How many electrons from the individual : 3 from the hydrogen, and 5 from the nitrogen. So ammonia, ##NH_3##, has 8 to distribute. 6 electrons are utilized for the 3 ##N-H## bonds, and the remaining 2 are localized on the nitrogen as a lone pair. So we get ##:NH_3##. Note that this is not the end of the story. Why have I represented each atom in the molecule as neutral? If I had ammonium ion, ##(NH_4)^+##, the positive charge is associated with the nitrogen centre. For the nitrogen in ammonia, there are 7 positive nuclear charges (i.e. 7 nuclear protons). This charge is balanced by 2 inner core electrons, 2 electrons from the lone pair, and 3 electrons from the ##N-H## bonds (i.e. the other electron in the ##N-H## bond is formally assigned to the hydrogen).