An electron shell is what surrounds the nucleus of the atoms. The nucleus contains protons and neutrons and is the heaviest part of the atom. Electrons closer to the nucleus will have not have as much energy as the electrons in the outer shells. The first shell can only have two electrons. The second can have 8, of the eight that is broken into sub shells there can be 2 s electrons and six p electrons. The fourth shell or what is also called the valance shell has four subgroups that are s,p,d, and f and all together can have a maximum of 32 electrons. A subsequent shell or sub shell is each electron shell broken into groups. These groups make it so when writing out how many electrons are in atoms you can distinguish how many there are. Along with this, there is a process on how to write these out. The order would be 1s,2s,2p,3s,3p, 4d, 3d, 4p, and so on.
