Lecture contents

Fall 2017

Department of Chemistry | Boston University

For each lecture: there is a link to the PDF of the PowerPoint slides used in that lecture and a link to the lecture recording, showing the notations made to each slide during the lecture.

Lecture 1, Wednesday, September 6, 2017
Begin Mahaffy et al., chapter 2: Building blocks of materials.
Estimate the number of atoms that the lecture hall can hold. Estimate the volume occupied by the in the lecture hall after the air has been liquefied.
Lecture slides and lecture recording.

Lecture 2, Friday, September 8, 2017 Complete calculation of the volume occupied by the in the lecture hall after the air has been liquefied. Chemistry depends on the number of electrons in the electron cloud but not on the mass of the nucleus. Therefore, isotopes of an elements behave the same chemically. The atomic mass unit u is 1/12 the mass of one C-12 atom. Exactly 12 g of C-12 contains Avogadro's constant, NA, of atoms. Therefore, 1 u = 1 g/NA.
Lecture slides and lecture recording.

Lecture 3, Monday, September 11, 2017 How a mass spectrometer works. What a mass spectrum is. "Mass spectrum" of a chemistry class. Fractional abundances and how to use them. Average mass in terms of fractional abundances.
Lecture slides and lecture recording.

Lecture 4, Wednesday, September 13, 2017 Relative atomic mass, Ar, is the (unitless) ratio of the mass of an isotope to the mass of 1/12 of one `12C atom. Atomic weight is the (unitless) average of the relative atomic masses of the isotopes of an element. Molar mass, M, is the mass in grams numerically equal to the atomic weight, and so it is the mass in grams of NA "average atoms" of an element. Mole is NA atoms or molecules. Using mass to count numbers of atoms or molecules.
Lecture slides and lecture recording.

Lecture 5, Friday, September 15, 2017
Begin Mahaffy et al., chapter 3: Models of structure to explain properties.
Common monoatomic ions and patterns. Common polyatomic ions. Ionic compounds dissolve by formation of hydrated ions. These ions do not further come apart in water. Molecular mass spectra. The molecular ion is composed of the entire molecule. Constitutional isomers have the same empirical formula but different chemical structure. They have the same molecular ion, but otherwise different peaks in their mass spectra, since, in general, constitutional isomers fragment in different ways.
Lecture slides and lecture recording.

Lecture 6, Monday, September 18, 2017 Mass spectra can be used to identify elements in a molecule. C, O, N, H, and F each have only one important isotope. Cl has two important isotopes" 35Cl:37Cl::3:1. Br has two important isotopes" 79Br:81Br::1:1. Effect of Br and Cl on peaks in mass spectra. Light acts as oscillating tugs on charge clouds in matter.
Lecture slides and lecture recording.

Lecture 7, Wednesday, September 20, 2017 Molecular ion peaks example: CH2Cl(2) molecular ion peaks are at 84:86:88 in the ratio 9:6:1. Region of electromagnetic spectrum: X-ray, UV, visible, IR, microwave, radio.
Demonstration: Lighter atoms vibrate faster; atom bonded more strongly vibrate faster.
Demonstration: The more dissimilar bonded atoms are, the faster the lighter atoms vibrates.
CDF animation: Effect of relative mass and bond strength on vibration frequency.
Lecture slides and lecture recording.

Lecture 8, Friday, September 22, 2017 Regions of the IR spectrum: fingerprint region, up to 1500 cm-1; double-bond region, 1500-2000 cm-1; triple bond region, 2500-2000 cm-1; and X-H region, above 2500 cm-1. Wavenumber, ν̃, is the reciprocal of the wavelength in cm, 1/λ; therefore wavenumber is the number of wavelengths that can fit in 1 cm. Practice with wavelength, frequency, and wavenumber.
Lecture slides and lecture recording.

Lecture 9, Monday, September 25, 2017 IR (infrared) spectra. How light causes oscillatory motion in matter.
Lecture slides and lecture recording.

