Physical chemistry conceptual understanding

An integral part of a student s education in physical chemistry is laboratory/practical work. While it is generally accepted that the main purposes of laboratory work are to teach hand skills and to illustrate theory, significant problems have been identified in the science education literature about the laboratory courses, and in particular about the ineffectiveness of laboratory instruction in enhancing conceptual understanding (135, 136), and unrealistic in its portrayal of scientific experimentation (137). 

In this chapter, we turn to problems of quantum chemistry and of many-electron atomic and molecular physics for which fhe desideratum is the quantitative knowledge and easy conceptual understanding of dynamical processes and phenomena thaf depend explicifly on time. We focus on a theoretical and computational approach which computes q>(q,t) by solving nonperturbatively the many-electron TDSE for unstable states of atoms and small molecules. The time evolution of fhese states is caused either by the time-independent Hamiltonian, Ham ( -g-/ case of time-resolved autoionization—see below) or by the time-dependent Hamiltonian, H t) = Ham + Vext(f), where Vext(f) is the sum of the identical one-electron operators that couple the field of a strong pulse of radiation to the electronic and nuclear moments of N-electron atomic or molecular states of inferest, thereby producing, during and at the end of the interaction, final stafes in the ionization or the dissociation continua. 

Physical chemistry tutorials reinforce conceptual understanding. Over 460 tutorials are available in MasteringChemistry for Physical Chemistry, including new ones on The Cyclic Rule and Thermodynamic Relation of Proofs. 

In principle, knowledge of an atom or molecule s electronic structure i.e., the quantum mechanical wavefunction) would enable one to predict both its physical properties and its chemical behavior, including the outcome of reactions with other atoms or molecules whose electronic structure are equally well known (cf Daudel, 1973 Daudel et al., 1982). But because the Schrddinger equation cannot be solved exactly for any system more complicated than the hydrogen atom, the wavefunction of atoms and molecules must be approximated. Spectroscopy provides us with an observational link between the macroscopic and microscopic realms of matter, and it has been both a guide to our conceptual understanding of matter and a means to approximate parameters that are used in semiempirical computational chemistry (cf. Segal, 1977). 

With these goals in mind, the book puts an emphasis on conceptual understanding and does not use detailed mathematical derivations. Lower-division course knowledge in physics, chemistry, and math is assumed throughout, with some refreshers and the appendices to fill in some mathematical details. The aim is not to provide a rigorous theoretical description of any particular subject because this work has already been done very well by many authors at a graduate level in the specialized books among those referenced at the end of each chapter. 

Finally, there are computable properties tliat do not correspond to physical observables. One may legitimately ask about tlie utility of such ontologically indefensible constructs However, one should note that unmeasurable properties long predate computational chemistry - some examples include bond order, aromaticity, reaction concertedness, and isoelec-tronic, -steric, and -lobal behavior. These properties involve conceptual models that have proven sufficiently useful in furthering chemical understanding that they have overcome objections to their not being uniquely defined. 

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