You seem to understand this concept. Continue with your reading. The following classification will help define the states in which matter can occur.
All matter is made up of chemical elements, each of which is made up of particles called atoms.
A rather crude, but useful, picture of an atom is that of a rigid sphere. There are 92 so-called naturally occurring elements of which 90 can be detected on Earth at this time. For our purposes we will ignore quarks and other particles that we would encounter if this were a upper level physics course. The atomic number is the number of protons in the nucleus of the atom. The atomic mass number is the number of protons plus neutrons in the nucleus.