1 What is the total number of valence electrons in the Lewis structure of PO(OH)3? electrons 2 Draw a Lewis structure for PO(OH)3.
1 What is the total number of valence electrons in the Lewis structure of PO(OH)3? electrons 2 Draw a Lewis structure for PO(OH)3.
The Correct Answer and Explanation is:
1. Total number of valence electrons in PO(OH)₃:
To calculate the total number of valence electrons in the molecule PO(OH)₃, we add the valence electrons of each atom:
- P (Phosphorus): 5 valence electrons
- O (Oxygen): 6 valence electrons × 4 = 24
- One double bonded to phosphorus
- Three in hydroxyl groups (OH)
- H (Hydrogen): 1 valence electron × 3 = 3
Total = 5 (P) + 24 (O) + 3 (H) = 32 valence electrons
✅ Answer: 32 valence electrons
2. Lewis Structure of PO(OH)₃
Here’s how the molecule is structured:
- The central atom is phosphorus (P).
- It forms:
- One double bond with an oxygen atom (P=O).
- Three single bonds to hydroxyl groups (OH), each consisting of an oxygen single-bonded to phosphorus and to a hydrogen atom.
Lewis Structure:
O
||
H–O–P–O–H
|
O–H
- Each oxygen atom (including the doubly bonded one) has lone pairs to complete its octet.
- Phosphorus ends up with five bonds (10 electrons), which is acceptable because it can expand its octet (period 3 element).
- Each hydrogen is bonded to one oxygen, satisfying the duet rule (2 electrons).
Explanation
The molecule phosphorous acid or PO(OH)₃ is an oxoacid of phosphorus. Understanding its Lewis structure begins with tallying the total valence electrons, which is the sum of electrons each atom brings based on its group in the periodic table: phosphorus (Group 15) contributes 5, each oxygen (Group 16) contributes 6, and hydrogen (Group 1) contributes 1. With one phosphorus, four oxygens, and three hydrogens, the molecule contains 32 valence electrons.
In the structure, phosphorus serves as the central atom. It forms one double bond with oxygen (P=O), creating a strong π-bond and stabilizing the central atom. Additionally, phosphorus forms three single bonds with hydroxyl groups (OH), where each oxygen is also bonded to a hydrogen. Each oxygen atom has lone pairs to fulfill the octet rule, while hydrogen is satisfied with a single bond (2 electrons). The central phosphorus, though surrounded by more than 8 electrons (10 total), is able to do so because it’s in the third period and can use d-orbitals to expand its valence shell.
This structure maintains stability: oxygen atoms obey the octet rule, hydrogen obeys the duet rule, and phosphorus follows an expanded octet configuration. The molecule is polar due to the asymmetric distribution of electrons and the presence of polar O–H and P=O bonds. Drawing Lewis structures like this helps visualize bonding, lone pairs, and the shape of the molecule, which is important for understanding its chemical reactivity and physical properties.
