1. Neutron Calculations = 16 (P + N) – 8 (P) = 8 N
How to Obtain the Number of Sub-Atomic Particles in an Atom Using a Periodic Table - - - 8 + + -
= 8 + + O + - - + +
Oxygen - - -
Protons
Neutrons
Electrons + -
Equal to the atomic # on the Periodic Table
Equal to the atomic mass (rounded to a whole #) minus the # of protons
Equal to the # of protons
Example: Determine the # of protons, neutrons, and electrons in an atom of oxygen.
Protons = 8 (Atomic #) Neutrons = 8 (Rounded atomic mass minus atomic #) Electrons = 8 (# of P)
Neutron Calculations = 16 (P + N) – 8 (P) = 8 N

2. How to Obtain the Number of Sub-Atomic Particles in an Ion Using a Periodic Table2-
Notice how two electrons have been gained by the atom, thus resulting in an ion + + -
= 8 + - + O + - + + 10 - - -
Neutrons
Protons
Electrons + -
Equal to the # of protons plus the # in the upper right corner if followed by a (-) OR minus the # in the upper right corner if followed by a (+)
Equal to the atomic mass (rounded to a whole #) minus the # of protons
Equal to the atomic # on the Periodic Table -
Example: Determine the # of protons, neutrons, and electrons in the oxygen ion O²¯.
Protons = 8 (Atomic #) Neutrons = 8 (Rounded atomic mass minus atomic #) Electrons = 10
Neutron Calculations = 16 (P + N) – 8 (P) = 8 N Electron Calculations = 8 (e) + 2 (e) = 10 -