Lecture 10, Wednesday, September 27, 2017
Begin Mahaffy et al., chapter 4: Carbon compounds.
Suggestion on how to work with the textbook. How the atmosphere is warmed. Collisional heating of the atmosphere, http://goo.gl/vQ0Nz. IR windows in the atmosphere, http://goo.gl/I8IGz. Timeline of Earth's average temperature ..., http://xkcd.com/1732/
Lecture slides and lecture recording.

Lecture 11, Friday, September 29, 2017
Begin Mahaffy et al., chapter 5: Chemical reactions, chemical equations.
What a chemical equation tells us. Balancing chemical equations by inspection. Stoichiometry: Amounts in chemical transformations. Limiting reagents.
Lecture slides and lecture recording.

Lecture 12, Wednesday, October 4, 2017 Review of stoichiometry: Amounts in chemical transformations. Limiting reagents. Percent yield.
Begin Mahaffy et al., chapter 6: Chemical of water, chemistry in water.
Hydrogen bonding in ice and water. Heat versus temperature. Heat capacity.
Lecture slides and lecture recording.

Lecture 13, Friday, October 6, 2017 Vapor pressure and boiling.
Lecture slides and lecture recording.

Lecture 14, Tuesday, October 10, 2017 Review: Vapor pressure and boiling. Intermolecular versus intramolecular forces. Hydrogen bonding. Dipole-dipole interaction (polarity).
Lecture slides and lecture recording.

Lecture 15, Wednesday, October 11, 2017 Molecular polarity arises when bond dipoles do not cancel. Dipole-dipole interaction can be attractive or repulsive.
Lecture slides and lecture recording.

Lecture 16, Friday, October 13, 2017 (London) Dispersion interaction. Relative effect of electron cloud size (molecular weight), polarity, and hydrogen bonding on boiling points.
Lecture slides and lecture recording.

Lecture 17, Monday, October 16, 2017 Rationale of relative boiling points of HF, H2O, and NH3: Water can form twice as many hydrogen bonds. Predicting relative boiling points. How ionic solids dissolve in water.
Lecture slides and lecture recording.

Lecture 18, Wednesday, October 18, 2017 Rationale of relative boiling points of HF, H2O, and NH3: More on how ionic solids dissolve in water. Microscopic view of aqueous ionic solution molarity. Solubility rules.
Lecture slides and lecture recording.

Lecture 19, Friday, October 20, 2017 Precipitation reactions. Concentrations after precipitation.
Lecture slides and lecture recording.

Lecture 20, Monday, October 23, 2017 Ionization of molecular solutes. Self-ionization (autoionization) of water. Acid-base reactions: Competition for protons, H+. Common acids and bases.
Lecture slides and lecture recording.

Lecture 21, Wednesday, October 25, 2017 Oxidation-reduction equations. Lewis acid-base reactions and complexation.
Begin Mahaffy et al., chapter 7: Chemical reactions and energy flows.
First law of thermodynamics. Signs of heat and work.
Lecture slides and lecture recording.

Lecture 22, Friday, October 27, 2017 System versus surroundings. Detecting heat, q. In chemical reactions, there is temperature change in the surroundings, but the system temperature remains constant. Predicting the sign of heat. Detecting work, w.
Lecture slides and lecture recording.

Lecture 23, Wednesday, November 1, 2017 Practice with the first law of thermodynamics. The change in internal energy, ΔU = qV, is the heat flow when a chemical reaction is carried out in a sealed, rigid container so that volume is constant.
Lecture slides and lecture recording.

Lecture 24, Friday, November 3, 2017 The change in enthalpy, ΔH = qP, is the heat flow when a chemical reaction is carried out in a open container so that pressure is constant. Use energy diagrams to determine the relation between qPH) and qVU)
Lecture slides and lecture recording.

Lecture 25, Monday, November 6, 2017 Temperature equilibration (heat leveling). Heating curves. Enthalpy change of reaction.
Lecture slides and lecture recording.

Lecture 26, Wednesday, November 8, 2017 Hess's law. Standard states and standard enthalpy change of reaction. Standard enthalpy change of formation.
Lecture slides and lecture recording.

Lecture 27, Friday, November 10, 2017 Using enthalpy changes of formation to compute enthalpy change of reaction. Bond enthalpies. Using bond enthalpies to estimate enthalpy change of reaction.
Lecture slides and lecture recording.

