 halogen atoms (fluorine, chlorine, bromine, iodine, or astatine) in each of its molecules.
Silicon and lead
PbBr4 and PbI4 are unstable due to the high oxidation state of lead (Pb) in these compounds, which makes them prone to reduction. Lead typically exhibits stable oxidation states of +2 and +4, but in these tetrahalides, the +4 state is less stable due to the larger size and lower electronegativity of bromine and iodine, which can lead to bond weakening. Additionally, the formation of stable lower oxidation state compounds, such as PbBr2 or PbI2, is thermodynamically favored, contributing to the instability of PbBr4 and PbI4.