All the matter which we can see with our eyes, called baryonic, it’s formed by atoms.
But what are the atoms?
The atoms, predicted for the first time in the XIX century by John Dalton, form, in big quantities, all we can see. The atoms can group into heavier elements. For example, the water is formed by two atoms of hydrogen and one atom of oxygen. There are a lot more elements that are formed by more atoms, for example the iron. Although, there are elements formed by a lot less atoms, like hydrogen. In the periodic table are classified all the elements that we know nowadays. All the elements are formed by atoms, which each of them has a different atomic number. The atomic number does reference to the number of protons of the nucleus of the atom, which is the same at the number of electrons that orbit the nucleus.
All the atoms are organized all in the same way. In the centre of the atom, there is its nucleus. The nucleus is compost by protons and neutrons. The protons and neutrons, which have an opposite electric charge, get maintain themselves attached due to the strong nuclear force, which maintain united the nucleus of the atoms. The protons are formed by quarks and gluons. In the protons there are, in total, three quarks: two quarks “up” and one quark “down”. In the neutrons happens the opposite: there are two quarks “down” and one quark “up”. The gluons, the other subatomic particle that forms part of the protons and neutrons, maintain united the quarks so that they don’t escape.
Around the nucleus of the atom there are the electrons. The electrons orbit the nucleus, and depending on the type of atom, there is more or less electrons. The electrons orbit the atomic nucleus in different capes, like an onion. There are the electrons that orbit very close to the nucleus and other that orbit the nucleus very separately.
The thing that determines the type of atom we find ourselves on (hydrogen, helium, oxygen etc.), is the number of protons, neutrons and electrons that he have.