This video shows how all atoms are made of protons, neutrons (in the nucleus) and electrons (outside the nucleus). The positive charge of the protons and the negative charge of the electrons create an attractive force that holds the atom together. The number of protons in the nucleus determines which element the atom is. For example, all carbon atoms have 6 protons in their nuclei. Because neutral atoms carry no overall charge, the number of protons and electrons must be equal, thus cancelling out their charges. Electrons are wrapped around the nucleus in shells, with definite rules governing how many electrons each shell can hold. When atoms collide with each other, their outer shells come into contact with each other, so the number of electrons in an atom’s outer shell is incredibly important. This number of electrons determines the properties of the atom.