CH 102 Lecture 1Outline of Current Lecture I. Cohesive forcesII. Ionic BondingIII. Covalent BondingIV. Dispersion ForcesV. Dipole–Dipole Attractions: Interactions between Polar MoleculesVI. Dipole-Dipole Attraction EnergyVII. Hydrogen Bonding: A Special Case of Dipole–Dipole InteractionCurrent LectureI. Cohesive forcesa. Bonding forcesi. Ionic bondingii. Covalent bondingiii. Metallic bondingb. Non-bonding forcesi. Dispersion forcesii. Dipole-dipole attractioniii. Ion-dipole attractioniv. Hydrogen bondingII. Ionic Bondinga. All you need to know about ionic bonding is that opposite charges attractb. Lattice energy: the energy released when one mole of an ionic compound is formed from its ions in the gas phaseIII. Covalent Bondinga. Chemical bonds made by sharing electrons between the atoms making the bondsb. Molecular orbital theory provides a basis for understanding chemical bonding in general and covalent bonding in particularIV. Dispersion Forcesa. Fluctuations in the electron distribution in atoms and molecules result in a temporary dipole.i. Region with excess electron density has partial (–) charge.ii. Region with depleted electron density has partial (+) charge.b. The attractive forces caused by these temporary dipoles are called dispersion forces.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. They are also known as London forces or van der Waals forces.ii. As a temporary dipole is established in one molecule, it induces a dipole in all the surrounding molecules.c. All molecules and atoms will have dispersion forces.d. The energy of interaction depends on the polarizibility of each species and on thedistance between themV. Dipole–Dipole Attractions: Interactions between Polar Moleculesa. Polar molecules have a permanent dipole.i. Bond polarity and molecular geometry (shape) determine the substances polarityii. Dipole momentb. The permanent dipole adds to the attractive forces between the molecules, raising the boiling and melting points relative to nonpolar molecules of similar size and shape.VI. Dipole-Dipole Attraction Energya. Energy of Interaction between two polar molecules A and Bi. E = -(2∙μA∙μB)/(4πε0r3)b. Wherei. μA and μB are the first ionization potentials for each speciesii. ε0 is the permittivity of free space, a physical constantiii. r is the distance between the dipolesc. The energy of interaction depends on the dipole moment of each molecule and on the distance between themi. A short range effectVII. Hydrogen Bonding: A Special Case of Dipole–Dipole Interactiona. When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it.i. O—H, N—H, or F—Hb. Because hydrogen has no other electrons, when its electron is pulled away, the nucleus becomes deshielded, exposing the H proton.c. The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules.d. Hydrogen bonds are very strong intermolecular attractive forces.e. Stronger than dipole–dipole or dispersion forcesf. Substances that can hydrogen bond will have higher boiling points and melting points than similar substances that cannot.g. But hydrogen bonds are not nearly as strong as chemical bonds. (2–5% the strength of covalent
View Full Document
Unlocking...