Introduction to electron configurations

in a previous video we've introduced ourselves to the idea of an orbital that electrons don't just orbit a nucleus the way that a planet might orbit a star but really in order to describe where an electron is at any given point in time we're really thinking about probabilities where it's more likely to be found and less likely to be found and an orbital is a description of that where is it more or less likely to be found and this diagram shows us the types of orbitals which can be found in the various sub shells which are found in the various shells so you have the s subshell the p sub shell that has three different orbitals in it you have the D sub shell that has 1 2 3 4 5 different orbitals in it and then you have the F sub shells now each orbital can fit two electrons so if you're thinking about the sub shell the s subshell can fit two electrons the P sub shell can fit six electrons the d subshell can fit ten electrons and the F sub shell can fit fourteen electrons to per orbital now the goal of this video is to think about electron configurations for particular atoms and to help us with that we will look at a periodic table of elements and so first let's just think about the electron configuration of the simplest element if we're talking about a neutral hydrogen atom a neutral hydrogen atom it has an atomic number of 1 which tells us that has one proton and if it's neutral that means it has one electron now where would that one electron be well it would be in the lowest energy level or the first shell and that first shell has only one sub shell in it it only has one type of orbital it only has an S sub shell and so that one electron in that neutral hydrogen atom would go over there so we would say its electron configuration is 1 a swot in the first shell which is made up only of an S sub shell it has one electron now what happens if we go to helium well a neutral helium atom is going to have two electrons so just having one electron in that first shell we can fit up to two there so its electron configuration it would be 1s2 now what do you think is going to happen when we go to lithium well lithium a neutral lithium will have three electrons in it so the first two could go to the first energy level the first shell so the first two will 1s two and then the third electron is going to go into the second shell and the sub shell that's going to fill first is the s subshell so then it'll go to the second shell and start filling up the s subshell so notice two electrons in the first shell and one electron in the second shell now what about beryllium well that's going to look a lot like lithium but now it has four electrons so two of them are going to go into the first shell one s two and then the next two are going to fill up the s subshell and the second shell and it's a bit of a mouthful to s to notice we have two we have four total electrons which would be the case in a neutral beryllium math atom but what about boron boron gets interesting a neutral boron would have five electrons so the first two are going to fill the first shell 1s two now the second two are then going to go to the second shell and fill up the s subshell two s two and then we're going to start filling up the P sub shell so let's see we have one more electron so we go to P one so you're going to have one electron in one of these P orbitals and then what happens when we go to carbon what's going to look a lot like boron but now we have one more electron to deal with if we have a neutral carbon atom it's going to have six electrons so that elect extra electron is once again going to fall into the p subshell in the second shell because that can fit six electrons so we're going to fill the first shell with two electrons then the two s subshell with two electrons and then we have two more electrons for the 2p sub-shell now you can imagine as we get to larger and larger atoms with more and more electric this can get quite complex so one notation folks often use is a noble gas configuration where instead of saying okay this is carbon they could say that hey look carbon is going to have the electron configuration of helium remember the noble gases are these group 8 elements right over here so it's going to have the electron configuration of helium which tells us this right over here and then from that we're going to also have 2 s 2 2 s 2 and then 2 P 2 you could just take helium's electron configuration right over here and put it right over here and you would get exactly what we wrote before