Question

All the elements of group 2 react with water to form metal hydroxide and hydrogen, except the element

• A. Barium
• B. Calcium
• C. Magnesium
• D. Beryllium

Hint:

Beryllium frequently exhibits anomalous behavior compared to the rest of the Group 2 elements due to its exceptionally small ionic size and high charge density. Whenever a question asks about a Group 2 element failing to show a typical metallic or ionic reaction trend, Beryllium is your primary candidate!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to identify which Group 2 alkaline earth metal does not react with water to form a hydroxide and hydrogen gas.

Step 2: Key Formula or Approach:
The general reaction of Group 2 metals (M) with water follows the chemical equation: $$\text{M} + 2\text{H}_2\text{O} \rightarrow \text{M(OH)}_2 + \text{H}_2\uparrow$$ The reactivity of these metals with water depends on their ionization enthalpies and hydration energies, both of which follow clear periodic trends as you move down the column.

Step 3: Detailed Explanation:
Let's evaluate the reactivity profile of Group 2 elements with water from top to bottom: 1.

Beryllium (Be): Beryllium has an exceptionally small atomic size, a very high ionization enthalpy, and a strong protective oxide film (BeO) on its surface. Because of these factors, beryllium is chemically inert toward water and does not react with liquid water or even red-hot steam.
2.

Magnesium (Mg): Does not react with cold water, but it reacts slowly with hot water and vigorously with steam to form magnesium hydroxide/oxide and hydrogen.
3.

Calcium (Ca), Strontium (Sr), and Barium (Ba): These elements have low ionization enthalpies and react readily and with increasing vigor with cold water to release hydrogen gas.
Therefore, Beryllium stands out as the unique exception that does not react with water.

Step 4: Final Answer:
The element that does not react with water is Beryllium, which corresponds to option (D).