Question

Li and Mg shows similar properties because of similar (1) electric charge (2) ionic radii (3) charge/atomic radius (4) charge/(ionic radius \({ }^{2}\)

Short answer

Option (3) charge/atomic radius.

Step-by-step solution

Understand the key concept

Li (Lithium) and Mg (Magnesium) are elements from Group 1 and Group 2 of the periodic table, respectively. They demonstrate similar chemical properties due to their similar charge-to-radius ratios.

Analyze the charges and radii

Lithium has an electric charge of +1 and Magnesium has an electric charge of +2. Their respective ionic radii need to be considered to determine the similarity.

Compare charge/atomic radius and charge/ionic radius squared

The ratio of charge to atomic/ionic radius significantly impacts the element's properties. Comparing options, the charge-to-radius ratio is a more relevant comparison than the charge-to-ionic radius squared.

Key concepts

periodic table

The periodic table is a tabular arrangement of elements divided into groups and periods based on their atomic numbers. It helps predict the properties of elements based on their positions.
Li and Mg are found in Groups 1 and 2, respectively. Li is an alkali metal, while Mg is an alkaline earth metal.
Despite belonging to different groups, they show some similar chemical properties due to their positions in adjacent periods. This similarity arises because:

• Both elements have low atomic numbers, which means fewer electron shells.
• They possess relatively small atomic sizes.
• They share similar trends in ionization energy and electronegativity.

charge-to-radius ratio

The charge-to-radius ratio is a crucial factor in understanding chemical properties. It is the ratio of the electric charge of an ion to its ionic radius. This ratio influences the behavior and reactivity of elements.
Here's why:

• A higher charge-to-radius ratio typically means a stronger attraction between the ion and electrons, leading to higher reactivity.
• Li and Mg both have relatively high charge-to-radius ratios for their respective groups, leading to some common properties.
• For Li, the charge is +1, and for Mg, it's +2. Despite the higher charge, Mg's larger ionic radius balances it out, making the properties more comparable to Li.

ionic radii

Ionic radius is the measure of an ion's size once it has lost or gained electrons to form an ion.
Here are some important aspects:

• Li forms a +1 ion by losing one electron, resulting in an ionic radius smaller than its atomic radius.
• Mg forms a +2 ion by losing two electrons, also reducing its size compared to the neutral atom.
• The smaller ionic radii of both elements cause them to exhibit stronger electrostatic interactions with anions, influencing their chemical behavior similarly.

In conclusion, the shorter ionic radii and the charge-to-radius ratio explain why Li and Mg show comparable chemical properties despite being in different groups.