The alkaline earth metals have smaller size than those of corresponding alkali metals, this is due to

Options

A. increase in ionisation enthalpy
B. decrease in nuclear charge
C. increase in nuclear charge
D. increase in number of shells

Answer

To understand why alkaline earth metals have a smaller size than their corresponding alkali metals, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Identify the Groups**:
- Alkali metals belong to Group 1 of the periodic table, while alkaline earth metals belong to Group 2.

2. **Electron Configuration**:
- Alkali metals have one electron in their outermost shell (ns¹), whereas alkaline earth metals have two electrons in their outermost shell (ns²).

3. **Nuclear Charge**:
- As we move from Group 1 to Group 2, the number of protons in the nucleus increases. This increase in the number of protons leads to an increase in the nuclear charge.

4. **Effect of Nuclear Charge on Atomic Size**:
- The increased nuclear charge in alkaline earth metals results in a stronger attraction between the nucleus and the electrons. This stronger attraction pulls the electrons closer to the nucleus, leading to a decrease in atomic size.

5. **Comparison of Atomic Sizes**:
- Therefore, alkaline earth metals, with their higher nuclear charge compared to alkali metals, have a smaller atomic radius.

6. **Conclusion**:
- The reason for the smaller size of alkaline earth metals compared to alkali metals is the increase in nuclear charge as we move from Group 1 to Group 2.

### Final Answer:
The alkaline earth metals have smaller size than those of corresponding alkali metals due to the **increase in nuclear charge**.