In high school chemistry, the Bohr atomic model is often used to describe how an atom works. Like all other models, it is a simplification of a much more complex system.
The atom has a nuclei which consists of protons and neutrons. Electrons orbit the nuclei in different electron shells.
The proton has a positive elementary charge, and the electron has a negative elementary charge. The neutron is uncharged.
There are as many protons as electrons in an atom. If there is a difference in the amount of protons and electrons, it is instead an ion of an atom.
The neutrons of the nuclei hold the positive protons together in the nuclei through strong nuclear forces, as they would otherwise repel each other due to their positive charge. The amount of neutrons within an atom with a certain amount of protons can vary, but in general there is approximately as many neutrons as there are protons in an atom. Read more about this in the article about isotopes.
The mass of protons, neutrons and electrons are described with the unified atomic mass unit (u). A proton has the mass 1.007 u, a neutron has the mass 1.009 u, and the electron has the mass 0.000549 u. A comparison between the particles of the atom can be seen in the table below:
The next article in the series is about electrons.