Complete the Lewis structure of phosphoric acid in which formal charges are closest to zero. Formal charges do not need to be added. What is the molecular geometry around the phosphorus atom in your structure? H3PO4 Choose one: A. trigonal planar B. tetrahedral C. trigonal bipyramidal D. trigonal pyramidal
The Correct Answer and Explanation is:
The correct answer is:
B. tetrahedral
Explanation:
Phosphoric acid (H₃PO₄) is a common acid with the molecular formula H₃PO₄. To complete its Lewis structure with formal charges closest to zero, follow these steps:
- Total Valence Electrons Calculation:
- Phosphorus (P) contributes 5 electrons
- Oxygen (O) contributes 6 electrons × 4 = 24 electrons
- Hydrogen (H) contributes 1 electron × 3 = 3 electrons
- Total = 5 + 24 + 3 = 32 electrons
- Structure Arrangement:
- Phosphorus (P) is the central atom.
- Three oxygen atoms are bonded to P, each with a hydrogen attached to form hydroxyl (–OH) groups.
- The fourth oxygen is double-bonded to phosphorus.
- Lewis Structure Description:
- The central phosphorus forms:
- A double bond with one oxygen (P=O)
- Single bonds with three oxygen atoms (each bonded to a hydrogen, making –OH groups)
- The central phosphorus forms:
- Formal Charges Consideration:
- The structure ensures formal charges are minimized, with all atoms achieving stable electron configurations.
- Oxygen atoms with –OH groups have two lone pairs each.
- The double-bonded oxygen has two lone pairs as well.
- Phosphorus ends up surrounded by four regions of electron density: one double bond and three single bonds.
- Molecular Geometry Around Phosphorus:
- Phosphorus has four electron domains (regions of electron density) around it.
- According to Valence Shell Electron Pair Repulsion (VSEPR) theory, four electron domains arrange in a tetrahedral geometry to minimize repulsion.
Thus, the correct geometry around phosphorus in H₃PO₄ is tetrahedral, making option B the correct answer.
