Hydrogen, nitrogen, oxygen, neon, copper, gold and magnesium all have different physical and chemical properties. You can find descriptions of all of these elements on our Periodic Table of Elements.
The single most important difference between these elements is the number of protons each one contains in its nucleus. The number of protons an atom contains dictates how many electrons it will have. It is the arrangement of electrons around an atom's nucleus that determines that atom's chemical properties.