The formula for the sulfite ion is SO32-.
The sulfite ion consists of one sulfur atom and three oxygen atoms. The sulfur atom is at the center, and it is covalently bonded to the three oxygen atoms. The ion carries a charge of -2, which accounts for the way it typically interacts in chemical reactions. This negative charge is due to the presence of two additional electrons that are not involved in bonding, making the sulfite ion a polyatomic ion.