If the bond angles at a carbon atom are 120 degrees how many groups are around the carbon atom?

Question

I think 3 is the answer

Answer 1

If the bond angle is EXACTLY 120 degrees then there must be three identical atoms attached to the carbon in a trigonal planar arrangement.  Even if there are two of one kind of atom and different third atom, the bond angles will probably not be exactly 120 degrees, but close enough for government work.

If the bond angle is in the neighborhood of 120 degrees then there could be three bonds to three atoms, or there could be two bonds and 1 one lone pair.  With two bonds and one lone pair the bond angle will be less than 120 degrees because of the distortion caused by the delocalized, nonbonding pair of electrons.  The nonbonding electrons tend to "wrap" around the carbon and push the bonding pairs of electrons closer together, decreasing the bond angle.

Catbarf (what a name) brings up another issue, with two single bonds and a double bond, as in CH2O.  This type of arrangement will NEVER produce bond angles of exactly 120 degrees, but they will also be in the neighborhood of 120 degrees.  For instance, the H-C-H bond angle will be less than 120 and the two H-C-O bonds will be greater than 120 degrees.

Answer 2

If the bond angle is 120 degrees then the orbitals are in sp2 hybrid state, meaning that the ELECTRON PAIR geometry is trigonal planer. The three sp2 orbital around the carbon are oriented in the direction of an equilateral triangle and the angle between them is 60 degrees.

But, this has absolutely nothing to do with the number of groups attached to the carbon atom, there could be one or there could be a maximum of three.

If only one group is attached, then it is obviously linear, although when two atoms are attached to each other we do not really speak of molecular geometry.

If two are attached, and a lone pair then the molecular geometry is "bent" as the lone pair repels the bonding electron pairs and produces a "bent" geometry as dictated by the Valence Shell Electron Pair Repulsion, or VSEPR, model. An example of this type of geometry is Sulfur Dichloride, SCl2.

If all three orbital are bonding, then the molecular geometry is trigonal planer, such as boron trifluoride, BF3.

Remember, the ELECTRON PAIR geometry does not change, still remain trigonal planner in ALL three cases but the MOLECULAR geometry varies depending on the number of bonds.

Well, hope that help mate

Answer 3

You think right.  120 degree orientation occurs with sp2 molecular bonding, as noted with two single bonds to 2 groups and a double bond to the third.