In a transition series, as the atomic number increases, paramagnetism

Options

A. increase gradually
B. decrease gradually
C. first increase to a maximum and then decrease
D. first decrease to a minimum and then increase

Answer

To solve the question regarding the behavior of paramagnetism in a transition series as the atomic number increases, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Paramagnetism**:
- Paramagnetism is a property of materials that are attracted to magnetic fields due to the presence of unpaired electrons in their atomic or molecular orbitals. The more unpaired electrons there are, the stronger the paramagnetic behavior.

2. **Identify the Transition Series**:
- Focus on the 3d transition series: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn).

3. **Determine Electron Configurations**:
- Write the electron configurations for the 3d transition metals:
- Sc: [Ar] 4s² 3d¹
- Ti: [Ar] 4s² 3d²
- V: [Ar] 4s² 3d³
- Cr: [Ar] 4s¹ 3d⁵ (exception)
- Mn: [Ar] 4s² 3d⁵
- Fe: [Ar] 4s² 3d⁶
- Co: [Ar] 4s² 3d⁷
- Ni: [Ar] 4s² 3d⁸
- Cu: [Ar] 4s¹ 3d¹⁰ (exception)
- Zn: [Ar] 4s² 3d¹⁰

4. **Count Unpaired Electrons**:
- Count the number of unpaired electrons for each element:
- Sc: 1 unpaired electron
- Ti: 2 unpaired electrons
- V: 3 unpaired electrons
- Cr: 6 unpaired electrons (due to half-filled d-orbital stability)
- Mn: 5 unpaired electrons
- Fe: 4 unpaired electrons
- Co: 3 unpaired electrons
- Ni: 2 unpaired electrons
- Cu: 1 unpaired electron
- Zn: 0 unpaired electrons

5. **Analyze the Trend**:
- Observe the trend in the number of unpaired electrons as you move from Sc to Zn:
- The number of unpaired electrons increases from Sc (1) to Cr (6), then decreases from Mn (5) to Zn (0).
- This indicates that paramagnetism first increases, reaches a maximum at Cr, and then decreases.

6. **Conclusion**:
- Based on the analysis, we conclude that in a transition series, as the atomic number increases, paramagnetism first increases to a maximum and then decreases. Therefore, the correct answer is: **first increases to a maximum and then decreases**.