Atomic Structure 1.9 understand that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shells

Protons, neutrons and electrons


As you can see from the diagram, in the centre of the atom is the nucleus, which contains protons (positive charge) and neutrons (no charge). Orbiting the nucleus is a series of shells, which hold electrons (negative charge). The electrons are much smaller than the protons and neutrons. 
The first shell outside the nucleus can hold 2 electrons, the second can hold 8 and the third can hold 8.