Question

The hydration energies of Group 2 ions are four to five times greater than that of the group 1 ions. This is due to their (1) smallcr size and increascd nuclear charge (2) greater size and decreased nuclear charge (3) smaller size and decreased nuclear charge (4) grcater size and increased nuclear charge

Short answer

The correct answer is (1) smaller size and increased nuclear charge.

Step-by-step solution

Identify the given data

The problem states that the hydration energies of Group 2 ions are four to five times greater than those of Group 1 ions.

Understand Hydration Energy

Hydration energy refers to the energy released when ions are surrounded by water molecules. It is generally higher for ions that are smaller and have a higher charge density.

Compare group trends

Group 2 ions (e.g., Mg²⁺, Ca²⁺) are smaller in size and have a higher nuclear charge compared to Group 1 ions (e.g., Na⁺, K⁺). This means Group 2 ions have a higher charge density.

Determine the correct reasoning

Smaller ions with greater nuclear charge will have stronger interactions with water molecules, thereby having higher hydration energies. Hence, the correct reason is: (1) smaller size and increased nuclear charge.

Key concepts

hydration energy

Hydration energy is the energy released when ions interact with water molecules. When an ion is hydrated, it forms a complex with water molecules, leading to a stable configuration.
This process releases energy, known as hydration energy.
The more negative this energy, the more stable the ion-water complex is.
Ions with higher hydration energy form stronger bonds with water molecules.
Factors influencing hydration energy include ion size and charge density.
Smaller ions with high charge densities tend to release more energy upon hydration.

ion charge density

Ion charge density relates to the charge of an ion relative to its size. The formula for charge density is: \[ \text{Charge Density} = \frac{\text{Charge}}{\text{Volume}} \] Smaller ions with higher charges have greater charge densities.
These ions attract water molecules more strongly.
High charge density enhances interactions with water, increasing hydration energy.
Hence, Group 2 ions, being doubly charged and smaller, have higher charge densities compared to Group 1 ions.

group trends in the periodic table

In the periodic table, elements are organized into groups and periods.
Group 2 elements (alkaline earth metals) exhibit specific trends:

• They are smaller than their Group 1 counterparts.
• They have higher nuclear charges due to the additional proton.
• These factors contribute to their high charge density.
• Hydration energy is significantly higher for Group 2 ions.

Understanding these trends helps predict element behavior, such as ion formation and interaction with water.

comparison of Group 1 and Group 2 elements

Comparing Group 1 and Group 2 elements reveals key differences:

• Group 1 elements (alkali metals) have a single positive charge (e.g., Na⁺).
• Group 2 elements (alkaline earth metals) typically have a double positive charge (e.g., Mg²⁺).
• Group 2 ions are smaller due to the higher nuclear charge.
• This increases their charge density, leading to higher hydration energies.

In essence, Group 2 elements form more stable ion-water complexes than Group 1 elements, making their interactions with water much stronger.