How many more elections are needed to fill the outermost energy level?

To determine how many more elections are needed to fill the outermost energy level of an atom, you need to know the number of electrons already present in that level and the maximum capacity of that level. The outermost energy level can hold a maximum of 8 electrons (following the octet rule) for main group elements. Subtract the number of existing electrons from 8 to find out how many more are needed to fill the level. For example, if there are 5 electrons in the outermost level, 3 more are needed to fill it.