Here's why:
* Low molecular weight: These alkanes have very low molecular weights, which means they have weak intermolecular forces (van der Waals forces).
* Weak intermolecular forces: Weak intermolecular forces make it easier for the molecules to move freely and exist as gases.
As the number of carbon atoms in the alkane chain increases, the molecular weight increases and the intermolecular forces become stronger. This leads to the heavier alkanes being liquids (like propane and butane) or even solids (like pentane and higher) at room temperature.
