Beryllium and Aluminium have similar properties because they

Analysis of the Question

The question asks for the reason behind the chemical similarities between Beryllium (Be) and Aluminium (Al). This is a classic topic in Periodic Table trends known as the "Diagonal Relationship."

Concept Explanation: The Diagonal Relationship

In the Periodic Table, certain elements in the second period show a striking similarity to the elements located diagonally below them in the third period. This happens because of a balance between two factors:

1. Atomic/Ionic Size: As you move across a period, size decreases. As you move down a group, size increases. These two opposing trends result in Beryllium and Aluminium having similar ionic radii.
2. Charge-to-Size Ratio (Ionic Potential): Because their sizes are similar and their charges are comparable, they exert a similar polarizing power on anions. This leads to them forming compounds with similar covalent character and acidic/amphoteric properties.

Specifically:

• Beryllium (Group 2, Period 2) is diagonally related to Aluminium (Group 13, Period 3).
• Lithium (Group 1, Period 2) is diagonally related to Magnesium (Group 2, Period 3).
• Boron (Group 13, Period 2) is diagonally related to Silicon (Group 14, Period 3).

Step-by-Step Solution

1. Evaluate Option A: While both are metals, many other metals (like Sodium and Calcium) are not similar to each other. Being a metal is not the specific reason for their unique chemical resemblance.
2. Evaluate Option B: Beryllium is in Group 2, and Aluminium is in Group 13. They do not belong to the same group.
3. Evaluate Option C: Beryllium is in Period 2, and Aluminium is in Period 3. They do not belong to the same period.
4. Evaluate Option D: Beryllium (atomic number 4) is located at the top-left of the p-block area, and Aluminium (atomic number 13) is located diagonally to its bottom-right. This diagonal placement is the standard chemical explanation for their shared properties, such as their oxides being amphoteric.

Conclusion

The similarity in the properties of Beryllium and Aluminium is a direct result of their diagonal positioning in the Periodic Table, which balances their ionic charges and sizes.

Exam Tip

To remember diagonal relationships, just think of the "staircase" pattern starting from Lithium. Remember the mnemonic: Li-Mg, Be-Al, B-Si. These pairs are famous in JAMB Chemistry for having similar chemical behaviors, such as forming covalent bonds and having amphoteric oxides!