How do you work out an electron configuration?
A full electron configuration shows the amount of electrons in each shell and subshell of an element or ion. Shells (also called energy levels) progress from 1 to 4, with 1 being the closest to the centre of the atom or ion and 4 being the furthest away. We usually fill from the inside out. Shell 1 can hold a maximum of 2 electrons, for shell 2 this is 8, for 3 this is 18 and for 4 this is 32 (although you won't need to work out any shell 4 for A Level).The Electron subshells progress from s to p to d to f. At A Level the highest a question will ask you to go up to is d subshell. A s subshell can hold up to 2 electrons, a p subshell can hold up to 6 and a d subshell can hold up to 10. We work up the subshells in order from s to p to d, with a slight exception I will mention later. So, with the maximum number of electrons able to be held in shell 1 being 2, there is one s subshell in shell 1. Shell 2 can hold 8 electrons which means it contains both an s subshell and a p subshell. Shell 3 can hold 18 electrons, representing a s, p and d subshell.So, for example, if we were to show the electron configuration of carbon, which has 6 electrons, we would demonstrate it like this: 1s2 2s2 2p2
