CK-12 Foundation
Ck 12: Isotopes and Atomic Mass
[Free Registration/Login may be required to access all resource tools.] In the following online tutorial students will be asked to define atomic number, mass number and understand how isotopes differ from one another. They will be able...
Texas Education Agency
Texas Gateway: Ap Physics I: Appendices: Atomic Masses
This is a chart of the elements including the atomic mass, atomic number, symbol, half-life, and more.
Wikimedia
Wikipedia: Atomic Number
Wikipedia provides the definition of the term, "Atomic number," a term used in chemistry and physics to represent the number of protons in the nucleus of an atom.
CK-12 Foundation
Ck 12: Physical Science: Atomic Number
[Free Registration/Login may be required to access all resource tools.] Definitions of atomic number and mass number.
Environmental Chemistry
Environmental chemistry.com: Anatomy of an Atom
Explains the basics of atomic structure, from simple definitions to information about quantum theory. Accurate and helpful basics whether or not you need the more advanced information.
CK-12 Foundation
Ck 12: Physical Science: Atomic Number
[Free Registration/Login may be required to access all resource tools.] Definitions of atomic number and mass number.
California State University
California State University: Proton, Electron, Neutron
An interesting and useful tool to practice recognition/calculation of atomic number, mass, and number of neutrons, electrons, etc. Can be used with all elements.