Overview
This lecture covers ionic bonding, introduces covalent bonding, and emphasizes the importance of intermolecular forces (IMFs) in determining chemical and physical properties, especially for future studies in biology and chemistry.
Introduction to Bonding and IMFs
- Ionic and covalent bonding are two major types of chemical bonds.
- Intermolecular forces (IMFs) control many physical properties, such as state of matter and solubility.
- IMFs are essential in biological molecules, cell structures, and functions.
Lewis Bonding Theory
- Lewis developed a theory explaining chemical bonds using valence electrons.
- Electrons are either transferred (ionic) or shared (covalent) between atoms.
- Bonding falls on a spectrum between perfect sharing and complete transfer.
- The octet rule states that atoms tend to have eight electrons in their valence shell, but there are many exceptions (e.g., hydrogen, boron, beryllium, expanded octets in phosphorus and sulfur).
- Valence electrons are key to bonding; core electrons rarely participate due to their strong attraction to the nucleus.
- Lewis structures (electron dot structures) help predict molecular polarity, stability, and geometry.
Bonding Theories Overview
- Three main theories: Lewis Theory/VSEPR, Valence Bond Theory (quantum mechanical), and Molecular Orbital Theory (quantum mechanical).
- All bonding theories emphasize the importance of valence electrons.
Ionic Compounds and Their Properties
- Ionic compounds form between cations (positively charged, no valence electrons in symbol) and anions (negatively charged, 8 valence electrons in brackets).
- Ionic bonds result from the transfer of electrons, e.g., Na + Cl → Na⁺ + Cl⁻.
- Ionic solids have a crystal lattice structure, maximizing attraction between oppositely charged ions.
- Ionic solids are hard, brittle, and have high melting points (usually >300°C).
- Ionic solids do not conduct electricity, but molten ionic compounds or aqueous solutions do because ions are free to move.
- Most ionic compounds are soluble in water; exceptions include compounds like calcium carbonate (CaCO₃).
Solubility and Examples
- Solubility varies; calcium carbonate is insoluble, while sodium chloride is highly soluble.
- Calcium carbonate is found in chalk, shells, and bones, highlighting why some ionic solids do not dissolve in water.
Key Terms & Definitions
- Ionic Bond — bond formed by the transfer of electrons between atoms.
- Covalent Bond — bond formed by the sharing of electrons between atoms.
- Lewis Structure — diagram showing valence electrons as dots around atoms.
- Octet Rule — tendency of atoms to have eight electrons in their valence shell.
- Crystal Lattice — ordered, repeating structure of ions in an ionic solid.
- Intermolecular Forces (IMFs) — forces between molecules affecting physical properties.
- Cation — positively charged ion.
- Anion — negatively charged ion.
- Electrolyte — substance conducting electricity when dissolved in water.
Action Items / Next Steps
- Begin the assigned lab on intermolecular forces (IMFs) by Monday or Tuesday.
- Review Lewis structures and VSEPR theory as covered in previous labs.
- Watch recommended videos and attend office hours if Lewis structures are unclear.