Tetrahedral Angles

(Polar molecules, Non-polar molecules, etc.)

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Amber_Candelaria_1D
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

Tetrahedral Angles

Postby Amber_Candelaria_1D » Mon Oct 31, 2016 9:58 am

Hi, I've memorized the bond angles for all the VSEPR geometries but I don't seem to understand why the tetrahedral shape has angles of 109.5 degrees. It's hard for me to picture it without a 3D diagram. Could anyone explain? Thank you in advance!

Eljie_2F
Posts: 19
Joined: Fri Jun 17, 2016 11:28 am

Re: Tetrahedral Angles

Postby Eljie_2F » Mon Oct 31, 2016 10:31 am

Hi Amber,

When looking at an atom in 2D as if all atoms are circles, it is clear that the largest angle 4 atoms around 1 central atom can get is 90 degrees. But in reality, these atoms are spherical in shape, and this results in more space for the atoms to spread out. If all 4 atoms were spread out along the equator of a sphere, it can be seen that there is empty space above and below the equator. In this incorrect model, each atom has 90 degree angles between itself and the atoms to its right and left. It also has an 180 degree angle in relation the atom on the completely opposite side of the sphere. Since these atoms repel each other, they will naturally be dissatisfied with having two 90 degree angles and will spread out evenly towards the empty space above and below the equator of the sphere. Thus the atoms will reach an angle of 109.5 degrees, an angle that is between the 90 and 180 degree angles that occur when the atoms surround the central atom using only two dimensions of space.


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