The Atomic Number
The atomic number (symbol: Z) of an atom is the number of protons in the nucleus of the atom. Atoms of each element contain a characteristic number of protons, the number of protons in an atom is called the atomic number. The atomic number of an atom identifies which element it is. For example, An atom of iron has 26 protons in its nucleus; therefore the atomic number of iron is 26. In a neutral atom, the atomic number is equal to the number of electrons orbiting the nucleus. The elements of the periodic table are listed in order of increasing atomic number. The atomic number is not the same as: Atomic mass (symbol: ma), which is the mass of a single atom, commonly expressed in unified atomic mass units Mass number (symbol: A), which is the sum of the number of protons and number of neutrons in the nucleus of an atom Relative atomic mass (also called atomic weight; symbol: Ar), which is the ratio of the average mass per atom of an element from a given sample to 1/12 t...