The atomic number of an element is 17. The number of orbitals containing electron pairs in its valence shell is

Options

A. Eight
B. Six
C. Three
D. Two

Explanation

To solve the problem, we need to determine the number of orbitals containing electron pairs in the valence shell of an element with an atomic number of 17.

### Step-by-Step Solution:

1. **Identify the Element**:
The atomic number 17 corresponds to the element Chlorine (Cl).

2. **Determine the Electronic Configuration**:
The electronic configuration of Chlorine can be determined by filling the orbitals according to the Aufbau principle:
- 1s² (2 electrons)
- 2s² (2 electrons)
- 2p⁶ (6 electrons)
- 3s² (2 electrons)
- 3p⁵ (5 electrons)

Therefore, the complete electronic configuration of Chlorine is:
\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \]

3. **Identify the Valence Shell**:
The valence shell is the outermost shell where the valence electrons are located. For Chlorine, the valence shell is the third shell (n=3), which includes:
- 3s² (2 electrons)
- 3p⁵ (5 electrons)

4. **Count the Orbitals in the Valence Shell**:
In the valence shell (n=3):
- The 3s subshell has 1 orbital.
- The 3p subshell has 3 orbitals.

Therefore, the total number of orbitals in the valence shell is:
\[ 1 \, (from \, 3s) + 3 \, (from \, 3p) = 4 \, \text{orbitals} \]

5. **Determine the Orbitals with Electron Pairs**:
- The 3s orbital contains 2 electrons, which form 1 pair.
- The 3p subshell has 5 electrons. According to Hund's rule, these electrons will occupy the three 3p orbitals singly before pairing occurs. Thus, there will be no pairs in the 3p orbitals.

Therefore, the only orbital containing an electron pair is the 3s orbital.

6. **Final Count**:
The number of orbitals containing electron pairs in the valence shell of Chlorine is:
\[ 1 \, (from \, 3s) \]

### Conclusion:
The number of orbitals containing electron pairs in the valence shell of the element with atomic number 17 (Chlorine) is **1**.

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