why mg2+ has smaller size (65pm) as compared to Na+(95pm) although both have the same Noble gas configuration
Answers
Answer:
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Explanation:
Mg2+ ion is smaller than O2- ion though both are iso-electronic. The nuclear charge in Mg2+ is + 12 and O2- is + 8, so with the increase in nuclear charge the size decreases and, hence O2- > Mg2+.
Answer:
Please remember as a rule that if we are given a neutral atom X, then radius order or size order is-
X⁻² > X⁻¹ > X > X⁺¹ > X⁺²
This will help in problems.
Now we come to your question.
Mg⁺² and Na⁺ both have Ne configuration, however Mg⁺² has smaller size than Na⁺. This can be explained by the concept of effective nuclear charge, which states that greater the positive charge on the ion, more is the attractive force towards the nucleus.
We know that if any two particles experience an attractive force towards one another, they have a tendency to come closer. Therefore, the nucleus pulls the electrons in the valence shell towards itself and that reduces the size of the ion. This happens more for Mg⁺², as can be observed.