Chemical Bonding: CH₃^- Lewis Structure

Drawing the Lewis Structure for CH₃^-

Viewing Notes:

• The CH₃^- Lewis structure has a total of 8 valence electrons. This includes the electron represented by the negative charge in CH₃^-.
• You need to put brackets around the CH₃^- Lewis structure as well as a negative charge to show that the structure is a negative ion.
• If you calculate the formal charges for CH₃^- you'll find that the Carbon (C) has a -1 charge and the Hydrogen (H) atoms each have a formal charge of zero. This gives the entire structure a -1 charge (remember it's CH₃^-).

Transcript: This is the CH3- Lewis structure. On the periodic table, Carbon has 4 valence electrons. Hydrogen has 1, but we have three Hydrogens. Then we have this negative up here so we need to add an additional valence electron for a total of 4 plus 3 plus 1: 8 valence electrons. We'll put the Carbon in the center. Hydrogen always goes on the outside. We have three of them, just put them around like this. We'll put two valence electrons between the Hydrogen and the Carbon in each case to form chemical bonds. We've used 2, 4, 6 valence electrons. We have 8, so we'll put the remaining two here on top of the Carbon.

Hydrogen only needs 2 valence electrons for a full outer shell, and each Hydrogen in this structure has two valence electrons. Carbon needs 8 for an octet, and it has 8 as well. If you calculate the formal charges for the Carbon, you'll see that it's a negative one formal charge on the Carbon. The Hydrogens have a formal charge of zero. And that negative makes sense because we have a negative up here.

So this is the Lewis structure for CH3-. This is Dr. B., and thanks for watching.