The three parts of an atom are the protons, neutrons and electrons. Atoms make up the basic building blocks of matter and define the structure of elements. These parts were not officially identified until 1932.
Protons and neutrons are heavier than electrons, and this characteristic causes them to stay in the nucleus, while the electrons exist in a cloud around the nucleus. The cloud has a radius that is 10,000 times larger than the nucleus. The protons and neutrons normally have the same mass but can weigh more than 1,800 electrons. The number of protons, neutrons and electrons will differ from atom to atom. An atom of carbon will not have the same number of these parts as an oxygen atom. Normally, there are the same number of protons as neutrons giving the atom a neutral charge. When an elements neutrons begin to differ in number the atom becomes an isotope of the given element. Each element has a certain number of protons, which are used to give the element an atomic number. All the atoms of one element will have the same atomic number. The chemical symbol, mass number and more information for each element are listed on the periodic table. This table lists all the known base elements in the appropriate periods and groups.