Question

Property of alkaline earth metals that increases with their atomic number is: (a) Ionization energy (b) Solubility of their hydroxides (c) Solubility of their sulphates (d) Electronegativity

Short answer

The property that increases with atomic number is the solubility of their hydroxides (b).

Step-by-step solution

Understand Alkaline Earth Metals

Alkaline earth metals belong to group 2 of the periodic table. They include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements exhibit specific trends in their properties as their atomic numbers increase.

Recall Trends of Ionization Energy

Ionization energy generally decreases as you move down a group in the periodic table. For alkaline earth metals, the ionization energy decreases from beryllium to radium, meaning ionization energy does not increase with atomic number.

Analyze the Solubility of Hydroxides

The solubility of the hydroxides of alkaline earth metals increases as you move down the group. As the atomic number increases from Be to Ba, the solubility of their hydroxides in water increases.

Investigate the Solubility of Sulphates

In contrast to hydroxides, the solubility of sulphates of alkaline earth metals decreases with increasing atomic number. For example, BaSO₄ is sparingly soluble compared to BeSO₄.

Review Electronegativity Trends

Electronegativity generally decreases as you move down a group. For alkaline earth metals, electronegativity decreases with increasing atomic number. Therefore, electronegativity does not increase with atomic number.

Conclusion

Among the options, only the solubility of hydroxides consistently increases with the atomic number of alkaline earth metals. Therefore, option (b) is the correct answer.

Key concepts

Ionization Energy

Ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion. It essentially measures how strongly an atom holds on to its electrons. For alkaline earth metals, which are in group 2 of the periodic table, the ionization energy decreases as you progress down the group.
The main reason for this trend is the increasing atomic radius as you move down the group. With more electron shells, the outermost electrons are further from the nucleus. This makes it easier for those electrons to be removed.

• Beryllium (Be) at the top has the highest ionization energy among the alkaline earth metals.
• Radium (Ra) at the bottom has the lowest ionization energy in this group.

So, as atomic number increases for alkaline earth metals, the ionization energy decreases, opposite to what might increase with atomic number.

Solubility Trends

Solubility refers to the ability for a substance to dissolve in a solvent. For alkaline earth metals, solubility shows various trends depending on the compound type, such as hydroxides or sulfates.
Understanding these trends is crucial for predicting how these substances will behave in different environments, like in natural waters or industrial processes.

• Hydroxides of these metals become more soluble as you move down the group.
• Sulphates show a trend of decreasing solubility down the group.

These trends are essential in various applications, including environmental science and industries.

Periodic Table Groups

Periodic table groups are vertical columns in the periodic table where elements share similar properties due to having the same number of electrons in their outer shell. Group 2, where alkaline earth metals reside, is an excellent example of such a group.
Characteristics shared by these elements include:

• Having two valence electrons.
• Being shiny and somewhat reactive, though more so than noble gases.
• Forming ionic compounds by losing their two outer electrons.

Understanding these periodic trends helps in predicting and explaining the chemical behavior of these elements.

Electronegativity

Electronegativity measures an atom's ability to attract and bond with electrons. In the context of alkaline earth metals, electronegativity tends to decrease as you move down the group.
This trend is attributed to the larger atomic size and the greater shielding effect as you move down the group, making it harder for the nucleus to attract electrons.

• Beryllium (Be) has a higher electronegativity compared to, say, Barium (Ba).
• These decreasing trends can impact the type of compounds they form and their reactivity.

Understanding electronegativity and its trends allows chemists to predict reactivity and bonding potential in these metals.

Solubility of Hydroxides

For alkaline earth metals, the solubility of their hydroxides in water increases as you move down the group. This means hydroxides of elements like barium are more soluble than those of magnesium.

• This trend occurs because as the metals get heavier, their metal hydroxide solubility increases.
• It’s crucial in applications like soil chemistry and water treatment where solubility will dictate reactions taking place.

In practice, this trend simplifies predictions of how such hydroxides will dissolve and interact in various chemical environments. As the atomic number increases, this property strengthens among the group.

Solubility of Sulphates

In contrast to hydroxides, the solubility of sulphates for alkaline earth metals decreases down the group.
Barium sulfate (BaSO₄), for example, is much less soluble than magnesium sulfate (MgSO₄).

• This inverse relationship is due to the increasing lattice energy overcoming the hydration energy as atomic number increases.
• BaSO₄’s low solubility is a reason for its use in medical imaging as a contrast agent and in industries where low solubility expands its utility.

Hence, understanding solubility trends of sulphates helps predict the behavior and applicability of these compounds in various environments.