Atoms are the most basic unit of matter known. Every atom has electrons, a nucleus, neutrons, and protons. Protons, electrons, and neutrons have a positive, negative, and neutral charge respectively. 

All matter is made of atoms. Elements on the Periodic Table of Elements have an atomic number and atomic mass. The atomic number is the number of electrons and protons in stable atoms. The atomic mass is the weight of the stable. It is the sum of the number of protons and the number of neutrons. In other words, we can use the formula, atomic mass-atomic number=number of neutrons, to find the number of neutrons in an atom of an element. 

The types of atoms are isotopes, ions, and stable atoms. Isotopes are atoms of an element with different numbers of neutrons, but the same number of electrons and protons. Ions are atoms that have more or less than the normal number of electrons in a stable atom. An ion is considered to have a positive charge when it has a lesser number of electrons than it’s atomic number. An ion is considered negative when it has more electrons than its atomic number. Stable atoms are atoms that are balanced with the same number of electrons and protons and a correct number of neutrons. 

The concept of the atom was first discovered by Democritus, a Greek philosopher, and he believed that dividing a substance, again and again, would lead you to something that would be impossible to separate.