Chemistry · General Principles Of Organic Chemistry · NEET
Count the number of sigma bonds (single bonds and one sigma from each multiple bond) plus lone pairs on that carbon. For carbon this equals the number of attached atoms plus lone pairs. 4 attached groups means sp3, 3 groups means sp2, 2 groups means sp. A double or triple bond still connects to only ONE other atom, so it counts as one group, not two. This shortcut works for almost every NEET carbon.
The four sp3 hybrid orbitals repel each other and spread out as far apart as possible in 3D space. The angle that keeps four electron pairs farthest apart in a tetrahedron is 109.5 degrees, not 90. If the orbitals were plain p orbitals they would be 90 degrees, but hybridisation mixes s and p character so the angle opens up to 109.5. This is why methane (CH4) is tetrahedral.
One group. Both electron pairs of a double bond point toward the SAME neighbouring atom, so they occupy one direction only. In ethene (CH2=CH2) each carbon touches 3 atoms (2 H and 1 C), so it is sp2 and trigonal planar. Counting the double bond as two would wrongly give you a different shape. Always count attached ATOMS, not bonds.
Linear, 180 degrees, sp hybridised. In ethyne (HC triple bond CH) each carbon touches only 2 atoms (1 H and 1 C), so it uses sp hybridisation and the two sigma bonds sit in a straight line. Any carbon in a triple bond, or a carbon with two double bonds like in CO2 or allene central carbon, is sp and linear.
An s orbital is spherical and holds electrons closer and more symmetrically. More s character in a hybrid orbital pulls the shape toward a wider, more open angle. sp has 50 percent s (180 degrees), sp2 has 33 percent s (120 degrees), sp3 has 25 percent s (109.5 degrees). So as s character rises, the bond angle rises: sp3 less than sp2 less than sp. This trend is a favourite NEET fact.
In which of the following molecules is the order of hybridisation sp2, sp2, sp, sp for the carbon atoms from left to right?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The hybridisation of each carbon decides its shape. sp3 is tetrahedral (109.5 degrees), sp2 is trigonal planar (120 degrees), and sp is linear (180 degrees). For the whole molecule, look at each carbon separately.
Methane (CH4) is tetrahedral. Its carbon is sp3 with four single bonds pointing to the corners of a tetrahedron at 109.5 degrees, not a flat square.
Ethyne (HC#CH) has sp carbons and a bond angle of 180 degrees, making the molecule linear.
sp hybridised carbon has the shortest and strongest C-H bond because it has the most s character (50 percent), pulling bonding electrons closer to the nucleus.
Yes. In propene (CH3-CH=CH2) the CH3 carbon is sp3 while the two carbons of the double bond are sp2. Always analyse each carbon on its own.
