<Tr> <Th> Element category </Th> <Td> post-transition metal </Td> </Tr> <Tr> <Th> Block </Th> <Td> p - block </Td> </Tr> <Tr> <Th> Electron configuration </Th> <Td> (Xe) 4f 5d 6s 6p </Td> </Tr> <Tr> <Th> Electrons per shell </Th> <Td> 2, 8, 18, 32, 18, 4 </Td> </Tr>

Five of the principal sources of lead contamination that were present in the mid-20th century