Overview
This lecture explains covalent bonds, their types, properties, the octet rule, and distinguishes between polar and nonpolar covalent bonds with examples and practice problems.
Covalent Bonds: Basic Concepts
- Covalent bonds form when atoms share pairs of electrons to achieve greater stability and a full valence shell.
- Nonmetals commonly form covalent bonds with other nonmetals, sharing 1–3 pairs of electrons.
- Electrons are shared equally only between identical atoms; otherwise, sharing is unequal due to differences in electronegativity.
Octet Rule
- The octet rule states atoms tend to achieve 8 valence electrons for stability by sharing, gaining, or losing electrons.
- Atoms share electrons via covalent bonds to fulfill the octet rule, aiming for a noble gas electron configuration.
- Exceptions to the octet rule exist and should be noted.
Types of Covalent Bonds
- Single bond: One pair of electrons shared; most stable and least reactive.
- Double bond: Two pairs of electrons shared; stronger and more reactive than single bonds.
- Triple bond: Three pairs of electrons shared; strongest but least stable and most reactive.
Polar vs. Nonpolar Covalent Bonds
- Polar covalent bonds: Electrons are unequally shared due to differing electronegativity, creating partial charges.
- Nonpolar covalent bonds: Electrons are shared equally, typically between identical atoms or atoms with similar electronegativity.
- Polar molecules have electrostatic potential, leading to phenomena like hydrogen bonding.
Lewis Structures and Electron Pairs
- A bond pair is a shared pair of electrons between atoms.
- A lone pair is an unshared pair of electrons on an atom.
Properties of Covalent Compounds
- Covalent compounds usually have lower melting and boiling points than ionic compounds.
- They may exist as gases, liquids, or solids, and generally do not conduct electricity or heat well.
Example Problems & Solutions
- Practice identifying types of bonds in molecules such as benzene, nitrate, and fluorine gas.
- Exercises on electron configuration to achieve noble gas structure.
- Determine molecular polarity for compounds like Oâ‚‚, HCl, and COâ‚‚.
- Identify true/false statements about covalent bonding.
- Match molecules to characteristics such as polarity and bond types.
Key Terms & Definitions
- Covalent bond — A chemical bond where two atoms share one or more pairs of electrons.
- Octet rule — The tendency of atoms to have eight electrons in their valence shell.
- Single bond — A bond formed by sharing one pair of electrons.
- Double bond — A bond formed by sharing two pairs of electrons.
- Triple bond — A bond formed by sharing three pairs of electrons.
- Polar covalent bond — A covalent bond with unequal electron sharing, resulting in partial charges.
- Nonpolar covalent bond — A covalent bond with equal electron sharing.
- Electronegativity — An atom's tendency to attract shared electrons.
- Bond pair — Shared pair of electrons in a covalent bond.
- Lone pair — Unshared pair of electrons on an atom.
Action Items / Next Steps
- Review provided example problems and attempt them independently.
- Study additional examples of octet rule violations.
- Practice drawing Lewis structures for various molecules.