Lesson 1 of 13 · 10 min
Carbon's tetravalence and the shapes of organic molecules
NCERT § "Tetravalence of Carbon: Shapes of Organic Compounds"
Acetic acid has only two carbon atoms, yet they are not alike. One sits at the centre of a tetrahedron; the other lies flat in a plane. Same element, same molecule, two different shapes.
The lesson in notes
In short
Carbon is tetravalent and forms covalent bonds using hybrid orbitals: sp³ (tetrahedral, as in CH₄), sp² (trigonal planar, as in C₂H₄) and sp (linear, as in C₂H₂).
s character is 25% in sp³, 33% in sp² and 50% in sp; more s character holds electrons closer to the nucleus.
An sp-hybridised carbon is therefore more electronegative than sp², which is more electronegative than sp³.
More s character also means shorter and stronger bonds formed by that carbon.
A π bond forms by sideways overlap of unhybridised p orbitals; the two atoms joined by it and the atoms attached to them must lie in one plane, and rotation about the double bond is restricted.
π electrons lie above and below the bond axis and are loosely held, so multiple bonds are reactive centres attacked by electron-seeking reagents.
Simulations in this lesson
Each on its own page