2. How to Obtain the Number of Sub-Atomic Particles in an Atom Using a Periodic Table ProtonsNeutronsElectrons 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 + + + + + + + + + - = 8 - - - - - - - - + -

3. How to Obtain the Number of Sub-Atomic Particles in an Ion Using a Periodic Table 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 plus the # in the upper right corner if followed by a (-) OR minus the # in the upper right corner if followed by a (+) 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 2- Notice how two electrons have been gained by the atom, thus resulting in an ion + + + + + + + - + + - = 8 10 - - - - - - - - - + -