Question

Elements of II A group having electronic configuration \(\mathrm{ns}^{2}\) are called alkaline earth metals because (1) they occur in earth and their oxides are strongly alkaline (2) their salts form only alkaline solution (3) they all form divalent cations only (4) their oxides are weakly basic

Short answer

Option (1): They occur in earth and their oxides are strongly alkaline.

Step-by-step solution

Understand the Electronic Configuration

Elements of Group IIA (or Group 2) have an electronic configuration of \(\text{ns}^2\). This includes elements such as Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).

Identify Characteristics of Alkaline Earth Metals

Alkaline earth metals typically form oxides that are strongly basic in nature. This means their oxides can react with water to form hydroxides, which are alkaline.

Evaluate the Options

Examine the options given:1. They occur in earth and their oxides are strongly alkaline2. Their salts form only alkaline solution3. They all form divalent cations only4. Their oxides are weakly basicThe correct answer describes not only their occurrence and properties but also the nature of their oxides.

Determine the Correct Answer

Option (1) states that they occur in earth and their oxides are strongly alkaline. This correctly identifies the nature of alkaline earth metals.

Key concepts

electronic configuration

The electronic configuration of elements provides a way to understand the arrangement of electrons in an atom. For Group IIA elements, also known as alkaline earth metals, the electronic configuration is represented as \( \text{ns}^{2} \). This means they have two electrons in their outermost s-orbital. This configuration is crucial because it governs the chemical properties of these elements.
For example: Beryllium (Be) has the configuration \( 1s^{2}2s^{2} \), while Magnesium (Mg) is \( 1s^{2}2s^{2}2p^{6}3s^{2} \). The presence of these two electrons in the outermost shell makes them highly reactive but less so than the alkali metals of Group I.
Knowing the electronic configuration helps you predict the chemical behavior and reactivity, explaining why these elements form divalent cations (ions with a +2 charge).

Group IIA

Group IIA of the periodic table consists of alkaline earth metals. These metals are located in the second column of the periodic table. The members of this group include:

• Beryllium (Be)
• Magnesium (Mg)
• Calcium (Ca)
• Strontium (Sr)
• Barium (Ba)
• Radium (Ra)

Alkaline earth metals are known for their shiny, silvery-white appearance and are somewhat reactive under standard conditions. Because these elements reside in Group IIA, they share common properties like the formation of basic oxides and divalent cations. They play a vital role in various biological and industrial applications.
For instance, calcium is fundamental in biological processes such as muscle contraction and bone structure.

basic oxides

The oxides of alkaline earth metals are known as basic oxides. These oxides can react with water to form hydroxides, which are strongly basic in nature. This means they can neutralize acids.
For example:

• Magnesium oxide (MgO) reacts with water to form magnesium hydroxide \( \text{MgO} + \text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 \).
• Calcium oxide (CaO), commonly known as quicklime, reacts with water to produce calcium hydroxide \( \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \), which is used to improve soil pH and in the process of making cement.

These basic oxides have high melting points and typically exhibit high thermal stability. Their ability to form hydroxides is essential in many chemical reactions and industrial processes.

divalent cations

A divalent cation is an ion with a +2 charge. Alkaline earth metals commonly form divalent cations by losing their two outermost s-electrons. This leads to the \( \text{M}^{2+} \) ions, where M represents the metal.
In chemical terms, the process is as follows:
\[ \text{M} \rightarrow \text{M}^{2+} + 2e^{-} \]
The loss of two electrons results in a stable, positively charged ion. This stability makes them key participants in many chemical reactions.
For example, Calcium (Ca) readily forms \( \text{Ca}^{2+} \) ions that are essential for biological functions like cellular signaling, muscle contraction, and bone formation. Similarly, \( \text{Mg}^{2+} \) ions are crucial in photosynthesis and enzyme function.
The consistent formation of divalent cations is a fundamental characteristic of Group IIA elements, impacting their chemical behavior and interactions.