Formulas, Functional Groups and the Naming of Organic Compounds

A hydrocarbon is a compound made up of carbon (C) and hydrogen (H) atoms only. Nothing else—just these two elements.

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)

• Ethanol (C₂H₅OH) contains oxygen, so it is NOT a hydrocarbon

Exam Tip: When defining hydrocarbon in an exam, you MUST include the word "only" — hydrocarbons contain carbon and hydrogen atoms only.

Alkanes are the simplest type of hydrocarbon. They have:

• Only single covalent bonds between carbon atoms
• No functional group (a functional group is a special atom or group of atoms that gives a molecule particular properties)

Because alkanes have no functional group, they are relatively unreactive compared to other organic compounds.

For straight-chain (non-cyclic) alkanes, the general formula is:

CₙH₂ₙ₊₂

where n = the number of carbon atoms

Example: If n = 3 (propane), then:

• Formula = C₃H₈ (which is 3 carbons and 2×3+2 = 8 hydrogens)

Alkanes can be:

• Linear (straight-chain): carbons arranged in a straight line
• Branched: the main chain has side branches
• Cyclic: carbons form a ring (e.g., cyclohexane, C₆H₁₂)