Two six-descriptor models, each descriptor derived directly from molecular structure, were fitted to the normal boiling points (T b ) of ethane plus the 52 known chlorofluoroethanes by multiple linear regression (s ) 2.6 K, R 2 ) 0.998). Both models predict T b values of 351 ( 2 and 366 ( 2 K for unknown 1,1-dichloro-2-fluoroethane and 1,1,1-trichloro-2-fluoroethane, respectively. Several descriptors treat specially the atoms that remain exterior after X atoms in CH 2 X groups (X ) Cl, F) and H atoms in CHX 2 groups attach electrostatically to identical groups of adjacent molecules. Electrostatic repulsion between opposing CsX bonds reduces T b by 20-30 K for half of the compounds.

The authors are interested in building computer experiments that extend a student's experience beyond what is feasible or even possible in the laboratory at a given level. This article examines: computer experiments involving mathematical models; laboratory-equivalent computer experiments; and computer environment.

The singlet term of dioxygen with one doubly occupied π* orbital has lower energy than the singlet term with two singly occupied π* orbitals even though single occupancy is favored in the aufbau of atoms. A simple physical explanation based on orbital angular momentum explains this double occupancy.

This text is a thorough revision of the second edition, which appeared in 1983. The new edition continues to present extensive treatments of quantum principles and methods, atomic and molecular structure, and rotational, vibrational, and electronic spectroscopy.

We extend to heat capacity Cp the model of Vedamuthu, Singh, and Robinson (J. Phys. Chem. 1994, 98, 2222). This model and that of Bartell (J. Phys. Chem. B 1997, 101, 7573) fit successfully, even in the supercooled region, the temperature dependence of Cp, volume, and isothermal compressibility kappa(T). The Robinson model is superior for kappa(T). Tanaka's model (J. Chem. Phys. 2000, 112, 799) fails for C(p) even after correction of a derivational error. All three models assume that the liquid consists of low-density component 1 and high-density component 2. We conclude that Robinson's tactics, ignoring the intercomponent equilibrium constant and determining compositions solely from volumes, yield the most reliable compositions and individual-component properties. Our fits of the Robinson model to C(p) yield at 0 degrees C H(2) - H(1) of (135 +/- 35) J/g, H(1) - H(ice) of 0.8DeltaH(fus), and C(2) - C(1) of (0.1 +/- 0.7) J/K.g. The enthalpy difference between the components is largely responsible for the rapid change of C(p) at the lowest supercooled temperatures. We propose an adjustment to Speedy and Angell's (J. Chem. Phys. 1976, 65, 851) experimental values of kappa(T) for supercooled water.