To predict the shape of simple molecules we can use a simple procedure with 4 steps.

Step 1 Draw an electron dot diagram of all the bonds in the molecule.

Step 2 Identify the central atom.

Step 3 Count the number of bonding and non-bonding pairs of electrons around the central atom.

Step 4 Separate all the pairs of electrons surrounding the central atom as far apart from each other as possible. Don't forget we are working in 3 dimensional space.

Look at the animation on the left.