When is nonpolar covalent bond formed?

Answer 1

When two elements of similar electronegativities bond together, simply subtract the smaller electronegativity from the larger one, you will see different values, but I usuallly go with any difference less than .4 to be nonpolar.

However even most nonpolar bonds exhibit a "net dipole moment." This is a product of the random nature in which electrons orbit the nucleus, this leaves some sections of a molecule with electrostatic "hot spots" of momentarily (about a femtosecond) charged areas, whereas these dipole interactions (a subset of the Van der Walls interactions) are incredibly weak in respect to the four fundamental forces and are very short-lived the cumulative force of these bonds attributes to many phenomenon most notably water's nature as a "universal solvent" but this is a very lengthy discussion of a simple question so anyone interested in knowing more can message me.