How can the polarity of a covalent bond be determined?
1 Answer
The polarity of a covalent bond can be determined by determining the difference in electronegativity (
The difference in electronegativities (
 If the ΔEN is less than 0.5, then the bond is nonpolar covalent.
 If the ΔEN is between 0.5 and 1.6 (some use 1.7), the bond is considered polar covalent
 If the ΔEN is greater than 2.0, then the bond is ionic.
 If the ΔEN is between 1.6 and 2.0, and a metal is involved, then the bond is considered ionic. If only nonmetals are involved, the bond is considered polar covalent.
*Note that absolute values are used; there are no negative differences in electronegativity.
**A note about Rule 4: Some websites and textbooks consider a
(Source: http://www.chemteam.info/Bonding/ElectronegBondPolarity.html)
Example
Determine the

silicon (Si) and phosphorus (P): EN of Si = 1.90, EN of P = 2.19
#Delta"EN"# = 1.90  2.19 = 0.29, therefore the bond is nonpolar covalent. 
carbon (C) and oxygen (O): EN of C = 2.55, EN of O = 3.44
#Delta"EN"# = 2.55  3.44 = 0.89, therefore the bond is polar covalent. 
sodium (Na) and chlorine (Cl): EN of Na = 0.93, EN of Cl = 3.16
#Delta"EN"# = 0.93  3.16 = 2.23, therefore the bond is ionic.