Overview
This lecture explains the differences between ionic and covalent bonds, how to identify them, and the criteria for classifying bonds as ionic, polar covalent, or non-polar covalent.
Ionic Bonding
- Ionic bonding involves the transfer of electrons from one atom to another.
- Metals (like sodium) lose electrons to form positively charged ions (cations); non-metals (like chlorine) gain electrons to form negatively charged ions (anions).
- The resulting opposite charges attract, creating an electrostatic force known as the ionic bond.
- Ionic compounds typically form between metals and non-metals.
Covalent Bonding
- Covalent bonding involves the sharing of electrons between atoms.
- When two atoms share electrons equally, it forms a non-polar covalent bond; when shared unequally, it forms a polar covalent bond.
- Non-polar covalent bonds occur between identical non-metals (e.g., H₂, Cl₂).
- Polar covalent bonds occur when one atom is more electronegative, pulling shared electrons closer (e.g., H–F).
- Electronegativity is the ability of an atom to attract electrons toward itself.
Identifying Bond Types
- Ionic bonds typically occur between metals (left side of periodic table) and non-metals (right side).
- Non-polar covalent bonds occur between identical non-metals or those with an electronegativity difference less than 0.5.
- Polar covalent bonds occur between different non-metals with an electronegativity difference of 0.5 or greater.
- Hydrogen bonded to N, O, or F forms especially strong polar covalent bonds known as hydrogen bonds.
Practice Examples
- MgO: Ionic (metal + non-metal)
- Cl₂: Non-polar covalent (identical non-metals)
- NaF: Ionic (metal + non-metal)
- HBr: Polar covalent (electronegativity difference ≈ 0.7)
- IBr: Non-polar covalent (electronegativity difference ≈ 0.3)
- C–H: Non-polar covalent (difference ≈ 0.4)
- H–O: Polar covalent (difference = 1.4)
- F₂: Non-polar covalent (difference = 0)
- CaS: Ionic (metal + non-metal)
Key Terms & Definitions
- Ionic Bond — Bond formed by the transfer of electrons and electrostatic attraction between oppositely charged ions.
- Covalent Bond — Bond formed by sharing electrons between atoms.
- Polar Covalent Bond — Covalent bond with unequal sharing of electrons due to a difference in electronegativity ≥ 0.5.
- Non-polar Covalent Bond — Covalent bond with equal sharing of electrons, usually between identical atoms.
- Electronegativity — The tendency of an atom to attract shared electrons in a bond.
Action Items / Next Steps
- Use your textbook’s electronegativity table for homework problems.
- Practice classifying bonds (ionic, polar covalent, non-polar covalent) using provided examples.