How to Draw Lewis Dot Structures for Ionic Compounds/Bonds

When drawing Lewis Dot Structures for ionic compounds you need to follow a different set of rules than with Lewis Structures for covalent/molecular compounds. This is because valence electrons are transferred when ionic bonds form. This transfer of electrons (unlike covalent compounds where valence electrons are shared) needs to be addressed when drawing the structure.

Ionic compounds are made of a metal and a non-metal (or a metal and a group of non-metals). The metal transfers electrons to the non-metal(s). To show this we put brackets around the non-metal that gains the valence electrons. For simple binary ionic compounds, like NaCl or K2O, this is straightforward.

For ionic compounds with polyatomic ions, like NaNO3 or K2SO4, we need to draw the Lewis Structure for the polyatomic (which is usually a covalent compound where valence electrons are shared) and then place this with the metal in a Lewis Structure for the ionic compound. In effect you are drawing two Lewis Structures.

Useful Videos:
• Identifying Metals and Non-Metals: youtu.be/OoooStZQHdA
• Finding Number of Valence Electrons: youtu.be/x1gdfkvkPTk
• Polyatomic Ions: youtu.be/vepxhM_bZqk
• NO3- Lewis Structure: youtu.be/hN4EFQkgnAo
• How to Draw Lewis Structures: youtu.be/1ZlnzyHahvo

Note that is it more common to draw Lewis Structures for covalent (molecular) compounds where valance electrons are shared. In the case of ionic compounds, where we have a metal bonded to a non-metal (or group of non-metals), the Lewis diagram represents a formula unit. Many of these formula units make up a crystal lattice. So when we talk about the structure for something like NaCl we think of it together with other NaCl formula units in a crystal (see: en.wikipedia.org/wiki/Sodium_chloride).


NaCl crystal image: By Benjah-bmm27 [Public domain], from Wikimedia Commons. commons.wikimedia.org/wiki/File:Sodium-chloride…