Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

Options

A. 15
B. 16
C. 9
D. 17

Answer

To find the atomic number of the element present in the third period and seventeenth group of the periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Period and Group**:
- The element is in the **third period** and the **seventeenth group** of the periodic table.

2. **Determine the Principal Quantum Number**:
- The period number corresponds to the principal quantum number (n) of the valence shell. For the third period, **n = 3**.

3. **Identify the Group Characteristics**:
- The elements in the seventeenth group are known as halogens. The outermost electronic configuration for halogens is typically represented as **ns² np⁵**.
- For the third period, this becomes **3s² 3p⁵**.

4. **Write the Complete Electronic Configuration**:
- The complete electronic configuration includes all the filled inner shells:
- For the first period: 1s²
- For the second period: 2s² 2p⁶
- For the third period: 3s² 3p⁵
- Therefore, the complete electronic configuration is:
- **1s² 2s² 2p⁶ 3s² 3p⁵**.

5. **Count the Total Number of Electrons**:
- The atomic number of an element is equal to the total number of electrons in a neutral atom.
- Count the electrons:
- 1s² = 2
- 2s² = 2
- 2p⁶ = 6
- 3s² = 2
- 3p⁵ = 5
- Total = 2 + 2 + 6 + 2 + 5 = **17**.

6. **Conclusion**:
- The atomic number of the element located in the third period and seventeenth group is **17**.

### Final Answer:
The atomic number of the element is **17**.

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