in this video I want to tell you how you can calculate valence electrons but also to understand it as well so let's look at an atom of nitrogen so nitrogen has an atomic number of seven and an average atomic mass of fourteen point zero one so an atom of nitrogen has seven protons and seven electrons atoms are electrically neutral now let's draw a simple Bohr model of the nitrogen atom in the first shell or the first energy level nitrogen carries two electrons that's the maximum number of electrons you could have in a first energy level in the second energy level you could have up to eight electrons but what we have is a total of seven so we need to place five and the second energy level so we could have a total of seven the valence electrons are the electrons in the outermost energy level so therefore a nitrogen has five valence electrons so here are the five valence electrons of the nitrogen atom now the inner shell electrons the ones on the inside the ones that are not valence electrons these are known as core electrons so nitrogen contains two core electrons for a total of seven electrons which is which goes with the atomic number of nitrogen now keep in mind for atoms the number of protons and electrons are the same but for ions they differ so you have to adjust the base on a charge now let's look at another example let's consider the aluminum atom which has an atomic number of 13 and an average atomic mass of 26 point nine eight how many valence electrons and core electrons can be found in the aluminum atom so let's draw a picture so this is gonna be the first shout and this is the second energy level and this one is gonna be the third so in the first energy level there's gonna be two electrons now we said the second can hold a maximum of eight electrons so right now we have a total of ten but we need to get up to 13 so that's 13 so aluminum has three valence electrons those are the electrons in the highest energy level now how many core electrons does have it has two in the first shell and then eight in the second shell so it has a total of ten core electrons if you add ten plus three you're gonna get the atomic number for the atom thirteen electrons in total so just make sure you understand is the valence electrons are the electrons in the outermost energy level these are the electrons that participate in a chemical reaction the inner core electrons for the most part really participate in a chemical reaction it's the valence electrons that are involved in reactions that we see in a day-to-day basis now another way in which you can identify the number of valence electrons it is by writing the electron configuration so let's write it for nitrogen and for aluminum the electron configuration for nitrogen I'm assuming that you already know how to do this if not you can check out another video that have on YouTube it's 1s2 2s2 2p3 so notice that the exponents add up to seven because nitrogen has a total of seven electrons now in the highest energy level that's in the second energy level we have two sub levels 2s and 2p but in the second energy level notice that we have a total of five electrons so those five are the five valence electrons those are the electrons in the outermost or the highest energy level all the other electrons are known as core electrons so you can see that nitrogen has two core electrons now let's consider aluminum the electron the figuration is 1s2 2s2 2p6 3s2 3p2 on the s sublevel can only hold two electrons P can hold up to six electrons and D can hold up to ten but we look at the highest energy level of aluminum which is the third energy level we could see that there are three electrons there two plus one extreme so aluminum contains three valence electrons all the others represent core electrons so we got two plus two plus six so aluminum contains ten core electrons so that's how you can identify the number of valence electrons in core electrons using the electron configuration now let me give you another example let's use chlorine which has an atomic number of 17 so in an atom of chlorine write the electron configuration and then identify the number of core and valence electrons so the electrical figuration of chlorine is 1s2 2s2 2p6 3s2 3p5 all the exponents out of 17 so the valence electrons are the electrons in the highest energy level so in the case of chlorine we have two plus five so seven valence electrons and the rest our core electrons so we've got a total of ten core electrons another way in which you can identify the number of valence electrons is using the periodic table you can identify it based on a group number of Representative elements so in group number one we have elements like hydrogen lithium sodium potassium these elements all have a valence electron of one they have one valence electron now in the second group you have the alkaline earth metals like beryllium magnesium calcium so these metals have two valence electrons they're in group 2 of the periodic now we're gonna skip the transition metals and move on to group 13 also known as group 3a so these include aluminum and gallium and I believe indium is the next one so these elements have three valence electrons and I'm forgetting something can't forget about boron after boron is aluminum then we have helium so these elements contain three valence electrons and then after born you have carbon silicon germanium and those elements contain four valence electrons and then you have nitrogen phosphorus and I believe arsenic so these they're found in group five a so they contain five valence electrons then you have the chalcogen like oxygen sulfur selenium these guys they hold up to six valence electrons and then you have the halogens like fluorine chlorine bromine iodine those guys they have seven now be careful of this one helium is a noble gas but it only has two valence electrons because it has a total of two electrons so here having but the other ones after it like neon and I think it's a argon krypton all of these they have eight valence electrons now I have another question for you let's focus on iodine which has an atomic number of 53 and an average atomic mass of 120 6.9 now how many core electrons are found in an atom of iodine think about it now you can use any one of the techniques that we've illustrated in his video you can draw the Bohr model of the atom which is gonna take time to draw 53 electrons you can also write out the electron configuration which works as well but because iodine is a relatively large atom it's going to take some time to draw the electrical figuration so is there an efficient way to determine the number of core electrons what's the easiest way to quickly give the answer now we can start with an equation the total number of electrons is equal to the sum of the core electrons plus the valence electrons keep that in mind now for an atom of iodine we have 53 electrons in total now in order to find the core electrons we need to find the valence electrons first now we could do so by using the group number iodine is in group 7a it's a hill agem so it contains seven valence electrons so the number of core electrons is simply the total number of electrons which you can find a base on the atomic number of an atom minus the valence electrons found by the group number so it's gonna be 53 minus seven which is 46 core electrons because 46 plus seven is 53 and so that's an efficient way to find the number of core electrons when you're dealing with an element that's pretty large you don't want to draw it out over at out the electron configuration that's gonna take time so just identify the atomic number and the group number subtract those two and that will give you the number of core electrons