Chemistry · Chemical Bonding · NEET
Look at the bond between the two carbons. A single bond (C-C, as in ethane) means each carbon is sp3. A double bond (C=C, as in ethene) means each carbon is sp2. A triple bond (C#C, as in ethyne) means each carbon is sp. Quick rule: single->sp3, double->sp2, triple->sp. This works because more pi bonds need more p orbitals kept free, so fewer orbitals mix.
Ethane: 1 sigma bond only. Ethene: 1 sigma + 1 pi bond (that is the double bond). Ethyne: 1 sigma + 2 pi bonds (that is the triple bond). A single line is always 1 sigma. Every extra line (double or triple) adds pi bonds. So a double bond = 1 sigma + 1 pi, a triple bond = 1 sigma + 2 pi.
Each carbon in ethyne makes a triple bond. A triple bond has 2 pi bonds, and pi bonds are made from unhybridised p orbitals. So carbon must keep TWO p orbitals free (unmixed) for the two pi bonds. That leaves only one s and one p orbital to mix, giving 2 sp hybrid orbitals. That is why ethyne carbon is sp, not sp3.
Ethane: about 109.5 degrees (tetrahedral, sp3). Ethene: about 120 degrees (planar, trigonal, sp2). Ethyne: 180 degrees (linear, sp). More s-character makes the molecule flatter and more open. sp3 has 25% s, sp2 has ~33% s, sp has 50% s. Higher s-character -> larger bond angle.
More pi bonds pull the carbons closer, and more s-character makes the sp orbital smaller and held nearer the nucleus. Ethyne (triple bond, sp) has the shortest C-C bond (~120 pm), ethene (double bond, sp2) is middle (~134 pm), and ethane (single bond, sp3) is longest (~154 pm). Rule for NEET: triple < double < single in bond length.
Yes. A single pi bond is weaker than a sigma bond because pi overlap is sideways and less effective than the head-on overlap of sigma. But a triple bond is stronger in TOTAL because it has 1 sigma + 2 pi bonds added together. Do not confuse total bond strength with the strength of one individual pi bond.
Match List-I with List-II. List-I (Molecule): A. ethane; B. ethene; C. carbon molecule C2; D. ethyne. List-II (bonds between the two carbon atoms): I. one sigma and two pi bonds; II. two pi bonds; III. one sigma bond; IV. one sigma and one pi bond.
Which of the following molecules represents the order of hybridisation sp2, sp2, sp, sp from left to right atoms?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Ethane is sp3, ethene is sp2 and ethyne is sp. The rule: single bond gives sp3, double bond gives sp2 and triple bond gives sp.
Ethyne (C2H2) has 3 sigma bonds in total (one C-C and two C-H) and 2 pi bonds. Between the two carbons alone there is 1 sigma + 2 pi.
Ethyne has the largest bond angle at 180 degrees (linear). Ethene is 120 degrees and ethane is about 109.5 degrees. More s-character means a larger angle.
Ethyne has a triple bond with more s-character (sp) and two pi bonds that pull the carbons closer, so its C-C bond (~120 pm) is much shorter than ethane's single bond (~154 pm).
NEET regularly asks you to match molecules to their hybridisation, or to count sigma and pi bonds. Ethane, ethene and ethyne are the model examples for sp3, sp2 and sp, so mastering them lets you solve many bonding questions fast.
