Question

Lithium shows diagonal relationship with

• A. $\mathrm{Mg}$
• B. $\mathrm{Al}$
• C. $\mathrm{Be}$
• D. $\mathrm{Na}$

Hint:

Remember the three classic diagonal pairs of the periodic table: Lithium ($\mathrm{Li}$) with Magnesium ($\mathrm{Mg}$), Beryllium ($\mathrm{Be}$) with Aluminum ($\mathrm{Al}$), and Boron ($\mathrm{B}$) with Silicon ($\mathrm{Silicon}$).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the element that shares a diagonal relationship with Lithium ($\mathrm{Li}$) in the periodic table.

Step 2: Key Formula or Approach:
A diagonal relationship exists between certain elements of the second period (Group 1, 2, 13) and the element located diagonally down to the right in the third period. This anomalous similarity arises due to their closely matching ionic sizes, electronegativities, and charge-to-size ratios (polarizing power).

Step 3: Detailed Explanation:
Let's look at the arrangement of the elements in Period 2 and Period 3:

• Period 2: $\mathrm{Li}$ (Group 1), $\mathrm{Be}$ (Group 2), $\mathrm{B}$ (Group 13)

• Period 3: $\mathrm{Na}$ (Group 1), $\mathrm{Mg}$ (Group 2), $\mathrm{Al}$ (Group 13)
Moving diagonally across from Lithium ($\mathrm{Li}$) in Period 2, we reach Magnesium ($\mathrm{Mg}$) in Period 3. Due to opposing trends across a period and down a group, the ionic radius of $\mathrm{Li^+}$ ($76\ \mathrm{pm}$) is very close to that of $\mathrm{Mg^{2+}}$ ($72\ \mathrm{pm}$). Their polarizing powers are nearly identical, which causes them to exhibit strikingly similar chemical and physical properties (such as forming monoxides instead of peroxides, decomposing carbonates upon heating, etc.).

Step 4: Final Answer:
Lithium shows a diagonal relationship with $\mathrm{Mg}$, which corresponds to option (A).