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Why is gaining electrons called reduction?

Answer 1

In the early days of chemistry, the definitions of oxidation and reduction were respectively, a gain and a loss of oxygen atoms.

For example, #"HgO"# decomposes on heating into mercury and oxygen:

#"2HgO" ⟶ "2Hg" + "O"_2#

The #"Hg"# was said to be reduced because it lost an oxygen atom.

Eventually, chemists realized that the reaction involved a transfer of electrons from #"O"# to #"Hg"#.

#"O"^(2-) → "O" + "2e"^(-) # #"Hg"^(2+) + 2"e"^(-) → "Hg"#

#"Hg"^(2+) + "O"^(2-) → "HgO"#

Since #"Hg"# gained electrons in the process, chemists added a second definition:

#color(red)("G")#ain of #color(red)("E")#lectrons is #color(red)("R")#eduction.

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Answer 2

Elias Aboujaoude

Gaining electrons is called reduction because it involves a decrease in the oxidation state of an atom, resulting in a reduction of positive charge.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.