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The atomic number of Na is 11 (2, 8, 1). Na loses an electron to achieve octet stability but why can't it just accept an electron to complete duplet stability?

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    $\begingroup$ Why, of course it can. The problem is, there are not enough free electrons for everyone. $\endgroup$ – Ivan Neretin Feb 9 '17 at 8:05
  • $\begingroup$ @Ivan Neretin Would you elaborate "there are not enough free electrons for everyone. "? $\endgroup$ – Mockingbird Feb 9 '17 at 9:26
  • $\begingroup$ I mean, all $\ce{Na}$ can't convert to $\ce{Na-}$. But I guess that's not what the question was about, anyway. $\endgroup$ – Ivan Neretin Feb 9 '17 at 9:34
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    $\begingroup$ Possible duplicate of Is it possible to have a diatomic molecule of sodium in gaseous state? $\endgroup$ – bobthechemist Feb 9 '17 at 13:12
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    $\begingroup$ @bobthechemist The questions are completely different even though they might have a similar answer. It is absolutely not the same asking "Why doesn't it accept an electron?" and "Does a dimer exist?" $\endgroup$ – Martin - マーチン Feb 9 '17 at 14:39
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Well, sodium does have non-zero electron affinity, so it surely can acquire another electron, provided it can get one for free. That's what happens when a lone sodium atom meets a lone electron somewhere in deep space. But here on Earth, with all that condensed matter around, we don't have many free electrons (*). They all belong to some other atoms, and if you want to get an electron (that is, to get reduced), you have to oxidize something else.


(*) Then again, some might recall metals in which the electrons are kinda free, but wait: they are not really free. They are bound by the collective field of metal cations, and you need to apply certain energy to take one out.


It turns out that $\ce{Na}$ and other alkali metals can actually be reduced to form alkalides, but those are exotic compounds. They are not particularly stable, and get oxidized with pretty much anything. It is much easier for $\ce{Na}$ to form a cation, thus achieving the stable octet, and call it a day.

There is a whole different dimension to the problem: why wouldn't two sodium atoms share their electrons, establish a bond, and form a diatomic molecule? Again, they would, but only in a vacuum! When you have many such molecules, the sodium atoms would share their other empty orbitals, find out they don't have enough electrons to fill them all, and just resort to being a metal.

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