Question

which element has the largest ionic size in each pair? 1. al or al^3+? 2. s or s^2 -? 3. na or na^+1? 4. i or i^-1?

Explanation:

Step1: Recall ionic - size trend

Ionic size depends on the number of electron shells and the nuclear charge. Cations are smaller than their parent atoms and anions are larger than their parent atoms. Also, for ions with the same number of electrons (isoelectronic species), the ion with the greater nuclear charge is smaller.

Step2: Compare Al and Al³⁺

Al has 13 electrons and Al³⁺ has 10 electrons. When Al loses 3 electrons to form Al³⁺, the remaining electrons are pulled closer to the nucleus due to the increased effective - nuclear charge. So, Al > Al³⁺.

Step3: Compare S and S²⁻

S has 16 electrons and S²⁻ has 18 electrons. When S gains 2 electrons to form S²⁻, the electron - electron repulsion increases and the electron cloud expands. So, S²⁻ > S.

Step4: Compare Na and Na⁺

Na has 11 electrons and Na⁺ has 10 electrons. When Na loses 1 electron to form Na⁺, the remaining electrons are pulled closer to the nucleus. So, Na > Na⁺.

Step5: Compare I and I⁻

I has 53 electrons and I⁻ has 54 electrons. When I gains 1 electron to form I⁻, the electron - electron repulsion causes the electron cloud to expand. So, I⁻ > I.

Answer:

1. Al
2. S²⁻
3. Na
4. I⁻