Overview
This lesson explains the differences between ionic, polar covalent, and nonpolar covalent bonds, focusing on examples and the role of electronegativity.
Types of Chemical Bonds
- Ionic bonds form between metals and nonmetals, involving transfer of electrons.
- Covalent bonds form between nonmetals and involve sharing electrons.
- Nonpolar covalent bonds occur when electrons are shared equally.
- Polar covalent bonds occur when electrons are shared unequally due to electronegativity differences.
Nonpolar Covalent Bonds
- Bonds between identical atoms (e.g., H–H, C–C) are always nonpolar covalent.
- Electrons in nonpolar covalent bonds are shared equally.
- Carbon-hydrogen (C–H) bonds are nonpolar covalent due to a small electronegativity difference (0.4).
Polar Covalent Bonds
- Bonds between different nonmetals with an electronegativity difference ≥ 0.5 are polar covalent.
- In a C–O bond, the difference is 1.0, making it polar covalent.
- Oxygen is more electronegative than carbon, so it acquires a partial negative charge.
- The polarity of a bond is indicated by an arrow pointing toward the more electronegative atom.
- O–H bonds are highly polar (difference: 1.4) and participate in hydrogen bonding if H is bonded to N, O, or F.
Ionic Bonds
- Formed by transfer of electrons when a metal bonds with a nonmetal (e.g., Na–Cl, Li–F).
- Metal becomes a positively charged cation, nonmetal becomes a negatively charged anion.
- Opposite charges create an electrostatic attraction, forming the ionic bond.
Electronegativity & Bond Polarity
- Electronegativity values to remember: H (2.1), B (2.0), C (2.5), N (3.0), O (3.5), F (4.0).
- Difference ≤ 0.4: Nonpolar covalent.
- Difference ≥ 0.5: Polar covalent.
- Large difference, especially metal–nonmetal: Ionic.
Key Terms & Definitions
- Electronegativity — an atom's ability to attract shared electrons.
- Ionic bond — bond formed by transfer of electrons between a metal and nonmetal.
- Covalent bond — bond formed by sharing electrons between nonmetals.
- Polar covalent bond — covalent bond with unequal sharing of electrons.
- Nonpolar covalent bond — covalent bond with equal sharing of electrons.
- Cation — positively charged ion.
- Anion — negatively charged ion.
- Hydrogen bond — strong intermolecular force when H is bonded to N, O, or F.
Action Items / Next Steps
- Memorize key electronegativity values for common elements.
- Practice classifying bonds as ionic, polar covalent, or nonpolar covalent based on electronegativity differences.
- Review the rules for indicating bond polarity with dipole arrows.