A bond angle represents the angle between two bonds that originate from the same element within a molecule. So, if we take a look at this, we have here our central element and it's connected to two surrounding elements. The bond angle would be the distance from here to here. Here is our central element. So, the bond angle will be the distance from here to here.

And then finally, if we have a lone pair involved, we are going to ignore the lone pair. We're looking at the bond between the central element and the two surrounding elements. So, the bond angle will be here to here. Now, we're going to say when the central element has zero lone pairs, it possesses an ideal bond angle like this example in this example here. We're going to say that the ideal bond angles is the optimal angle elements take in order to minimize repulsion between one another. So, it's that perfect angle they take when the central element has no lone pairs on it.

And what we need to realize here is that when a central element has one or more lone pairs, its ideal bond angle will be decreased. So, if we took a look here at this third one, because our central element possesses a lone pair, what this lone pair does is it pushes the bonds further away from itself, causing them to come closer and tighter together. So, we'd expect the bond angle here to be different from the bond angle here, although both look kind of V-shaped or bent, their bond angles would not be the same because again the lone pairs push for more repulsion. They push those bond angles slightly closer together, causing a decrease in our bond angle.

So, keep this in mind when our central element has no lone pairs, we're going to have a perfect ideal bond angle, but once it starts gaining lone pairs, that ideal bond angle no longer exists, and the angle itself starts to get smaller and smaller in value.