What is the Lewis structure for SO₄²⁻ and is it polar or nonpolar?

The Lewis structure for SO₄²⁻ (sulfate ion) can be drawn as follows:

1. Start by counting the total number of valence electrons. Sulfur (S) has 6 valence electrons, and each oxygen (O) has 6 valence electrons. Since there are 4 oxygen atoms and a 2- charge, the total number of valence electrons is 6 (S) + 4 × 6 (O) + 2 (charge) = 32 electrons.
2. Place the sulfur atom in the center and arrange the four oxygen atoms around it.
3. Form single bonds between sulfur and each oxygen atom. This uses 8 electrons (4 bonds × 2 electrons).
4. Distribute the remaining 24 electrons as lone pairs on the oxygen atoms. Each oxygen atom will have 3 lone pairs, using up all 24 electrons.
5. To satisfy the octet rule for sulfur, form double bonds by moving lone pairs from two oxygen atoms to form double bonds with sulfur. This results in two double bonds and two single bonds.

The molecular geometry of SO₄²⁻ is tetrahedral. This is because the sulfur atom is surrounded by four regions of electron density (the four oxygen atoms), which arrange themselves in a tetrahedral shape to minimize electron repulsion.

Regarding polarity, SO₄²⁻ is a nonpolar molecule. Although the S-O bonds are polar due to the difference in electronegativity between sulfur and oxygen, the symmetrical tetrahedral arrangement of the oxygen atoms around the sulfur atom cancels out the dipole moments, resulting in a nonpolar molecule.