Examine this Lewis structure for the phosphate ion, PO4³-. How many valence electrons are around the P atom in this structure? :0 :0 :0: Nine Four Eight Twelve None of the above
The Correct Answer and Explanation is :
To correctly answer this question, let’s first analyze the Lewis structure of the phosphate ion (PO₄³⁻).
Step 1: Determine the total number of valence electrons in PO₄³⁻
- Phosphorus (P) is in Group 15 of the periodic table, so it has 5 valence electrons.
- Oxygen (O) is in Group 16 of the periodic table, so each oxygen atom has 6 valence electrons. Since there are four oxygen atoms, the total from oxygen is ( 4 \times 6 = 24 ) valence electrons.
- The phosphate ion has a charge of (3-), which means there are 3 additional electrons to account for.
Total valence electrons:
[ 5 (\text{from P}) + 24 (\text{from O}) + 3 (\text{extra electrons from the charge}) = 32 \, \text{electrons} ]
Step 2: Distribution of electrons in the Lewis structure
- In the Lewis structure of PO₄³⁻, phosphorus is at the center, surrounded by four oxygen atoms.
- Each oxygen atom typically forms a single bond with phosphorus. Since there are four bonds, each bond uses two electrons. This accounts for 8 electrons.
- The remaining 24 electrons are placed as lone pairs on the oxygen atoms.
Step 3: Count the electrons around the phosphorus atom
- Phosphorus forms four single bonds with the oxygen atoms. Each bond contains 2 electrons, so phosphorus is surrounded by ( 4 \times 2 = 8 ) electrons from the bonds.
- There are no lone pairs on the phosphorus atom in this structure, as phosphorus has a sufficient number of electrons through bonding to achieve its octet.
Answer: The number of valence electrons around the phosphorus atom is eight. This corresponds to the correct answer: Eight.
In summary, the phosphorus atom in the phosphate ion is surrounded by 8 valence electrons, all coming from the four bonds with the oxygen atoms. The structure satisfies the octet rule for oxygen and allows phosphorus to expand its valence shell, which is typical for elements in period 3 and beyond, such as phosphorus.