Chemical Bonding: Lewis Dot Structure for CH4 (2 of 6)
Dr. B. explains how to draw the Lewis dot structure for CH4 (methane). The CH4 Lewis Structure is one of the most frequently tested Lewis Structures.
Note that hydrogen atoms always go on the outside of a Lewis dot structure. This is because they can share a maximum of two electrons. Once they have two valence electrons their outer shell is full (they have an octet although it's probably more appropriate to call it a duet here).
Video: Draw the Lewis Dot Structure for CH4.
Answer the Questions about the CH4 Lewis Dot Structure to Aid Memory.
CH4 Lewis Structure: Video Transcript
We're going to draw the dot structure for CH4, Carbon Tetrahydride, also called Methane. And what we need to do is follow the steps you see on the screen there. These are abbreviated steps since CH4 is pretty straight forward.
The first thing that we need to do is to take and count the number of valence electrons, so here's CH4. And to do that I've got to look on the periodic table.
I can see that H is in Group 1, and if we come over here Carbon is in Group 4. That's how we determine the number of valence electrons. I have 4 valence electrons, outer shell electrons for Carbon, plus 1 of Hydrogen. But there are 4 Hydrogens so 4 plus 4(1) equals 8. So I have a total of eight valence electrons.
After that I need to put the least electronegative at the center. And on the periodic table that means the one that is furthers from Fluorine will go at the center. But here we note that Hydrogen always goes on the outside. So we'll draw our structure with a Carbon and the Hydrogens always on the outside.
After we do that we have 8 electrons that we need to spread around there. Assign 2 electrons to each bond. That means put them between each of the 2 atoms that are next to each other. I only have eight, and I actually ended up using all 8 of them. You want to complete the octets on the outside. But since Hydrogen has two we don't need to do anything and we don't have any electrons to spare.
Let's check and see if everything has full outer shells or octets. Carbon has 4 pairs, so it has eight electrons. That octet is satisfied. And each Hydrogen has 2. So for Hydrogen that octet is also satisfied. So by sharing the electrons, each one of the atoms involved ended up having full outer shells which makes them very stable and they are at a much lower energy, partially related to the stability.
That's a pretty easy one, we'll go on next and do a little more complicated dot structure.
The Lewis dot structure for CH4 shows the number of valence electrons around each atom.
Each dot represents a valence electron.
The number of valence electrons is the same in the group and equal to the group number.