how do u know if a bond is polar or non polar??

I googled this question and i found out that if the elctronegativity is 0, it is pure covalent, if it is 0 to 0.5, it is covalrnt, if it is 0.5 to 1.7, it is polar bond and if it 1.7 and up, it is ionic bond.......i got this stuff as i am familiar with the ionic and covalent bonding, but the question remains the same, how do we know if it is polar r non polar? plz help me thnx

if one of the element is metal and other is non metal then it is ionic .However if the bonding is between non-metal and non metal then it either polar or non polar.
Non polar is bonding is in identical non-metals with no difference in electronegativies or due to symmetrical structure it has zero dipole moment.  for example --F2 or O2 ,CCl4 CH4 etc
polar compounds has the net dipole moment due to  bonding in elements of different electronegativies.
for example: HCl or NH3