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bond angles

Posted: Thu Nov 14, 2019 11:56 pm
by 705379941
Why are angles "a little less than" certain angles?

Re: bond angles

Posted: Thu Nov 14, 2019 11:58 pm
by Daniel Martinez 1k
Some angles have "less than" because they have lone pairs, which distort the pull that the atoms have on each other.

Re: bond angles

Posted: Fri Nov 15, 2019 12:03 am
by Kelvin Chung 1C
Also, if the atoms bonded to the central atom are not the same atoms (e.g. CH2ClI) bond angles can differ due to differences in the different atoms' electronegativities.

Re: bond angles

Posted: Fri Nov 15, 2019 12:46 am
by William Chan 1D
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.

Re: bond angles

Posted: Fri Nov 15, 2019 12:55 am
by Shail Avasthi 2C
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.

Re: bond angles

Posted: Fri Nov 15, 2019 2:27 pm
by Letty Liu 2C
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?

Re: bond angles

Posted: Fri Nov 15, 2019 3:21 pm
by Emily Chirila 2E
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.

Re: bond angles

Posted: Fri Nov 15, 2019 3:28 pm
by Junxi Feng 3B
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.

Re: bond angles

Posted: Fri Nov 15, 2019 3:33 pm
by Julia Mazzucato 4D
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.

Re: bond angles

Posted: Fri Nov 15, 2019 6:12 pm
by Miriam Villarreal 1J
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.