Bond Angles

[Quinton Sprague 1A]

I am reviewing what bond angles are associated with each VESPR structure and was curious why tetrahedral compounds have bond angles of 109.5 or less. Since linear, 180 x 2 = 360, trigonal planar, 120 x 3 = 180, but tetrahedral, 109.5 x 4 = 438??

[gabbi_r2C]

This is because tetrahedral compounds have atoms in different planes, so they will not add up to 360 or 180 degrees; the bond angles are 109.5 based on an experiment, but this is only because of the orientation of the atoms being 3D.

[Moura Girgis 1F]

A slightly smaller or larger bond angle, in this case 109.5 degrees, could be the result of lone paired electrons which take up more space than the usual bonds.

[KhanTran3K]

Hey!
I believe in one of the lectures, Dr. Lavelle talks about how the difference between these is that in the tetrahedral molecule, the atoms occupy more than one plane. With this, it can maximize the bond angles, since if it was all in one plane the angles would be 90 degrees. Also, adding on, the reason why it can be less than 109.5 is due to the possibility of lone pairs, since these lone pairs repulse the electrons of the bonded atoms more. Hope this helps!

[America Ramirez 3H]

as previously stated, it's because the tetrahedral shape takes up more than one plane so it doesn't have to stay in the 360-degree pattern.