Why is bond angle 109.5

Basic VSEPR theory is not intended to be quantitative, and cannot be used to predict precise bond angles. An exception is when all bond angles are equal square planar, tetrahedral , etc. Related terms: Bond length , strain , steric strain , torsional strain , angle strain , ring strain , wedge.

VSEPR theory predicts a linear structure for carbon dioxide instead of a bent structure because a linear structure places the four bonding electrons pairs two pairs in each double bond as far apart as possible. Each orbital is equivalent and oriented at the corners of a tetrahedron. One can think of a sp 3 hybrid orbital as having However, it is not necessary for each of the hybrid orbitals to be equivalent or that the s and p orbitals need be combined in integer proportions.

Recall that hybrid orbitals are just mathematical functions constructed from the the basic mathematical functions that are the atomic s and p orbitals.

But for NH 3 , the hybrid orbital accommodating the lone pair might be expected to have a different composition than the hybrid orbitals associated with the N-H bonds. As the formulation of the hybrid orbitals differ from sp 3 , the geometries of the orbitals differ from tetrahedral. The hybrid orbitals are constructed from the NBO formalism. For NH 3 , the hybrid orbitals for both the bonding pairs and lone pairs are each very close to sp 3 , which predicts a trigonal pyramidal geometry with Note, though, that the nitrogen lone pair has slightly more s character and slightly less p character than the sigma bonding orbitals, consistent with the lone pair occuping more space than a sigma bonding pair.

And we've seen in an earlier video that this carbon is sp3 hybridized, which means that the atoms around that central carbon atom are arranged in a tetrahedral geometry. It's very difficult to see tetrahedral geometry on a two-dimensional Lewis dot structure. So it's much easier to see it over here on the right with the three-dimensional representation of the methane molecule.

So if I'm trying to see the four sides of the tetrahedron, I could find my first sides by connecting these hydrogen atoms like that. So there's the first side of my tetrahedron.

And if I'm going to find the second side, I could connect these hydrogen atoms like that. And there's my second side.

And to find my last two sides, if I connect this hydrogen atom to this one down here, I can now see the four sides of my tetrahedron.

We're also concerned with the bond angle. So what is the bond angle? What is the angle between that top hydrogen, the essential carbon, and this hydrogen over here on the left? It turns out that bond angle is And it's the same all the way around. So you could say that this angle is It's all the same. And so an sp3 bond angle is And the proof for this was shown to me by two of my students.

So Anthony Grebe and Andrew Foster came up with a very nice proof to show that the bond angle of an sp3 hybridized carbon is And what they did was they said let's go ahead and take that tetrahedron, and let's go ahead and put it on the xyz axes. And let's put carbon at the center here.