Question about Molecules being Planar

[bruinguy083]

what exactly does planar mean? sp2 hybridization at all carbons? how is BF3 a planar molecule but NH3 is not? TIA

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[TheWiredNerv]

N: 5 e-
3 of those electrons go into bonds with the 3 Hydrogens. You have a lone pair of 2 electrons left. This creates 3 areas of electron density thus sp2.

B has 3 e- which form bonds with F. This is why BF3 is a lewis acid because it wants to accept an electron pair to have an octet.

 

[bruinguy083]

so what does being planar mean? sorry, still a bit confused.

 

[TheWiredNerv]

The three electron domains assume a triangle to minimize electron repulsions.
It is a triangle because 120 degrees represents the most stable configuration for any 3 points in space.

 

[red88m]

NH3 is sp3 hybridized, trigonal pyramidal.
BF3 is sp2 hybridized, trigonal planar.
Planar means that all the electrons in the atom are on one plane- if you had a molecular model of the molecule and laid it on the table, no parts would be sticking up in the air. It would all rest on the table. In NH3, the lone pair sticks up in the air and makes it pyramidal.
Tell me if I'm wrong here, somebody.