Key Concepts
- 1What are hydrocarbons?
- 2What is a homologous series?
Important Formulas & Facts
Compounds of carbon and hydrogen only. Saturated (alkanes, single bonds: CₙH₂ₙ₊₂) and Unsaturated (alkenes C=C, alkynes C≡C). Methane CH₄ is simplest.
Series of compounds with same functional group, similar properties, and a common difference of -CH₂- (14 amu). Example: Methanol→Ethanol→Propanol (CH₃OH, C₂H₅OH, C₃H₇OH).
Must-Know Questions
Q1Carbon forms covalent bonds because:
Carbon has 4 valence electrons and needs 4 more to complete its octet. It can neither lose 4 electrons (requires too much energy) nor gain 4 electrons (nucleus cannot hold). So it shares electrons, forming 4 covalent bonds. This ability to form 4 bonds leads to the vast number of carbon compounds.
Q2What is the unique property of carbon that leads to formation of a large number of compounds?
The two unique properties of carbon are: 1. Catenation: The ability of carbon atoms to form bonds with other carbon atoms, forming long chains, branched chains, and rings. This is due to the strong C–C bond (bond energy 346 kJ/mol). 2. Tetravalency: Carbon has a valency of 4 and can form bonds with four other atoms of carbon or with atoms of other elements like H, O, N, S, Cl, etc. This gives rise to a very large number of compounds.
Q3What is the general formula for alkanes?
Alkanes are saturated hydrocarbons with single bonds only. General formula: CₙH₂ₙ₊₂. Examples: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀). They undergo substitution reactions.
Q4What are homologous series? Give an example.
A homologous series is a group of organic compounds having a similar structure and similar chemical properties, in which successive members differ by a CH₂ group (14 u in molecular mass). Characteristics: (1) Same general formula. (2) Same functional group. (3) Similar chemical properties. (4) Gradation in physical properties. Example: Alkane series — CH₄, C₂H₆, C₃H₈, C₄H₁₀... (general formula CₙH₂ₙ₊₂). Each successive member differs by -CH₂-.
Q5Write the IUPAC name of CH₃CH₂OH.
CH₃CH₂OH is ethanol (IUPAC name). It has 2 carbon atoms (eth-) with an -OH (hydroxyl) functional group (-ol suffix). Common name: ethyl alcohol. It is the alcohol present in alcoholic beverages.
Practice Carbon and its Compounds
Reinforce what you just revised with practice questions