As sodium ion has a 1+ charge and it can form the ionic compound NaOH with OH1-, hence it is a lone pair accepter (is this correct?). Therefore sodium ion should be an acid?

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    $\begingroup$ Yes, it's a Lewis acid, but a weak one. $\endgroup$
    – Mithoron
    Sep 15, 2018 at 18:22
  • $\begingroup$ But $\ce{Na+}$ isn't an acid in the Brønsted–Lowry theory, so it depends... $\endgroup$
    – MaxW
    Sep 15, 2018 at 23:33
  • $\begingroup$ I thought sodium was in part of the alkali metals,but ions clearly don't work the way you think they're supposed to,but yes it's technically and "acid". $\endgroup$ May 22, 2021 at 21:26

2 Answers 2


Sodium ion in aqueous chemistry is essentially nonacdic (contrast this with lithium ion, which displaces carbon dioxide when the bicarbonate is "precipitated" and the precipitate is actually lithium carbonate). But in organic chemistry sodium ion shows some Lewis acid character, as demonstrated in the incompletely ionic structure and the solvation of sodium cyclopentadienide:

The nature of $\ce{NaCp}$ depends strongly on its medium and for the purposes of planning syntheses; the reagent is often represented as a salt $\ce{Na^+C5H5^-}$. Crystalline solvent-free $\ce{NaCp}$, which is rarely encountered, is a "polydecker" sandwich complex, consisting of an infinite chain of alternating $\ce{Na^+}$ centers sandwiched between $\ce{μ-η5:η5-C5H5^-}$ ligands.[1] As a solution in donor solvents, $\ce{NaCp}$ is highly solvated, especially at the alkali metal as suggested by the isolability of the adduct $\ce{Na(tmeda)Cp}$.[2]

Cited References

  1. Robert E. Dinnebier; Ulrich Behrens & Falk Olbrich (1997). "Solid State Structures of Cyclopentadienyllithium, -sodium, and -potassium. Determination by High-Resolution Powder Diffraction". Organometallics. 16 (17): 3855–3858. doi:10.1021/om9700122.

  2. Elschenbroich, C. (2006). Organometallics. Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2.


According to the bronsted lowry definition of an acid, the sodium ion is not an acid. This is because the bronsted lowry definition of an acid states that an acid is a proton donor. The sodium ion is not a proton donor and so according to this definition it is not classed as an acid.

I hope this answers your question :)

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    $\begingroup$ But the question doesn't specify Bronsted-Lowry. It actually has descriptions related to Lewis and Arrhenius acids, so the Bronsted-Lowry definition is the least related to the question. $\endgroup$ Sep 26, 2018 at 19:42
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    $\begingroup$ But in water the ion will be hydrated, and the hydrated ion can most definitely act as a (weak) Bronsted-Lowry acid $\endgroup$
    – Ian Bush
    Sep 26, 2018 at 21:05
  • $\begingroup$ @IanBush exactly $\endgroup$ May 22, 2021 at 21:29

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