What is the molecular geometry of the sulfate ion, SO_4^{2-}?

• A. Tetrahedral
• B. Trigonal pyramidal
• C. Trigonal planar
• D. Square planar

Answer: (A)

Verified step by step guidance

1. Determine the Lewis structure of the sulfate ion, SO_4^{2-}. Start by counting the total number of valence electrons: sulfur has 6 valence electrons, each oxygen has 6, and add 2 extra electrons for the 2- charge.
2. Draw the skeletal structure with sulfur as the central atom bonded to four oxygen atoms. Connect sulfur to each oxygen with single bonds initially.
3. Distribute the remaining electrons to complete the octets of the oxygen atoms, then check if sulfur can expand its octet by forming double bonds if necessary to minimize formal charges.
4. Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to determine the molecular geometry. Count the regions of electron density (bonding pairs and lone pairs) around the central sulfur atom.
5. Since there are four bonding pairs and no lone pairs on sulfur, the electron pairs arrange themselves to minimize repulsion in a tetrahedral shape, giving the sulfate ion a tetrahedral molecular geometry.