Number of chlorine atoms which form equatorial bonds in PCl5 molecule are _

Options

A. 1
B. 2
C. 3
D. 4

Answer

To determine the number of chlorine atoms that form equatorial bonds in the PCl5 molecule, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Molecular Formula**: The molecular formula of the compound is PCl5, which indicates that it contains one phosphorus (P) atom and five chlorine (Cl) atoms.

2. **Determine the Valence Electrons**: Phosphorus has 5 valence electrons, and each chlorine atom has 7 valence electrons. Since there are 5 chlorine atoms, the total number of valence electrons contributed by chlorine is 5 × 7 = 35. Thus, the total number of valence electrons in PCl5 is 5 (from P) + 35 (from Cl) = 40 valence electrons.

3. **Calculate the Steric Number**: The steric number is calculated as the number of sigma bonds plus the number of lone pairs on the central atom (phosphorus in this case). In PCl5, phosphorus forms 5 sigma bonds with the 5 chlorine atoms and has no lone pairs. Therefore, the steric number is 5.

4. **Determine the Hybridization**: The steric number of 5 corresponds to sp³d hybridization. This means that the phosphorus atom undergoes hybridization to form five equivalent hybrid orbitals.

5. **Identify the Molecular Geometry**: With a steric number of 5 and sp³d hybridization, the molecular geometry of PCl5 is trigonal bipyramidal. In this geometry, there are two types of positions for the chlorine atoms: axial and equatorial.

6. **Identify the Positions of Chlorine Atoms**: In a trigonal bipyramidal geometry, there are three equatorial positions and two axial positions. The equatorial positions are located in a plane around the central atom, while the axial positions are above and below this plane.

7. **Count the Equatorial Chlorine Atoms**: Since there are three equatorial positions in the trigonal bipyramidal structure, three chlorine atoms will occupy these positions.

### Final Answer:
The number of chlorine atoms that form equatorial bonds in the PCl5 molecule is **3**.