Learn: Thermal Stability of Carbonates and Nitrates

Welcome!Building on what you've already learned about Group 2 trends in reactivity, solubility, and bonding, we're now exploring thermal stability of carbonates and nitrates. This lesson will explain the trends and their reasons, helping you understand why these compounds behave differently as you move down the group.

What is thermal stability?Thermal stability refers to how easily a substance decomposes when heated. For Group 2 carbonates and nitrates, this means breaking down into simpler products like oxides and gases. This property depends on the charge density of the metal ion.

Charge density of Group 2 ionsCharge density is the ratio of charge to size for an ion. Smaller ions with higher charge (e.g., Mg2+) have higher charge density, which strongly polarises nearby molecules or ions. Larger ions, like Ba2+, have lower charge density and less polarising power.

Thermal stability of carbonatesGroup 2 carbonates decompose upon heating to form the metal oxide and carbon dioxide. For example: CaCO3 → CaO + CO2. As you move down the group, thermal stability increases because larger ions (e.g., Ba2+) have lower charge density and less polarising power, making the carbonate ion more stable.

Thermal stability of nitratesGroup 2 nitrates decompose to form the metal oxide, nitrogen dioxide, and oxygen. For example: 2Ca(NO3)2 → 2CaO + 4NO2 + O2. Similar to carbonates, thermal stability increases down the group because larger ions polarise the nitrate ion less, stabilising it against decomposition.

Group 2 trends in thermal stabilityAs you move down Group 2, carbonates and nitrates become more thermally stable. This is due to the decreasing charge density of the metal ions (e.g., Mg2+ → Ba2+). Lower charge density ions polarise the carbonate or nitrate less, stabilising the compound.

Review Time!Great work! You've learned about the thermal stability trends of Group 2 carbonates and nitrates. Let's test your understanding with a few final questions.