The thermal stability of alkaline earth metal carbonates increases from Be to Ba. This is because

Options

A. Covalent nature decreases and lonic nature increases
B. Lattice energy increases
C. Electropositive nature decreases
D. None of these

Answer

To understand why the thermal stability of alkaline earth metal carbonates increases from beryllium (Be) to barium (Ba), we can break down the reasoning into several steps:

### Step-by-Step Solution:

1. **Identify the Group**:
- Alkaline earth metals are located in Group 2 of the periodic table, which includes Be, Mg, Ca, Sr, and Ba.

2. **Understand Thermal Stability**:
- Thermal stability refers to the ability of a compound to withstand heat without decomposing. For carbonates, this means resisting breakdown into metal oxides and carbon dioxide upon heating.

3. **Trend in Thermal Stability**:
- It is observed that the thermal stability of alkaline earth metal carbonates increases as we move down the group from Be to Ba.

4. **Ionic vs. Covalent Character**:
- The carbonates of alkaline earth metals can exhibit both ionic and covalent character. The more ionic a compound is, the more stable it tends to be at higher temperatures.

5. **Cation Size and Charge Density**:
- As we move down the group, the size of the cation increases (from Be²⁺ to Ba²⁺). Larger cations have lower charge density, which leads to a decrease in covalent character of the carbonates.

6. **Fajans' Rule**:
- According to Fajans' rule, smaller cations have a higher tendency to polarize the anion (CO₃²⁻), leading to more covalent character. As the cation size increases down the group, the polarization effect decreases, resulting in more ionic character.

7. **Consequences of Increased Ionic Character**:
- With increased ionic character, the lattice energy of the carbonates increases. Higher lattice energy means that more energy is required to break the bonds in the compound, leading to greater thermal stability.

8. **Conclusion**:
- Therefore, the thermal stability of alkaline earth metal carbonates increases from Be to Ba because the covalent character decreases and the ionic character increases, making the compounds more stable at elevated temperatures.

### Final Answer:
The thermal stability of alkaline earth metal carbonates increases from Be to Ba because the covalent character of the carbonates decreases while the ionic character increases as we move down the group.