Question

which element has the largest ionic size in each pair? 1. mg or mg2+? 2. o or o2 -? 3. li or li+1? 4. cl or cl-?

Explanation:

Step1: Recall ionic - size trends

The ionic size depends on the number of electron - shells and the nuclear charge. For isoelectronic species, the ion with the smaller nuclear charge has a larger ionic radius. For non - isoelectronic species, more electron - shells mean larger size.

Step2: Compare Mg and Mg²⁺

Mg has 12 electrons and 3 electron - shells (1s²2s²2p⁶3s²), while Mg²⁺ has 10 electrons and 2 electron - shells (1s²2s²2p⁶). So, Mg > Mg²⁺.

Step3: Compare O and O²⁻

O has 8 electrons (1s²2s²2p⁴) and O²⁻ has 10 electrons (1s²2s²2p⁶). When an atom gains electrons to form an anion, the electron - electron repulsion increases and the ionic radius increases. So, O²⁻ > O.

Step4: Compare Li and Li⁺

Li has 3 electrons (1s²2s¹) and Li⁺ has 2 electrons (1s²). Losing an electron reduces the electron cloud, so Li > Li⁺.

Step5: Compare Cl and Cl⁻

Cl has 17 electrons (1s²2s²2p⁶3s²3p⁵) and Cl⁻ has 18 electrons (1s²2s²2p⁶3s²3p⁶). Adding an electron increases the electron - electron repulsion and the ionic radius, so Cl⁻ > Cl.

Answer:

1. Mg
2. O²⁻
3. Li
4. Cl⁻