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

A covalent bond is a bond between two atoms in which the electrons are shared relatively evenly. This occurs when the difference between the electronegativity values of the two atoms is less than 0.5.

Electronegativity values:

Periodic table with EN valuesPeriodic table with EN values

Perfectly covalent bonds (EN Difference = 0): 

Since a covalent bond is one where the electrons are shared relatively evenly because of similar electronegativity values, what would be the most covalent bond possible? It would have to be a bond between two identical elements, right? So compounds like H2 and Cl2 are as covalent as you can get.

Purely covalent bondsPurely covalent bonds

Nonpolar covalent bonds (EN Difference < 0.5):

So what happens when you’ve got a compound like methane (CH4)? Carbon’s electronegativity is value 2.5, and hydrogen’s is 2.2. That difference, 0.3, is still less than 0.5 so the bonds between carbon and hydrogen are considered covalent!

MethaneMethane

Polar Covalent Bonds (EN Difference between 0.6 - 1.9):

Hydrochloric acid is a great example of a polar bond. The difference between the two atoms’ electronegativity values is 1.0, so the bond between them would be considered polar.

Hydrochloric-acidHydrochloric acid

In a nutshell, if the difference in electronegativity values is between 0 and 0.5, the bond is nonpolar covalent; if it’s between 0.6 and 1.9, it’s polar covalent; anything greater than 2.0 is an ionic bond. Ionic bonds tend to have a very pronounced dipole, and the direction of that dipole is toward the more electronegative atom. Heads up: ionic compounds dissolved in polar media can conduct electricity pretty well!           

Reactivity:

Here’s a good rule of thumb in chemistry: the more evenly distributed the electron density, the less reactive the molecule is. You’ll often see bonds between nonmetals, like those in alkanes, that are unreactive in most conditions.

Examples:

Let’s go ahead and look at some molecules and see what type of bonds they have.

CO2­, N2Cl4, PH3, and PCl5 examplesCO, N2Cl4, PH3, and PCl5 examples


CO2-N2Cl4-PH3-and-PCl5-answersCO, N2Cl4, PH3, and PCl5 answers

In this post we’re only talking about bonds; we can use what we’ve learned here to explore the overall polarity of molecules in the Polar vs. Nonpolar post. Good luck studying!


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.