CorrectBond anglesThe types of electron groups not only affect the electron and molecular geometries but have differing effects on bond angles. Lone pairs of electrons repulse otherelectron groups more strongly than single bonds. For instance, four single bonds in a tetrahedral formation will yield 109.5bond angles because all bonds equallyrepulse each other. In the case of three single bonds and one lone pair (e.g., in, the electron geometry is tetrahedral, and the molecular geometry is trigonalpyramidal), the bond angle between the three single bonds will actually be more acute than the predicted 109.5(instead, they are 107.8) because the repulsion fromthe lone pair forces the bonds closer together.This behavior can also be seen in the simulation. Click theReal Moleculesmode, and selectas the molecule. Check the box markedShow Bond Angles, andswitch between theRealandModelradio buttons centered at the top of the simulation. What is being demonstrated is the increased repulsion of lone pairs, and that iswhy the model predicts 109.5, and the actual bond angle is 104.5. These differences in the bond angles can be seen for the following compounds in the simulation:,,,,, and. There are no changes to predicted bond angles when all the bonds are in the same plane because the lone pairs are equallyrepulsing on each side of the plane, which occurs in the case ofand.
