How can you tell if a molecule is polar or nonpolar

[ilii]

Hello,

for octane (C8H18), how can you tell whether or not it is polar or non-polar without drawing a lewis structure diagram? also, if you absolutely need to draw one, what is the easiest way to go about drawing a more advanced molecule like octane? I can draw simple molecules and find their shapes, i.e. planar triangles, etc, but I get lost when faced with bigger ones.

thank you

 

[Borek]

Alkanes are non-polar almost by definition.