What is an Atom?

 An atom is a little (tiny sounds better) unity of materia that is composed by particles, those particles may be of three different kinds: the first of them is the electron,  they have negative electric charge; one atom has a group of electrons surrounding it´s nucleus, and this nucleus is composed by the other two kind of atom particles: neutrons and protons, neutrons have neutral electric charge, protons, on the other hand, have positive electrical charge.