Why are alkenes nonpolar?
The alkenes are made of Carbons and Hydrogens with some double bonds between the Carbons that have little difference in electronegativity.
Non polar molecules are made of atoms that have small differences in electronegativity.
Carbon has an electronegativity of 2.5 while Hydrogen has an electronegativity of 2.2. This is a difference of only .3 electronegativity. This makes the compound non polar.
Polar covalent molecules like water have a greater difference of electronegativity.