Two ball-and-stick representations of methane CH₄ (labelled (a) in the diagram) and bromomethane CH₃Br (labelled (b) in the diagram). Both diagrams have a central carbon atom (shown as a grey sphere). Methane then has 4 white spheres connected to it (the hydrogen atoms). Bromomethane has 3 white spheres (hydrogen) and one red sphere (representing bromine).