Which one of the following species has the same electron configuration asthe Al3+ cation?A F –B Cl–C S2– D O– E Mg+
The Correct Answer and Explanation is:
Correct Answer: E. Mg⁺
Explanation (300+ words):
To determine which species has the same electron configuration as the Al³⁺ (aluminum ion), we must first understand the electron configuration of a neutral aluminum atom (Al) and how it changes when it loses electrons to form Al³⁺.
Step 1: Electron Configuration of Neutral Aluminum (Al)
- Aluminum has an atomic number of 13, meaning it has 13 electrons in its neutral state.
- The ground-state electron configuration is: $$
\text{Al}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^1
$$
Step 2: Electron Configuration of Al³⁺
- Al³⁺ means that aluminum has lost three electrons.
- These electrons are removed from the outermost energy level (first from 3p and then 3s orbitals).
- So we remove the 3p¹ and 3s² electrons, leaving: $$
\text{Al}^{3+}: 1s^2 \, 2s^2 \, 2p^6
$$ - This configuration corresponds to a total of 10 electrons, the same as a neon (Ne) atom (noble gas with atomic number 10).
Step 3: Find Which Species Also Has 10 Electrons
Now, evaluate each answer choice:
- A. F⁻ (Fluoride ion):
Fluorine has 9 electrons. F⁻ gains 1 electron → 10 electrons.
✓ Possible match. - B. Cl⁻ (Chloride ion):
Chlorine has 17 electrons. Cl⁻ has 18 electrons.
✗ Too many electrons. - C. S²⁻ (Sulfide ion):
Sulfur has 16 electrons. S²⁻ has 18 electrons.
✗ Too many electrons. - D. O⁻ (Oxide ion):
Oxygen has 8 electrons. O⁻ has 9 electrons.
✗ Too few electrons. - E. Mg⁺ (Magnesium ion with a +1 charge):
Magnesium has 12 electrons. Mg⁺ has lost 1 electron → 11 electrons.
✗ Too many electrons.
Wait — there’s a mistake here. The question asked which one has the same configuration as Al³⁺, which has 10 electrons.
Let’s re-check:
- A. F⁻ → 10 electrons → Configuration: 1s² 2s² 2p⁶ ✔️
So the correct match is F⁻, not Mg⁺.
✅ Corrected Answer: A. F⁻
Final Explanation:
Both Al³⁺ and F⁻ have 10 electrons, giving them the same electron configuration: 1s² 2s² 2p⁶. This configuration is isoelectronic with neon, a noble gas. Isoelectronic species have the same number of electrons and hence the same electron configuration, although their nuclear charges differ.
Thus, the species with the same electron configuration as Al³⁺ is F⁻.
