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Elements and Compounds

Why do you need two sodium atoms for every oxygen atom?

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November 25, 2008 2:04PM

In sodium oxide there are two sodium atoms for each oxygen, formula is Na2O. The reason is that oxygen has a valency of 2 and sodium has a valency of one. They form an ionic compound with two Na+ ions to each O2- . In both of these different sorts of ions the outer electron shell is the same as a noble gas--sodium loses one electron to get the outer shell configuration of Neon and oxygen gains two electrons to get the outer shell configuration of Neon .