Noble gas configuration

in this video we're going to be talking about how you can write electron configurations using noble gas notation and to be more specific in this video we're also going to be focusing on examples using main group elements so we're doing that because the transition metals right here and the lanthanides are a little bit more complicated so we won't be doing that in this particular video so the rule for writing the noble gas notation for something is pretty simple it is you take the noble gas immediately preceding your atom or ion so what do I mean by immediately preceding that means we want the noble gas that comes right before it so you go up a row and then you go over to here where the noble gases live and you put that in brackets and then you write your other electrons and you write your other electrons using the same notation that you normally write electron configurations in if you don't remember what that is we'll go through a couple examples right now so hopefully it will become more clear so before we get started I'm just gonna remind you why we call the noble gases noble and that is because they have a full octet of electrons and so since they have a full octet they're not very reactive they have all of the electrons they want and as a result you will see in chemistry that a lot of chemistry chemical reactions will be driven by other non noble gases trying to get a full octet so the first example we're going to talk about and write the configuration for is silicon silicon is right below carbon in the periodic table and we can write its full electron configuration just for comparison so if we start up here with hydrogen silicon has the electron configuration 1s2 2s2 2p6 so as a reminder these are RS electrons because they're in s orbitals these are our P electrons because there are P orbitals and then once we're through our 2p 6 electron so you go to 3 s 2 and we have two more electrons so it's 3 P 2 so that's the electron configuration for silicon now we can write it out using noble gas notation and compare so the noble gas immediately preceding silicon if we go up a row and then move over we see that it's neon so we write neon in brackets and then the other electrons are the ones that come after neon so we go down and the electrons that aren't included and neon would be our 3 s 2 electrons right here and the 3 P 2 electrons so if we compare these two ways of writing our electron configuration you can see that these electrons right here so everything up to 3 s 2 3 P 2 that gives us the electron configuration for neon and so we don't have to write that we just write neon and assume that whoever is reading it knows what the left Ron configuration for neon is the other thing you might notice is that these other electrons here that we wrote outside of the brackets these are our valence electrons so writing your electron configuration this way using notebook notation makes it really obvious where your valence electrons are and what kind they are so that's helpful we are going to go through one more example and that will be calcium so calcium is over here and so we're not going to write the full electron configuration this time we're just going to write the noble gas notation so calcium the noble gas immediately preceding it we go up a row and then over and we see that the noble gases are gone so we rewrite argon in our brackets and then what electrons are not in argon so we move down and we see that we have our 4s electrons and we have two of them so this is the noble gas configuration for calcium so does calcium have a full octet and we know that these are the valence electrons and we also know that if it did have a full octet it would actually already have a noble gas configuration so it would either have Krypton or argon and in this case it turns out that calcium prefers to lose two electrons as opposed to gaining a bunch it would be gaining 10 plus 6 so lose two electrons and when calcium loses two electrons it becomes kepta calcium 2 plus cation and then we can write the electron configuration really short or it'll be really short because we know it's gonna lose these two valence electrons and then it will have the electron configuration which is just the same as argon and we can tell really easily looking at this that calcium 2 plus has a full octet so one of the many pros of writing things in noble gas notation besides the fact that it you know makes your hand less tired is that it makes it really easy to see where your valence electrons are and whether or not your ion or atom has a full octet