Answer:
CH4 < CH3CH3 < CH3CH2CH3
Step-by-step explanation:
Alkanes are the simplest hydrocarbons (compounds of C and H), they have no functional group and the bonds between carbon atoms (with sp3 hybridization) are simple bonds, each orbital is directed to the vertices of a tetrahedron. Each orbital forms a σ bond with each H.
Alkanes may have a straight or branched chain. When the compounds have the same molecular form and only differ in the order in which the atoms in the molecule are linked, they are called constitutional or structural isomers.
The interaction between molecules (intermolecular forces) is a balance between the repulsion of the external electrons and the attraction of the nuclei of a molecule on the electrons of which they are close.
Alkanes without electronegative atoms have a relatively dense and continuous "shell" of electrons. The repulsion of electronic clouds is important and therefore the attraction between alkane molecules is very weak.
The "shape" of the molecules affects the contact surface. What do these experimental data suggest? Unbranched molecules, with linear zigzag structure, attract more effectively.
In other words, the longer the C chain in alkanes increases the intermolecular forces.