shape of molecules a level chem

do you look at lone pairs to work out electron geometry? is that why NH3 is tetrahedral (3 bonding pairs, 1 lone pair) rather than trigonal planar? then to see specifically molecular geometry you take into account how the number of lone pairs changes bond angle? i think this is right but im getting unclear explanations online when i search it up and my textbook is no help

you dont use lone pairs in deciding on the overall shape, but it is crucial to find them as they will affect bond angles. try here: https://www.science-revision.co.uk/A-level_shapes_finding_the_lonepair.html

you dont use lone pairs in deciding on the overall shape, but it is crucial to find them as they will affect bond angles. try here: https://www.science-revision.co.uk/A-level_shapes_finding_the_lonepair.html

This is incorrect? Lone pairs are very much involved in determining overall shape. 3 bonding pairs and 1 lone pair would give a trigonal pyramidal shape rather than a trigonal planar shape, for example.

Hi its not incorrect, the presence of lone pairs will affect bond angles, but in deciding on the overall shape of a molecule lone pairs are not taken into account. In the example you give it is the three bonding pairs that determines the shape of the molecule, not the lone pairs. Trigonal planar molecules have 6 valency electrons, trigonal pyramidal molecules have 8 valency electrons in the example you give, so based on a tetrahedral molecule, its not tetrahedral because you DONT take the lone pair into consideration when deciding on the overall shape. The molecules shape will be trigonal pyramidal as you said but the presence of the lone pair will compress down the bond angles you might expect as its based on a tetrahedral structure.