Sodium is the 11th element in the periodic table so it will have 11 electrons (if you're not sure if something is right always check how many electrons they're are it's like checking your work in math). There are 4 energy "types" in the periodic table: S,P,D and F. Starting from the top left you are in the first energy level 1 (in the S area which is always the first two elements on the left of the table before the transition metals) and there are two elements (hydrogen and helium) so you have 1s^2 then you go down to the second column and you have the first two elements which are Lithium and Beryllium so your next config is 2s^2. Now you have more elements on the left and those are in the "P energy section" and there are 6 elements there so you put 2p^6. Now you move down again and you're in the 3rd energy level and sodium is the 1st element and so you only need to put 3s^1. Your econfig is 1s^2 2s^2 2p^6 and 3s^1
