Accepted answer
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Problem
Determine the PCl₅ Lewis structure by following the systematic steps of valence electron counting, bond distribution, and VSEPR geometry analysis.
Step 1: Total Valence Electrons
Phosphorus (P) is in Group 15 and Chlorine (Cl) is in Group 17.
| Atom | Count | Valence Electrons | Subtotal |
|---|---|---|---|
| P | 1 | 5 | 5 |
| Cl | 5 | 7 | 35 |
| Total Sum | 40 | ||
Step 2 & 3: Skeleton and Octet Distribution
Connect the cental Phosphorus to five Chlorine atoms using single bonds (\(10\) electrons). Fill the octets of the Chlorine atoms with lone pairs (\(30\) electrons).
Step 4: The Lewis Structure (Expanded Octet)
Since Phosphorus is in the third period, it can accommodate an expanded octet. In PCl₅, it has 10 bonding electrons and zero lone pairs.
Step 5: Formal Charges
| Atom | Valence (V) | Lone (L) | Bond (B) | FC = V - L - B/2 |
|---|---|---|---|---|
| P | 5 | 0 | 10 | 5 - 0 - 5 = 0 |
| Cl | 7 | 6 | 2 | 7 - 6 - 1 = 0 |
Step 6: VSEPR Molecular Geometry
PCl₅ belongs to the AX₅ class. With 5 bonding pairs and 0 lone pairs, phosphorus adopts a Trigonal Bipyramidal geometry.
Summary
- Valence Electrons: 40
- Formal Charges: All atoms are zero
- Molecular Geometry: Trigonal Bipyramidal
- Bond Angles: \(90^\circ\) (axial-equatorial) and \(120^\circ\) (equatorial-equatorial)
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