Both carbon and silicon belong to Group 14 of the periodic table and have a valency of 4, yet carbon shows extensive catenation while silicon does not. Explain the property of the carbon atom that accounts for this difference, and state what this means for the stability of C–C chains compared to Si–Si chains.
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Model Answer
Carbon's small atomic size allows its nucleus to hold shared electron pairs very strongly, making the C–C bond very strong and stable. This property, called catenation, allows carbon to form long, stable chains.
Silicon, though also tetravalent, has a larger atom, so Si–Si bonds are much weaker, making silicon hydride chains (up to 7–8 atoms) very reactive and unstable.
Source: Chapter 4, Section 4.2 – Versatile Nature of Carbon
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Explanation
- Examiners expect two key points: (1) small size → strong bond, and (2) contrast with silicon's weak/reactive chains.
- The term catenation must appear.
- Avoid over-explaining; two tight sentences covering both points earn full marks.
- "Strong bond = stable chain" is the core logic the examiner is looking for.