Here’s a summary of the physical properties of alkanes, which are the simplest hydrocarbons containing only single bonds (C–C and C–H):
1. State at Room Temperature
- C₁–C₄: gases (methane, ethane, propane, butane)
- C₅–C₁₇: liquids (pentane to heptadecane)
- C₁₈ and above: solids (waxes, paraffin)
2. Color and Odor
- Colorless and odorless in pure form
- Commercial alkanes may have slight smell (e.g., natural gas has odorant added for detection)
3. Solubility
- Insoluble in water (non-polar molecules, cannot form hydrogen bonds)
- Soluble in non-polar organic solvents (like benzene, ether, carbon tetrachloride)
4. Density
- Less dense than water (typical densities: 0.6–0.8 g/cm³)
- They float on water.
5. Boiling and Melting Points
- Increase with molecular weight (chain length) due to stronger van der Waals forces.
- Branched alkanes have lower boiling points than straight-chain isomers (less surface area → weaker van der Waals forces).
Examples:
- Methane (CH₄): –161°C
- Ethane (C₂H₆): –89°C
- Butane (C₄H₁₀): –1°C
- Octane (C₈H₁₈): 125–126°C
6. Melting Points
- Show an alternating pattern: even-numbered chains pack better → slightly higher melting points than odd-numbered chains of similar size.
7. Other Physical Traits
- Odorless, colorless, non-polar
- Low reactivity in physical interactions
- Flammable: readily combust in air producing CO₂ and H₂O
- Viscosity: increases with molecular weight
In short: alkanes are non-polar, hydrophobic, low-density, colorless, and mostly unreactive physically, with properties strongly dependent on chain length and branching.