Lone Pairs

[Amanda Ung 4D]

Can someone elaborate/clarify what "lone pairs do not influence molecular shape but only atom positions are used to name the shape" means? I thought lone pairs did have some part in influencing molecular shape such as in see-saw or bent. I might be misinterpreting this statement.

[Kaitlyn Ang 1J]

Lone pairs do influence the bond angles and contribute to molecular shape (i.e. H2O is a bent shape instead of linear because of the 2 lone pairs) but when we are asked to find bond angles or draw dipole moments, we focus on the bonded atoms and not the lone pairs. And though we know that H2O has technically 4 "areas", we call it bent because only 2 of those "areas" (the areas that are bonded with other atoms) are being seen.

[Helen Struble 2F]

^^Lone pairs definitely influence molecular shape. Compared to shapes which do not have lone pairs, shapes with lone pairs usually have smaller bond angles because of the stronger repulsion. However, the actual name ("see-saw" or "trigonal pyramidal") comes from the geometric arrangement of the atoms, not the lone pairs. So while the lone pairs contribute to the geometry of the atoms, but ultimately the shapes are named for the geometry of the atoms.