Master the art of naming alkanes and alkenes!
Hydrocarbons are molecules made entirely of carbon (C) and hydrogen (H) atoms. They're the building blocks of many things around you - from the petrol in cars to the plastic in your phone!
Carbon
Makes 4 bonds
Hydrogen
Makes 1 bond
This is super important: every carbon atom must always make exactly 4 bonds. This rule explains everything about hydrocarbon structures!
• In alkanes with single bonds (−), each bond counts as 1, so carbon needs 4 separate bonds
• In alkenes with a double bond (=), the double bond counts as 2 bonds, so that carbon only needs 2 more bonds to reach 4 total
That's why alkenes have fewer hydrogens! The double bond "uses up" two of carbon's four bonds, leaving room for fewer hydrogen atoms.
1. Alkanes (Single Bonds) - All bonds are single bonds (−). They end in -ane
2. Alkenes (Double Bonds) - Contains at least one double bond (=). They end in -ene
The smallest hydrocarbon is methane (CH₄) - it's the main component of natural gas and cow burps! 🐄💨
Alkanes are hydrocarbons with only single bonds between carbon atoms. They follow the formula: CnH2n+2
All alkane names end in -ane
| Number of Carbons | Prefix | Alkane Name | Formula |
|---|---|---|---|
| 1 | Meth- | Methane | CH₄ |
| 2 | Eth- | Ethane | C₂H₆ |
| 3 | Prop- | Propane | C₃H₈ |
| 4 | But- | Butane | C₄H₁₀ |
| 5 | Pent- | Pentane | C₅H₁₂ |
| 6 | Hex- | Hexane | C₆H₁₄ |
1 carbon atom with 4 hydrogens
2 carbons connected by a single bond
3 carbons in a chain - used in camping stoves! 🏕️
Monkeys Eat Peanut Butter Pretending Happiness
Meth-, Eth-, Prop-, But-, Pent-, Hex-
Alkenes are hydrocarbons with at least one double bond (C=C) between carbon atoms. They follow the formula: CnH2n
All alkene names end in -ene
| Number of Carbons | Prefix | Alkene Name | Formula |
|---|---|---|---|
| 2 | Eth- | Ethene | C₂H₄ |
| 3 | Prop- | Propene | C₃H₆ |
| 4 | But- | Butene | C₄H₈ |
| 5 | Pent- | Pentene | C₅H₁₀ |
| 6 | Hex- | Hexene | C₆H₁₂ |
You can't have an alkene with just 1 carbon (methene doesn't exist) because you need at least 2 carbons to make a double bond!
In the examples shown, the double bond is at the beginning of the carbon chain. However, the double bond doesn't have to be in that exact location! In larger alkenes, the double bond can be positioned between different carbon atoms in the chain. For example, but-1-ene has the double bond between carbons 1 and 2, while but-2-ene has it between carbons 2 and 3. Both are butene molecules, just with the double bond in different positions!
2 carbons with a double bond - used to make plastic bags! 🛍️
3 carbons with one double bond - used to make polypropylene!
4 carbons with one double bond
Ethene is a natural plant hormone! Fruits like bananas release ethene gas to help them ripen. That's why putting a banana in a bag with other fruit makes everything ripen faster! 🍌
Propane (alkane): C₃H₈ - All single bonds, more hydrogen atoms
Propene (alkene): C₃H₆ - Has a double bond, fewer hydrogen atoms
💡 Why fewer hydrogens? Remember: carbon always makes 4 bonds! In propene, the double bond uses up 2 of carbon's 4 bonds, so there's only room for 2 more bonds instead of 3. That's why each carbon in the double bond has fewer hydrogen atoms attached!
Number of Carbon Atoms
C₃H₈
3 carbons, all single bonds
All bonds are single bonds (−). Formula: CnH2n+2
Formula: C₄H₁₀