What are Alkanes?
Alkanes are the simplest organic compounds, containing only carbon and hydrogen atoms joined by single bonds. They form the backbone of organic chemistry, found in natural gas, petroleum, and fuel.
Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂ (for straight-chain alkanes). Each carbon forms four single bonds, and there are no double or triple bonds.
- •Methane (CH₄): −162 °C
- •Ethane (C₂H₆): −89 °C
- •Propane (C₃H₈): −42 °C
- •Hexane (C₆H₁₄): 69 °C
- •Octane (C₈H₁₈): 126 °C
- •Dodecane (C₁₂H₂₆): 216 °C
Step-by-step worked examples
What is the molecular formula of pentane?
Pentane has 5 carbons (n=5). CₙH₂ₙ₊₂ = C₅H₁₂
A straight-chain alkane contains 8 carbons. How many hydrogens?
n = 8 H = 2(8) + 2 = 18 Formula: C₈H₁₈ (octane)
Is C₆H₁₄ a valid alkane formula?
Check: 2(6) + 2 = 14 ✓ Yes, this is hexane.
Flashcards
Quick quiz
Q1.General formula for alkanes?
Q2.How many bonds does each carbon in alkane have?
Q3.Methane (CH₄) is a…
Q4.Boiling point increases with chain length because…
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Common mistakes
Alkanes contain double bonds. — Correct: Alkanes contain only single C−C and C−H bonds.
All alkanes are liquids. — Correct: Small alkanes (CH₄, C₂H₆, C₃H₈) are gases; larger ones are liquids or solids.
Alkanes are very reactive. — Correct: Alkanes are relatively unreactive; they require heat or a catalyst for reactions.
The formula for pentane is C₅H₁₀. — Correct: Pentane is C₅H₁₂ (using CₙH₂ₙ₊₂).
FAQ
What is the structure of alkanes?
Alkanes are chains or branches of carbon atoms, each bonded to four other atoms (C or H) by single covalent bonds.
Why are alkanes hydrophobic?
Alkanes are nonpolar; they have no significant charge separation. They do not dissolve in polar solvents like water.
Are isomers possible in alkanes?
Yes. Branched isomers like isobutane (2-methylpropane) and n-butane have the same formula but different structures.
What is complete combustion of an alkane?
CₙH₂ₙ₊₂ + (3n+1)/2 O₂ → n CO₂ + (n+1) H₂O. It produces heat and is used for fuel.