(Polar molecules, Non-polar molecules, etc.)
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When an atom has lone pairs of electrons, the bond angles are often written with a "less-than" symbol because lone electron pairs have a slightly higher repulsion than normal bonding pairs do, so they push them away more lone pairs, and thus a little closer to other bonding pairs.
Lone pairs have greater repulsion strength than bonding regions do. So lone pairs will tend to push bonding regions closer together, making the bond angles "a little less then" their typical value. For example, if you have a tetrahedral with 1 lone pair, the three bonding regions will have bond angles of a little less than 109.5 because the lone pair is pushing them together more than another bonding region would.
Besides for some tetrahedral and trigonal pyramidal bond angles being less than 109.5, are there other molecular shapes we should know for test 2? Also, how would we know the bond angles for more complicated shapes like trigonal bipyramidals?
Letty Liu 1K wrote:Besides for some tetrahedral and trigonal pyramidal bond angles being less than 109.5, are there other molecular shapes we should know for test 2? Also, how would we know the bond angles for more complicated shapes like trigonal bipyramidals?
So far we're suppose to know: linear, trigonal pyramidal, tetrahedral, trigonal bipyramidal, octahedral, bent, and seesaw.
More complicated shapes usually have multiple possible bond angles. I would just try to visualize it and relate each angle to ones in the simpler molecular shapes.
There can be multiple reasons for this. One, for example, is due to the presence of lone pairs that repel electrons from other atoms, making the bond angles lower. Two, it can be the number of electrons on an atom: like the examples in class today-- SO3 2- and NH3. Since O has more electrons than H, it will be repelled further away that H, making the bond angle between SO3 2- slightly lower than NH3.
Differences in bond angles are dependent on the type of atoms involved in the molecule and their electronegativity and the lone pairs. For example, NH3 and SO32- are both AX3E molecules, but the NH3 has a 107 degree bond angle and SO32- has 106 degree bond angle.
Bonding pairs are slightly farther away from the central atom compared to lone pairs which utilize their higher repulsion to push the bonding pairs close together , taking up more space since they tend to be closer to the nucleus.
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