The shape of phosphorus trichloride is

Options

A. tetrahedral
B. pyramidal
C. trigonal pyramidal
D. linear

Answer

To determine the shape of phosphorus trichloride (PCl3), we can follow these steps:

### Step 1: Identify the central atom and its valence electrons
- The central atom in PCl3 is phosphorus (P).
- Phosphorus is in Group 15 of the periodic table and has 5 valence electrons.

### Step 2: Identify the surrounding atoms and their valence electrons
- The surrounding atoms are chlorine (Cl).
- Chlorine is in Group 17 and has 7 valence electrons. Each chlorine atom will form one bond with phosphorus.

### Step 3: Determine the number of bonds formed
- Phosphorus forms three covalent bonds with three chlorine atoms. This means phosphorus will share one of its electrons with each chlorine atom.

### Step 4: Calculate the steric number
- The steric number is calculated as the sum of the number of bond pairs and lone pairs around the central atom.
- In PCl3, there are 3 bond pairs (from the three P-Cl bonds) and 1 lone pair (remaining electron on phosphorus).
- Therefore, the steric number = 3 (bond pairs) + 1 (lone pair) = 4.

### Step 5: Determine the electron geometry
- With a steric number of 4, the electron geometry is tetrahedral.

### Step 6: Determine the molecular shape
- Since there is one lone pair, the molecular shape will differ from the electron geometry.
- The presence of the lone pair causes the shape to be distorted from tetrahedral to trigonal pyramidal (or simply pyramidal).
- This is because the lone pair occupies more space and repels the bond pairs, pushing them closer together.

### Conclusion
- The shape of phosphorus trichloride (PCl3) is **pyramidal**.