Alkanes
Alkanes are saturated hydrocarbons with single bonds.
About this topic
Alkanes are saturated hydrocarbons with only single bonds and the general formula CnH2n+2: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), pentane (C5H12). Carbon atoms are tetrahedral, with bond angles of about 109.5 degrees. They are named with the ending -ane.
Alkanes are nonpolar, so they are insoluble in water, and their only intermolecular forces are dispersion forces, which grow with chain length. Therefore the boiling point rises with size: methane to butane are gases, pentane to about C16 are liquids, and larger ones are waxy solids. Branched isomers have lower boiling points than straight chains because they pack less closely. They are fairly unreactive but burn readily, and react with halogens in sunlight by substitution: CH4 + Cl2 gives CH3Cl + HCl.
Worked example: octane, C8H18, in petrol burns as 2C8H18 + 25O2 gives 16CO2 + 18H2O. Natural gas, camping gas, petrol, diesel, candle wax and asphalt are alkane mixtures. Cycloalkanes form rings and have the formula CnH2n.
Misconceptions: that saturated means filled with something; it means maximum hydrogen atoms. Another is that all alkanes are gases. Also, alkanes are not all equally reactive in every condition, though they are generally resistant to acids and bases.
Key ideas
- CₙH₂ₙ₊₂
- Methane, ethane, propane
- Fuels
Quick check
Use cases: where Alkanes helps
- Homework: review the key idea behind Alkanes before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Alkanes without notes.
- Visual learning: play with the interactive lab to see how Alkanes changes when you adjust its inputs.
- Teaching a friend: explain Alkanes in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Alkanes?
Alkanes are saturated hydrocarbons with single bonds.
What will I learn in Alkanes?
CₙH₂ₙ₊₂. Methane, ethane, propane. Fuels.
Is Alkanes part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Alkanes lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Alkanes?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
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