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

Atoms are made up of protons, neutrons and electrons. The protons and neutrons from the nucleus, which is at the center of the atom and makes up most of its mass. Electrons orbit around the nucleus in shells, and are held to the atom by forces of attraction (kind of like a magnet) because the nucleus has a positive charge (clap clap protons) and the electrons have a negative charge (clap clap electrons)