 Okay, now let's try methane. I expect that you can all successfully draw the Lewis structure for methane by now. So let's skip to the chase. How can these four bonds minimize repulsion? Perhaps they stay planar, just like the Lewis diagram. Then there'd be 90 degrees between each pair of bonds. But is there nothing that we could do with this to space them out a bit more? We haven't yet used the third dimension. If we move things around and let two of the bonds point forwards and back, then we can come up with this shape. Imagine a triangle-based pyramid, or tetrahedron. This molecule has the carbon at the very center of the pyramid, and the four hydrogens are at the four vertices. It's just like the chloroform molecule I drew in the last video. This shape is called tetrahedral. And the bond angle between each pair of bonds is 109.5 degrees, which you can see is an improvement on 90 degrees. The bonds are definitely further apart this way than if the molecule was squashed flat like it looks in the Lewis structure. But what's with this drawing here? What's with the weird-looking bonds? Well, this is where I have to introduce you to wedge-diagrams. This is a simple way of drawing molecules so that you can indicate the 3D structure. For methane here, the wedge shape indicates that the bond should be poking out of the page while the dotted bond is receding back into the page. The other two bonds, drawn as ordinary lines, are in the plane of the page. Any time you need to draw a molecule that isn't planar, you can use wedges and dashes to show that.