Question 5 of 48intermediate🔧 ApplyShort Answer2 marks

Which of the following species will have the largest and the smallest size? Mg, Mg²⁺, Al, Al³⁺.

Correct Answer

The largest species is Mg, and the smallest species is Al3+Al^{3+}.

Exercise: IN-TEXT QUESTIONS (PROBLEMS) | Q: Problem 3.5 | (Page 15)
For More Understanding

Explanation

Atomic radii decrease across a period, so Mg is larger than Al. Cations are smaller than their parent atoms, so Mg2+Mg^{2+} is smaller than Mg and Al3+Al^{3+} is smaller than Al. The ions Mg2+Mg^{2+} and Al3+Al^{3+} are isoelectronic species (10 electrons each). Among isoelectronic species, the one with the larger positive nuclear charge has a smaller radius. Since Al has a greater nuclear charge than Mg, Al3+Al^{3+} is smaller than Mg2+Mg^{2+}. Therefore, Mg is the largest and Al3+Al^{3+} is the smallest.

Solution Steps

  1. Step 1: Compare the neutral atoms. Atomic radii decrease across a period, so Mg is larger than Al.

  2. Step 2: Compare atoms with their ions. Cations are smaller than their parent atoms, so Mg2+Mg^{2+} is smaller than Mg, and Al3+Al^{3+} is smaller than Al.

  3. Step 3: Compare the two cations. Mg2+Mg^{2+} and Al3+Al^{3+} are isoelectronic species. The one with the larger positive nuclear charge (Al3+Al^{3+}) will have a smaller radius.

  4. Step 4: Conclude that the largest species is Mg and the smallest is Al3+Al^{3+}.

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