Definitions

Atomic Number (Z)   -  the number of protons in the nucleus,  in electrically balanced atom, it is also the number of electrons

Atomic Mass (M)  -  the cumulative average of the following:     the average of the mass numbers of all the isotopes of that element with their natural abundances factored in, along with mass defect and the understanding that the number 1  (1 u) is a comparison to 1/12 of the mass of a carbon-12 atom.

Mass Number (A)  -  the sum of the protons and neutrons that make up that nucleus (or sum of nucleons)

Nucleons  -  particles (of hadron nature) making up the nucleus of atoms (protons and neutrons)

Element  -  a pure form of a substance, made up of one kind of atom, elements are simple substances that cannot be decomposed or transformed into another element by chemical means (you must use physical means such as radiation exposure or particle accelerators)

Atom  -  the smallest particle of an element which possesses the properties of that element

Molecule  -  a substance made up of 2 or more atoms bonded chemically together, has a definite, invariable composition and structure

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