Know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles.
IE, 2,8 and so on for the shells, ie Hydrogen would have 1 in the outer shell, the only electron, Helium would have 2 in the outer shell and the only shell, Lithium would have 2,1 with 1 in the outer shell.
As it is in group 1 we know that there will only be 1 outer shell electron.
