Question

Which of the following has lowest thermal stability? (a) \(\mathrm{BeCO}_{3}\) (b) \(\mathrm{MgCO}_{3}\) (c) \(\mathrm{CaCO}_{3}\) (d) \(\mathrm{BaCO}_{3}\)

Short answer

The carbonate with the lowest thermal stability is \( \text{BeCO}_3 \).

Step-by-step solution

Understand the trend of thermal stability for carbonates

Thermal stability refers to the compound's resistance to decomposition when heated. The thermal stability of metal carbonates increases down the group in the periodic table. This trend is observed in Group 2 (the alkaline earth metals), where beryllium is at the top, followed by magnesium, calcium, and barium.

Identify the order of increasing thermal stability

The order of increasing thermal stability for the carbonates of Group 2 elements is such that \[ ext{BeCO}_3 < ext{MgCO}_3 < ext{CaCO}_3 < ext{BaCO}_3. \] This means that as you move from Be to Ba down the group, the carbonates become more thermally stable.

Determine the carbonate with the lowest thermal stability

Based on the trend identified in Step 2, \[ ext{BeCO}_3 \] has the lowest thermal stability among the given options (a) through (d), as it is at the top of the Group 2 elements, making it less stable compared to others when heated.

Key concepts

Group 2 elements

Group 2 elements are known as the alkaline earth metals. These elements are found in the second column of the periodic table. Included in this group are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Each of these metals has two electrons in their outermost shell. This attribute gives them similar properties and characterizes their group behavior.
The elements in Group 2 tend to form compounds by losing their outermost electrons, resulting in a +2 oxidation state. This +2 charge makes them quite reactive, although they are generally less reactive than the elements in Group 1 (alkali metals).
Some key points about Group 2 elements include:

• They have higher densities and melting points than alkali metals.
• They are good conductors of electricity.
• They are typically harder than alkali metals.

These properties are because of their stronger metallic bonding compared to Group 1 elements. Overall, the characteristics of Group 2 elements make them a distinctive class of metals with important industrial applications.

alkaline earth metals

The alkaline earth metals, the alternate name for Group 2 elements, are significant in industrial processes and nature. These metals form oxides and hydroxides that are basic, hence the name 'alkaline'. Alkaline earth metals play vital roles in various chemical reactions, often forming ionic compounds with nonmetals.
One well-known compound is calcium carbonate ( Calcium carbonate is widely present in nature, making up limestone, chalk, and marble.

• They form compounds that are crucial in construction and manufacturing, such as cement and plaster.
• These metals are also necessary for human biology, with calcium being a critical component in bone formation.

The solubility of the alkaline earth metal compounds varies. As you move down the group, carbonates and sulfates become less soluble, which is important in water treatment and environmental chemistry. For students, understanding the elemental nature and reactions of alkaline earth metals helps to grasp their importance in both natural and industrial contexts.

periodic table trends

Understanding periodic table trends is essential for predicting the behavior of elements and their compounds. Trends provide insights into properties such as atomic radius, ionization energy, and thermal stability.
In Group 2, one major trend is that thermal stability increases as you move down the group from beryllium to calcium to barium. This pattern is evident in the carbonates of these metals. Beryllium carbonate ( BeCO_3 ) is unstable and decomposes at lower temperatures compared to barium carbonate ( BaCO_3 ).
A key reason behind this trend is the polarizing power of the cations. Smaller cations like beryllium have higher polarizing power, leading to weaker anion bonds in their carbonates. Hence, they break down more easily with heat.
Keep in mind for Group 2:

• The size of the atoms increases as you go down the group.
• With increasing atomic size, the polarizing effect decreases, thus enhancing stability.
• This also results in different solubility patterns for different compounds in the group.

Following these trends helps not only in predicting chemical reactivity and stability but also underlines the nature of chemical bonding across different elements and compounds.