When it comes to three electron groups, we're going to say this is when central elements with three electron groups that can have either zero or one lone pair to get two possible molecular geometries. So again, when we have 3 electron groups around our central element, 2 possible shapes can occur. So we have 3 electron groups.
In the first situation we have 3 surrounding elements, or three bonding groups and 0 lone pairs. Here we have an example of carbon in the center connected to three surrounding elements. Its visualization would look like this and we'd say that it's molecular geometry would be trigonal planar.
Now another option that could occur is we have two surrounding elements or two bonding groups and 1 lone pair on the central element. Here we have our example with tin in the center with two chlorines and it has one lone pair. In its visualization we have lost the element that was here and it's been replaced by a lone pair.
Now remember, lone pairs have an electron cloud which further causes more repulsion. So that's why it looks kind of like that, and its shape kind of fits the name here. We'd say that its molecular shape is bent. You might also see the name V shaped or you might even see the name angular. So just remember all of these names are synonymous for the same thing.
They're talking about a molecular structure in this case where we have two surrounding elements and 1 lone pair in terms of this one and other ones like it right. So keep in mind when you have 3 electron groups around your central element, 2 possible molecular geometries are possible.
