in this video you'll learn to write condensed electron configurations so we'll start off with an example give you some practice and by the end of the video you'll be a pro at writing these condensed electron configurations let's start with bromine so this is the full electron configuration for bromine you'll note we have 35 protons so we'll have 35 electrons since this is neutral we can condense this by finding the noble gas before bromine here's bromine so we go back and find argon and then argon has 18 electrons there we go this is the noble gas core we just write argon and then the rest of these electrons here that'll look like this and that's how you write condensed electron configurations so let's get some practice and talk about some of the finer details with these condensed electron configurations so this is the electron configuration for lithium lithium has an atomic number of three that's the number of protons because it's neutral it has three electrons two plus one that gives us three if you need help writing these electron configurations there's a link in the description and at the end of the video so lithium is right here on the periodic table we can see that the first energy level that one there that has two in it but it's full after you get one two you have to go to the next energy level and that would be the 2s 1. these numbers need to add up to 3. if we want to write the condensed electron configuration we have lithium so we go back to the noble gas before it that's helium and helium is the 1s2 we just put this in brackets and that would give us a condensed electron configuration that looks like this didn't really save us much trouble but lithium that's the simplest condensed electron configuration there is so pause and try this one here's the full electron configuration for carbon has six protons so six electrons here you write the condensed electron configuration for carbon so we find carbon on the periodic table we go back to the noble gas before it that's helium again so we put our brackets around this and right this is our condensed electron configuration let's try something a little bit longer pause and write the condensed electron configuration for calcium and note calcium right here this is calcium so you're going to go back to the noble gas before so we're at 20 atomic number 20 we go back to 18 argon so we'd find 18 electrons here that would be like this so everything in here is the electron configuration for argon we call this our noble gas core here's our valence electrons so the condensed notation that'll look like ar in brackets 4s2 again these are our valence electrons now we're getting somewhere this is starting to save us some time what happens if we have an ion though something like ca2 plus so when we have an ion like ca2 plus this plus this two plus means we've lost two electrons so we're just going to take away two electrons from our configuration up here so our electron configuration for ca2 plus that's just the same as argon it's still calcium we still have 20 protons but we've lost those two electrons to form the calcium ion and the actual configuration of electrons same as calcium very stable but rather than just crossing this out let's make it 4s 0. that makes it a little clear that we've lost valence electrons if you had a negative ion something like n3 minus you would just add 3 electrons to your configuration let's try a really long one so for iodine we have 53 protons and because it's neutral 53 electrons if you count all these up 53 electrons so pause and try to write the condensed electron configuration for iodine so here's iodine right here if we go back we get krypton so we're going to have kr kr has 36 electrons so we find 36 electrons here that's right here so we'll just write kr in place of all this and we end up with our abbreviated electron configuration for iodine there's something interesting happening here though now we have these d orbitals 4d10 so we consider all of these to be valence electrons except the d orbital it's full with 10 so this doesn't usually take place in chemical reactions when we look at our noble gases in general they don't react except under extreme conditions things like krypton and xenon they can react because of these d orbitals so under high temperature and pressure sometimes you can get things like krf2 or xeo4 so they will form some compounds these guys down here because of the d orbitals all right one last one write the condensed electron configuration for barium and barium that's right here on the periodic table so we find the noble gas before barium is 56 55 here we go 54 xenon so we count up to 54 that's from here to all the way over here so for to write the electron configuration in its condensed or abbreviated form for barium that'll look like this so we have two valence electrons in this 6s2 so we go down 1 2 3 4 5 six there's the six energy level there's barium in group two so that makes sense it should have two valence electrons just like all these elements in group two so writing these condensed electron configurations also called abbreviated configurations it really helps us see these valence electrons clearly from all of this and it also saves us a lot of time in not writing out this big configuration each time when we could just write xc 6s2 for barium this is dr b with how to write condensed electron configurations thanks for watching