In this case, since the Lewis dot structure of any element illustrates the number of valence electrons at the outer shell; we can set up the electron configuration of sodium to obtain:
We can see there is only one valence electron, for that reason the Lewis dot structure is:
Roman numeral notation indicates charge of ion when element commonly forms more than one ion. For example, iron(II) has a 2+ charge; iron(III) a 3+ charge.