In class, we learned about the Lewis structure of some elements such as carbon, but we didn't learn how to do the Lewis structure of cations and anions.

Do we just draw the number of electrons in the ion, or do we do something different?

So for example, what would be the Lewis structure of $\ce{Li+}$ and $\ce{Li-}$? How would you draw it out?


1 Answer 1


The charge on a centre in Lewis structures is not of special relevance, except that it helps to provide the information which is useful: the number of electrons on that centre.

A positive charge of $X$ means $X$ electrons were lost, while a negative charge, $-Y$ means $Y$ electrons gained.

From this you can either simply remove/add the corresponding number of dots from/to the diagram, or calculate how many valence electrons are now present, and then draw the diagram ab initio from this information.

A "normal" lithium centre has 1 valence electron, so the positive ion just loses it (leaving no dots) while the negative ion gains one more (and thus has two dots on the diagram).

  • $\begingroup$ @Nij Okay, this may be a somewhat different question, but what would the atom do if it had the same number of electrons added compared to electrons removed to get the $8$ valence electrons? For example, Carbon. It can add $4$ electrons to get $8$ valence electrons, or remove $4$ to get the same number of valence electrons as Helium. Which does it do? $\endgroup$
    – Frank
    Sep 24, 2016 at 3:09
  • $\begingroup$ @frank It tends not to do either. This is where you get the difference between covalent and ionic bonding. $\endgroup$
    – Nij
    Sep 24, 2016 at 3:40

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