(Polar molecules, Non-polar molecules, etc.)
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So when determining the molecular shape, lone pairs are considered a region of electron density but they don't make it the shape associated with that number of e- density regions correct? For example NH3 has 4 regions of electron density, one of which being a lone pair, but that doesn't make the shape tetrahedral but trigonal pyramidal?
That is exactly correct. The lone pairs influence the overall shape and account for a region of electron density but not directly so that four regions, including one lone pair, would not yield tetrahedral. This only occurs with 4 bonds.
To add on, the lone pairs will push away from the bonds stronger, making bond angles smaller. Thus, looking at the VSEPR formula is extremely helpful when determining shape. For example, AX3 will yield trigonal planar with bond angles 109.5 but AX3E will yield trigonal pyramidal with bond angles <109.5. The lone pair pushed the bonds closer together.
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