Chemical Bond Types and Properties

Overview

This lecture explains how to distinguish between ionic, polar covalent, and nonpolar covalent bonds, using examples and examining the concepts of electronegativity and electron sharing.

Types of Chemical Bonds

• Ionic bonds typically form between a metal and a nonmetal.
• Covalent bonds usually form between two nonmetals.
• Ionic bonds involve a transfer of electrons, creating positive and negative ions.
• Covalent bonds involve the sharing of electrons between atoms.

Identifying Bond Types

• Use the periodic table: metals are to the left, nonmetals to the right of the dividing line.
• Electronegativity differences determine bond polarity:
  • Nonpolar covalent: EN difference ≤ 0.4 (equal sharing).
  • Polar covalent: EN difference ≥ 0.5 (unequal sharing).

Examples and Applications

• Br₂ (bromine molecule): two identical nonmetals, nonpolar covalent bond.
• CH₄ (methane): C and H are both nonmetals; C–H bond EN difference is 0.4; nonpolar covalent.
• C–O bond: both nonmetals, EN difference is 1.0; polar covalent bond.
• LiF (lithium fluoride): metal (Li) and nonmetal (F); ionic bond due to electron transfer.
• Ammonium nitrate (NH₄NO₃): contains both covalent bonds (within ions) and ionic bonds (between polyatomic ions), an exception to general rules.

Bond Formation Details

• In ionic bonds, metals lose and nonmetals gain electrons, creating full charges and electrostatic attraction.
• In covalent bonds, atoms share electrons to achieve a stable octet:
  • Nonpolar: equal sharing, no partial charges.
  • Polar: unequal sharing, resulting in partial charges (δ+ and δ−).

Key Terms & Definitions

• Ionic bond — bond formed by the transfer of electrons between a metal and a nonmetal, resulting in oppositely charged ions.
• Covalent bond — bond formed by sharing electrons between two nonmetals.
• Polar covalent bond — covalent bond with unequal sharing of electrons, creating partial charges.
• Nonpolar covalent bond — covalent bond with equal sharing of electrons, no partial charges.
• Electronegativity (EN) — a measure of an atom's ability to attract electrons in a bond.
• Polyatomic ion — a charged group of covalently bonded atoms.

Action Items / Next Steps

• Review periodic table locations for metals, nonmetals, and metalloids.
• Memorize common electronegativity values for key elements.
• Practice determining bond types and polarity for various compounds.