This document provides a review of key concepts in atomic structure:
1) Protons have a positive charge and determine the atomic number, neutrons have no charge and determine isotope variations, electrons have a negative charge and determine ion charge state.
2) Atomic mass is the total number of protons and neutrons, while the atomic number indicates just the number of protons. Neutrons can be calculated by subtracting the atomic number from atomic mass.
3) Elements are arranged on the periodic table by atomic number, which identifies each unique atom, while isotopes of an element can vary in neutron number.