Lecture 28, Monday, November 13, 2017 Using bond enthalpies to estimate enthalpy change of reaction. Using bond enthalpies to estimate enthalpy change of reaction give poor results if some substances are liquids or gases.
Begin Mahaffy et al., chapter 8: Modeling atoms and their electrons.
Review: What light is and how it interacts with matter. Natural frequencies of atoms.
Lecture slides and lecture recording.

Lecture 29, Wednesday, November 15, 2017 Light and matter exchange energy smoothly and slowly
CDF animation: H atom 1s-2p transformation by light.
Light energy is exchanged in tiny amounts called photons. Using light-matter resonance frequencies to construct energy diagrams of matter. Electron waves and quantization (de Broglie): Integer number of loops (half-wavelengths); more loops,more energy.
Lecture slides and lecture recording.

Lecture 30, Friday, November 17, 2017 H atom electron clouds.
PDF: Hydrogen atom family album.
H atom photon energies. Rydberg energy (Ry) and electron volt (eV). He+ , Li2+ , etc., photon energies. Photoionization (photoelectric effect).
Lecture slides and lecture recording.

Lecture 31, Monday, November 27, 2017 Revisit: Light and matter exchange energy smoothly and slowly
CDF animation: H atom 1s-2p transformation by light.
Light mixes together electron waves of differing numbers of loops (differing principal quantum numbers).
H atom photon energies: Balmer's formula
Lecture slides and lecture recording.

Lecture 32, Wednesday, November 29, 2017 H atom photon energies: Beyond Balmer's formula. He+ , Li2+ , etc., photon energies.
Lecture slides and lecture recording.

Lecture 33, Friday, December 1, 2017 Question about H atom interaction with light: Light can transform an s electron cloud only to a p electron cloud.
CDF animation: H atom 1s-2p transformation by light.
Light can transform a p electron cloud into a d electron cloud.
CDF animation: H atom 2p-3d transformation by light.
Light cannot transform an s cloud into another s cloud directly. This can only be done indirectly, say as 1s to 3p, and then 3p to 2s. Photoionization (photoelectric effect). Review: Lewis structures and graphical method to determine formal charge and oxidation number.
Lecture slides and lecture recording.

Lecture 34, Monday, December 4, 2017 Review: Electron clouds. Review: Lewis structures, formal charge and oxidation number. More than one electron: Orbital (yikes!) approximation. Electrical shielding from the nucleus of one electron by others.
Lecture slides and lecture recording.

Lecture 35, Wednesday, December 6, 2017 Electrical shielding from the nucleus of one electron by others.
PDF: Shielding in Li 1s22s and Li 1s22p. Building electron configurations of many-electron atoms. Electron spin (intrinsic magnetic moment). Energy order of relative spins (Pauli principle and Hund's rules)
Lecture slides and lecture recording.

Lecture 36, Friday, December 8, 2017 Complete: Building electron configurations of many-electron atoms.
Begin Mahaffy et al., chapter 10: Modeling bonding in molecules.
Bonding in diatomic (two-atom) molecules: Combining AOs (atomic orbitals) makes MOs (molecular orbitals). PDF: Bonding in diatomic molecules.
CDF animation:
Bonding and antibonding MOs from in-phase (constructive interference) and out-of-phase (destructive interference) combinations of AOs
. Constructive interference of AOs results in bonding MOs; destructive interference of AOs results in antibonding MOs.
Lecture slides and lecture recording.

Lecture 37, Monday, December 11, 2017 AO-MO correlation diagrams summarize the combined effect of changing kinetic and potential energy, in bonding (in-phase) and antibonding (out-of-phase) combinations of AOs. Bond order: H2+ to Be2 (!). σ and π bonding.
CDF animation: 2p MOs.
Electron configuration and bond order from B2 to Ne2 (!). Magnetic properties of these molecules show that from B2 to N2 the 2pπ bonding orbitals are more stable than the 2pσ bonding orbital, and from O2 to F2 the 2pπ* antibonding orbitals are more stable than the 2pσ* antibonding orbital.
Lecture slides and lecture recording.