Chemistry (7th Edition)

("P" = Number of protons; "$e^-$ = Number of electrons"; "N" = Number of neutrons) 1. Number of protons: $P = Z$ (Atomic number) (Bottom left number); (a) 7 (b) 27 (c) 53 (d) 58 2. Number of electrons $e^- = P$ (because they are neutral) (a) 7 (b) 27 (c) 53 (d) 58 3. Number of neutrons: Each proton and neutron is responsible for 1 unit of mass: $P + N = A$ ("A" is the top left number) Therefore: $N = A - P$ (a) $N = 15 - 7 = 8$ (b) $N = 60 - 27 = 33$ (c) $N = 131 - 53 = 78$ (d) $N = 148 - 58 = 90$