Chemistry · General Principles Of Organic Chemistry · NEET
Both carbon and silicon are tetravalent (4 bonds each), so at first they look equal. The difference is atomic size. Carbon is small, so a C-C bond is short and the shared electrons stay close to both nuclei, giving a strong bond (~348 kJ/mol). Silicon is bigger, so the Si-Si bond is longer and weaker (~226 kJ/mol) and easily attacked by water or oxygen. That is why carbon builds chains of thousands of atoms, while silicon chains stay very short.
No, but they work together. Tetravalence means carbon forms 4 bonds. Catenation means some of those bonds go to other carbon atoms, building a chain or ring. Tetravalence gives carbon the four 'hands'; catenation is what happens when carbon uses those hands to hold more carbon. A NEET question can test either idea, so keep them separate in your notes.
Carbon shows the maximum catenation of all elements. Going down Group 14 the tendency falls sharply: Carbon much greater than Silicon greater than Germanium greater than Tin, and lead shows almost none. The reason is that bond strength drops as atomic size increases down the group, so the self-linked chain becomes weaker and breaks easily.
Because carbon atoms are smaller. In a short C-C bond the bonding electron pair is pulled strongly by both small nuclei, so the bond has high enthalpy (~348 kJ/mol). In Si-Si the atoms are large, the bond is long, the electrons are far from the nuclei, and the bond is weak (~226 kJ/mol). Strong bonds resist breaking, so carbon chains survive and silicon chains do not.
Atomic size is the main reason, but there are two supporting points. First, the C-C bond enthalpy is high, so the chain is thermodynamically stable. Second, carbon can also form multiple bonds (C=C, C triple bond C) with itself, so catenation includes double and triple bonds, not just single bonds. Nitrogen and oxygen can self-link a little, but their lone pairs repel and make those chains unstable, so carbon still wins.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Catenation is the self-linking of atoms of the same element to form chains, branches, or rings. Carbon is the best example, forming chains of thousands of carbon atoms, which is why millions of organic compounds exist.
Carbon is a small atom, so its C-C single bond is short and strong (~348 kJ/mol). Strong bonds do not break easily, so long stable carbon chains form. Carbon can also self-link through double and triple bonds.
It decreases: C much greater than Si greater than Ge greater than Sn, and Pb shows almost none. As atomic size increases down the group, the bond between like atoms becomes longer and weaker, so the tendency to form chains falls.
Yes. Carbon can self-link with single (C-C), double (C=C), and triple (C triple bond C) bonds. This ability to form multiple bonds with itself adds to the huge number of possible organic structures.
NEET rarely asks catenation as a stand-alone question, but it is the base idea behind tetravalence, chain and position isomerism, and the huge number of organic compounds. Understanding it makes the rest of organic chemistry easier.
