Overview
This lecture covers the differences between intramolecular and intermolecular forces of attraction, types of bonds, and how these forces determine physical properties of substances.
Types of Forces of Attraction
- Intramolecular forces of attraction hold atoms together within a molecule (e.g., bonds inside HCl).
- Intermolecular forces of attraction exist between molecules (e.g., HCl molecules attracting each other).
Intramolecular Forces
- Ionic bond: Formed by complete transfer of electrons from a metal to a non-metal, creating ions.
- Metals lose electrons to become positively charged cations; non-metals gain electrons to become negatively charged anions.
- Covalent bond: Formed when two non-metals share electrons.
- Non-polar covalent bond: Formed between atoms of the same or very similar electronegativity.
- Polar covalent bond: Formed when atoms of slightly different electronegativity share electrons unequally, creating partial charges.
Intermolecular Forces
- Intermolecular forces are weaker than intramolecular forces but affect boiling, melting point, density, and enthalpy.
- Dipole-dipole interactions: Attractive forces between the positive end of one polar molecule and the negative end of another.
- Ion-dipole interactions: Attraction between an ion and a polar molecule; common in solutions.
- Hydrogen bonding: Special dipole-dipole interaction with hydrogen bonded to N, O, or F; relatively strong among intermolecular forces.
- London dispersion forces: Weakest force; present in all molecules, strength increases with number of electrons.
Review Questions and Takeaways
- Covalent bonds form when atoms share electrons.
- Ionic bonds form when atoms transfer electrons, creating oppositely charged ions.
- Polar covalent bonds occur between atoms with slightly different electronegativities.
- Dipole-dipole forces exist between polar molecules with partial charges.
- Hydrogen bonds require H attached to N, O, or F.
- London dispersion forces are strongest in molecules with the most electrons.
Key Terms & Definitions
- Intramolecular forces — Forces holding atoms together within a molecule.
- Intermolecular forces — Forces acting between separate molecules.
- Ionic bond — Chemical bond formed by electron transfer, creating ions.
- Covalent bond — Chemical bond formed by electron sharing.
- Electronegativity — Atom's tendency to attract electrons.
- Dipole-dipole interaction — Force between polar molecules with partial charges.
- Ion-dipole interaction — Force between an ion and a polar molecule.
- Hydrogen bond — Strong intermolecular force involving H and N, O, or F.
- London dispersion forces — Weak attraction present in all molecules, stronger with more electrons.
Action Items / Next Steps
- Review properties of water and its molecular structure for next week's lesson.
- Prepare questions on intermolecular forces for discussion.
- Read about physical properties affected by intermolecular forces (boiling point, melting point, etc.).