Overview
This lecture explains the different types of chemical bonds—ionic, covalent (polar and nonpolar)—and how differences in electronegativity determine the bond type between atoms.
Types of Chemical Bonds
- Atoms in a molecule are held together by chemical bonds.
- The type of bond depends on the electronegativity difference between the two atoms involved.
Ionic Bonds
- Form when the electronegativity difference is greater than about 2.
- One atom (e.g., chlorine) takes an electron from another atom (e.g., sodium).
- Forms positive (cation) and negative (anion) ions.
- Ions attract each other due to opposite charges, creating a strong ionic bond.
- Electrons are transferred, not shared.
Covalent Bonds
- Occur when the electronegativity difference is less than about 1.7.
- Atoms share a pair of electrons rather than transferring them.
Polar Covalent Bonds
- Electronegativity difference is between approximately 0.5 and 1.7.
- Electrons are shared unequally; the more electronegative atom attracts electrons more strongly.
- The more electronegative atom becomes partially negative (δ–), the less electronegative atom becomes partially positive (δ+).
Nonpolar Covalent Bonds
- Electronegativity difference is less than 0.5.
- Electrons are shared evenly between atoms.
- No partial charges form; atoms may even be identical.
Predicting Bond Type
- Compare the electronegativities of two atoms to determine bond type:
- Difference < 0.5: Nonpolar covalent bond (electrons shared evenly).
- Difference 0.5–1.7: Polar covalent bond (electrons shared unequally).
- Difference > 2: Ionic bond (electrons transferred).
Key Terms & Definitions
- Electronegativity — the ability of an atom to attract electrons in a chemical bond.
- Ionic bond — a bond formed by the transfer of electrons from one atom to another, resulting in ions.
- Covalent bond — a bond formed when two atoms share electrons.
- Polar covalent bond — a covalent bond with unequal sharing of electrons, causing partial charges.
- Nonpolar covalent bond — a covalent bond with equal sharing of electrons and no charge separation.
- Anion — a negatively charged ion.
- Cation — a positively charged ion.
- δ– (delta minus) — symbol for a partial negative charge.
- δ+ (delta plus) — symbol for a partial positive charge.
Action Items / Next Steps
- Practice identifying bond types by comparing electronegativity differences between given elements.