 So we've done an example but now I need to tell you about some exceptions, there are always exceptions. The part of the process that the exceptions refer to are the bit where you're checking whether all of your atoms have a noble gas configuration. So the first exception is this. If you have a structure that has beryllium or boron in these are known as electron deficient atoms which means they don't have to have a full octet. They don't need to have eight electrons in their outer shell. Beryllium typically forms two bonds and boron typically forms three and they don't need any extra electrons. Now if you noticed anything odd about this, yes boron and beryllium we usually think of them as being metals but the universe is not black and white. Some metals are able to cross the boundary and form covalent bonds under certain circumstances. Our second exception are non-metals in period three and below. So that's things like sulfur and phosphorus and chlorine and bromine and so on. These guys are what's called hypervalent meaning they can actually have more than eight electrons in their outer shell. The reason is that because they're in period three and their outer shell is now the third electron level they have access to d orbitals which the period two elements don't. This is a bit like having extra pockets to keep your electrons in. So a molecule like sulfur hexafluoride is possible. Sulfur is able to form six bonds which gives it 12 valence electrons. So those are our main exceptions. What this means is that there's actually a relatively limited number of atoms where you need to be strict about them having an exactly full outer shell and they are hydrogen which must have two and carbon, nitrogen, oxygen and fluorine which must have eight. Weirdly pretty much everything else is an exception.