(Polar molecules, Non-polar molecules, etc.)
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The bond angles depend on the existence of lone pairs because the lone pairs repel each other and other atoms in molecules. Bond angles decrease as the number of lone pairs increase. For example, in a tetrahedral shape, the bond angle would be 109.5 given that there are 4 atoms. If one of the atoms were replaced with a lone pair of electrons, the shape would become trigonal pyramidal and therefore the bond angle between the atoms would become less than 109.5 (~107) as a result of greater repulsion.
Just to add on, lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion. In the tetrahedral example mentioned by Kayla, the bond angle between the atoms in a trigonal pyramidal shape becomes less than 109.5 because the lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion. Hence, the atoms are forced closer together and the bond angle becomes slightly smaller.