How does S{{O}_{4}} have a charge of -2?

The sulfate ion (SO4^2-) carries a charge of -2 due to the distribution of electrons within its constituent atoms. Let's break down the electron configuration and bonding in sulfate to understand its charge.

Sulfur (S) has an atomic number of 16, indicating that it has 16 electrons. The electron configuration of sulfur is 1s2 2s2 2p6 3s2 3p4. In the outermost energy level, sulfur has six valence electrons (two in the 3s orbital and four in the 3p orbital).

To achieve a more stable electron configuration, sulfur tends to gain two additional electrons to fill its valence shell, achieving a stable noble gas configuration like argon (1s2 2s2 2p6 3s2 3p6). This allows sulfur to attain a more favorable energy state.

Oxygen (O), on the other hand, has an atomic number of 8 and an electron configuration of 1s2 2s2 2p4. Oxygen has six valence electrons in its outer shell. To achieve a stable configuration, oxygen typically gains two electrons to complete its valence shell and resemble the electron configuration of neon (1s2 2s2 2p6).

In the sulfate ion (SO4^2-), one sulfur atom forms covalent bonds with four oxygen atoms. The sulfur atom shares two electrons with each oxygen atom, resulting in a total of eight shared electrons. These shared electrons form four double bonds, where each oxygen atom shares two electrons with the sulfur atom.

In the Lewis structure representation, the sulfur atom is in the center, surrounded by the four oxygen atoms. Each oxygen atom is connected to the sulfur atom by a double bond, and each oxygen atom also has two lone pairs of electrons.

Due to the electronegativity difference between sulfur and oxygen, the shared electrons are pulled closer to the oxygen atoms, resulting in a slightly negative charge on the oxygen atoms and a slightly positive charge on the sulfur atom.

Since each oxygen atom has a charge of -2 (due to gaining two electrons) and there are four oxygen atoms in the sulfate ion, the total negative charge from the oxygen atoms is -8. To balance this negative charge, the sulfur atom must have a charge of +6.

Therefore, the sulfate ion (SO4^2-) has a charge of -2, as the overall charge of the ion must be neutral. The -2 charge is the result of the sulfur atom (+6 charge) and the four oxygen atoms (-8 charge in total) combining to achieve electrical neutrality.