Question

‘Electron affinity of Na is positive but Mg has negative value’- Why?
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Answer 1

Answer:

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Explanation:

Alkali metals are one electron short of a noble gas configuration. Hence Sodium is more reactive.

While Magnesium being an alkaline-earth metal has two extra electrons to give out.

Electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is “added” to a neutral atom or molecule in the gaseous state to form a negative ion. —

So actually metals as such have an affinity to donate electrons when forming IONICS COMPOUNDS.

The part about electron affinity comes when a metal acts as a Lewis Acid and accepts electrons while forming a Coordination Compound or the so-called “COMPLEXES”

The electrons here are donated by ligands such a NH3, ethylenediamine, etc.

So in this case the stability of the resulting complex usually plays a very important part in determining the electron affinity of a metal like sodium or magnesium.