ELECTRONIC STRUCTURES AND PROCESSES

INTRODUCTION

• In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure. It concerns the way electrons can be distributed in the orbital of the given system (atomic or molecular for instance).

The first period

• Hydrogen has its only electron in the 1s orbital - 1s1, and at helium the first level is completely full - 1s2.

The second period

• Now the 2p levels start to fill. These levels all have the same energy, and so the electrons go in singly at first.

• B 1s22s22px1

• C 1s22s22px12py

1

• N 1s22s22px12py

12pz1

The next electrons to go in will have to pair up with those already there.

• O 1s22s22px22py

12pz1

• F 1s22s22px22py

22pz1

• Ne 1s22s22px22py

22pz2

The third period

• all the second level orbitals are full, and so after this we have to start the third period

• The pattern of filling is now exactly the same as in the previous period, except that everything is now happening at the 3-level.

short version

Mg 1s22s22p63s2 [Ne]3s2

S1s22s22p63s23px

23

py13pz

1

[Ne]3s23px23py

13pz

1

Ar1s22s22p63s23px

23

py23pz

2

[Ne]3s23px23py

23pz

2

The beginning of the fourth period

• At this point the 3-level orbitals aren't all full - the 3d levels haven't been used yet. But if you refer back to the energies of the orbitals, you will see that the next lowest energy orbital is the 4s - so that fills next.

• K 1s22s22p63s23p64s1

• Ca 1s22s22p63s23p64s2

APPLICATIONS OF ELECTRONIC STRUCTURES

Organic Chemistry

• organic chemistry is generally the second course sequence for students majoring in chemistry or chemical engineering

Fundamentals of Structure-Reactivity Relationships

• From their first courses in chemistry, all students have at least a rudimentary knowledge of acids as proton donors. Thus, a simple computational exercise they can carry out the first time they use modeling software is one in which they construct a set of related organic protic acids and model electronic charge density associated with the acid proton.

Experimental Design and Formulation of Testable Hypotheses

• We have used two other somewhat less usual pedagogical applications of the computational features of modeling software to support the laboratory portion of the organic chemistry course.

Transition States and Reaction Mechanisms

• From about mid-way through a first course in organic chemistry references to reaction mechanism, transition state structures, and the interplay of thermodynamic control and kinetic control are frequent.

Physical Chemistry

• The physical chemistry curriculum can be divided into the following major segments: thermodynamics and thermochemistry, chemical kinetics, and quantum chemistry.

Quantum Chemistry

• When using most electronic structure computational packages, the user is faced with a number of different computational approaches: molecular mechanics, ab-initio, semi-empirical, and density functional.

Thermo chemistry

• An important topic in physical chemistry is the ability to obtain thermochemical information on unstable species or reaction intermediates and transition state structures.

Chemical Kinetics

• An excellent example of using electronic structure computations is to have students construct a potential energy diagram along a reaction pathway.

Chromatography

• As our first example, we describe how electronic structure computations can be used effectively in developing a student's understanding of chromatographic separations.

Spectroscopy

• Another important topic in analytical chemistry is spectroscopy, the study of the interaction of light with matter.

Predicting Trends

• In advanced analytical chemistry courses it is possible to enhance understanding of spectroscopic trends by performing calculations for a particular family of molecules.

Vibrational Spectroscopy

• At this point we wish to address briefly the applications of electronic structure computations in advanced analytical spectroscopy courses and their potential overlap with advanced inorganic courses.