Ch. 1 - A Review of General ChemistryWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Johnny Betancourt

Polar bonds, also called polar covalent bonds, are bonds between two atoms with a difference of electronegativity values greater than 0.5 and less than 2.0. In a polar bond, the electrons are unequally shared between the two atoms.

Electronegativity values: 

Periodic table with EN valuesPeriodic table with EN values 

Dipole Moment

When atoms have different electronegativity values, electrons are pulled toward the atom that is more electronegative. This causes partial charges to develop. Let’s take a look at good ol’ H2O. According to the periodic table above, oxygen’s EN (electronegativity) value is 3.5 and hydrogen’s is 2.2.

Water dipoleWater dipole

Polar vs covalent vs ionic bonds

When looking at bonds between atoms, knowing the type of bond is often useful. The best way to do that is to look at the difference between the EN values like we did with water above. If the difference between the EN values is less than 0.5, it's a covalent bond; if it's between 0.6 and 1.9, it's considered polar covalent; if it's above 2.0 it's an ionic bond. 

Here’s a good rule of thumb in chemistry: the more/unevenly distributed the electron density, the more reactive the molecule is. You’ll often see that polar molecules are susceptible to reactions like acid-base, substitution, and addition. Polarity is responsible for a ton of different effects like solubility, boiling point, melting point, and hydrogen bonding.

Examples:

Acetone, chlorine, chlorine monofluoride, trimethylamine, propylphosphine, and chlorine monobromideAcetone, chlorine, chlorine monofluoride, trimethylamine, propylphosphine, and chlorine monobromide

Go ahead and figure out if these molecules have polar bonds in them using the electronegativity values from the chart above. Be sure to indicate the partial charges and the direction of the dipole if the electronegativity values have a difference 0.5 or greater!

Molecules labeled polar or covalentMolecules labeled polar or covalent

Hope that helped! Check out my other posts on covalent bonds and polar vs. nonpolar molecules for more on this topic.




Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.