Silicon (Si) has been closely tied to human civilization. Clay and cement both contain it: clay is fired into pottery and bricks, cement is made into concrete, and in recent decades silicon's semiconductor behavior has driven electronics forward.

Basic data

Note: the earlier version of this article gave the atomic weight as 28.8055, which does not match the accepted value of about 28.09; it has been corrected here.

Electron configuration

Silicon sits in period 3, group 14, and has 14 electrons. They fill in order of increasing energy: two in the 1s orbital of the K shell, eight in the 2s and 2p orbitals of the L shell, two in the 3s orbital of the M shell, and the last two in 3p, giving 1s²2s²2p⁶3s²3p². The four valence electrons explain why silicon forms four covalent bonds, which underlies its behavior as a semiconductor and the backbone of silicone polymers.