Why Is Methane a Gas & Hexane a Liquid?


Methane exists as a gas and hexane in liquid form at room temperature because intermolecular forces affect the molecules of these substances differently.


  • When molecules of a substance stick together very firmly, it exists as a solid; when they stick somewhat firmly, the substance exists as a liquid; and when they barely attract each other at all, the substance becomes a gas. Intermolecular forces affect how molecules attract each other.

Types of Intermolecular Forces

  • Different forces affect different compounds. Common intermolecular forces, also called Van der Waals forces, include hydrogen bonding, dipole-dipole force, and London dispersion force or temporary dipole force.

London Dispersion Force

  • Hydrocarbons, such as methane and hexane, being nonpolar, only experience the London dispersion force--an effect that forms temporary poles in molecules, causing molecules to attract one another.


  • Since larger alkane molecules have more surface area, London dispersion force affects them more strongly and makes them group together in a more stable manner. This condition makes the boiling point of a larger alkane higher than that of a smaller alkane. Methane and hexane exemplify this trend.

Boiling Points

  • As Elmhurst College describes, methane boils at negative 164 degrees C (-263 degrees F) whereas hexane boils at 69 degrees C (156 degrees F.) This makes methane a gas and hexane a liquid at all normal temperatures on the Earth's surface.


  • Photo Credit Image by Flickr.com, courtesy of Conan
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