Review of Atomic and Molecular Structure

More organic than inorganic compounds are known, firstly because carbon forms strong bonds to other carbon atoms. Although carbon is not unique in this, it is much the most successful element in the periodic table in this respect. Silicon, below carbon in the periodic table, does not readily form Si-Si bonds (it much prefers to form -Si-O-Si-O- chains) so the silicon life form beloved of science fiction writers stays firmly in the realm of fiction. Carbon also forms multiple (double and triple) bonds to other carbon atoms and forms strong and/or multiple bonds to most nonmetallic elements and to some metals. 

It has been possible to analyze organic molecules since the nineteenth century, and although the technology has been radically altered, the underlying principle of modern microanalysis is the same as was used then. What has changed is the availability of very high accuracy balances that can weigh reliably to 0.001 mg. Consider the nineteenth-century version of the analysis of ethanol. A 4.6 g sample of ethanol is burned in an excess (XS is a common abbreviation for excess) of 

FIGURE 1.1 Conversion of ammonium isocyanate to urea. Note. I hope you are familiar with the use of a capital Greek delta, A, to indicate heat. New symbols and acronyms will be explained the first time they are used, but they are also collected together in Appendix A. 

To convert these percentages to an empirical formula, we need to divide by the atomic weights  

Relative number of atoms of carbon = 52.2/12 = 4.35 Relative number of atoms of hydrogen = 13.0/1 = 13 Relative number of atoms of oxygen = 34.8/16 = 2.175 

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Before we begin our study of organic chemistry, we must review some basic principles. These concepts of atomic and molecular structure are crucial to your understanding of the structure and bonding of organic compounds. 

What follows is a nonmathematical treatment of the aspects of atomic and molecular structure that provides an adequate basis for understanding much of the chemistry presented later in this book. Much of this chapter should be a review of principles learned in earlier chemistry courses, which is intentional. More theoretical treatments of these topics can be found in the suggested readings at the end of this chapter. 

The purpose of this first computer laboratory is to review some of the fundamental concepts from classical physics, to understand what constitutes a solution to a problem in classical physics, and to introduce students to numerical solutions for the Newtonian equations of motion. QuickBASIC programs have been written which use PC graphics to display the trajeaory of an electron in the Thomson plum pudding model of the atom, the Bohr atom, and a classical model for the hydrogen-molecule ion. This early review of classical physics helps students appreciate more fully how fundamentally different quantum theory is. The material in this exercise is frequently used as a leaure demonstration to support a classroom lecture on the precursors to the quantum theory of atomic and molecular structure. 

Book review of The Fine Structure of Matter. Part I. X-Rays and the Structure of Matter. Vol. II of A Comprehensive Treatise of Atomic and Molecular Structure by C. H. Douglas Clark (New York John Wiley and Sons, 1937). J. Am. Chem. Soc. 60 (1938) 988. 

Abstract. BERTHA is a 4-component relativistic molecular structure program based on relativistic Gaussian (G-spinor) basis sets which is intended to make affordable studies of atomic and molecular electronic structure, particularly of systems containing high-Z elements. This paper reviews some of the novel technical features embodied in the code, and assesses its current status, its potential and its prospects. 

The theories of surface structure and bonding have been reviewed. It should be clear to the reader that surface structural chemistry is indeed a frontier area for both theorists and experimental researchers. From an experimentalists viewpoint the data base of atomic and molecular surface structures is very small at present. Most investigations have been carried out on flat, low Miller index surfaces of monatomic solids, either clean or with atomic or small molecules as adsorbates. 

It has not been possible within the space available to give a completely comprehensive account of all of the developments which have recently been made in the field of basis set construction, a field that forms the foundation upon which the vast majority of contemporary atomic and molecular electronic structure studies are based. This review has necessarily been selective but should provide the reader with an up-to-date account of the most important aspects of current thinking on the algebraic approximation. It has concentrated on the construction of basis sets for electron correlation energy calculations, for calculations of atomic and molecular properties (other than the energy), for the study of small interaction energies such as van der Waals interactions, for the determination of relativistic effects and for studies of extended molecular systems. 

With the use of increasingly parallel architectiues in modem computers and the growing awareness that basis set truncation errors are frequently the dominant source of error in contemporary electronic structure studies, significant improvements in the accuracy of such studies can be expected in the new few years. The key issue in making this progress is the construction of large basis sets which will afford an accurate representation of atomic and molecular wavefunctions whilst avoiding computational linear dependence. This review was completed in September, 1985. 

In the first eight chapters devoted to carbides, several basic principles are reviewed such as atomic and molecular structure, crystalline arrangement, type of bond, etc. These principles also qiply to nitrides but are not repeated and only cross-referenced. Whenever possible, the relationship between structure, properties, and applications is stressed throughout the book. 

In order to facilitate the discussion of some aspects of cluster chemistry-especially those related with bonding and its relationship with chemical and structural properties of the compounds-it is convenient to review briefly the fundaments of current bonding concepts. Some germane aspects of the atomic and molecular structure will be therefore summarized in the next sections. As an application of such concepts and also as an introduction to metal clusters, the discussion of some aspects of the metal-metal multiple bonding in dinuclear compounds is also included in this Chapter. 

Consistent with the philosophy that less is better than more, this book does not contain the traditional chapters reviewing or expanding on atomic and molecular structure and other topics. Rather, it takes the view that these topics are developed adequately in most introductory courses and textbooks and need not be dwelt upon here. As a result, the book jumps directly into presentations of topics central to inorganic chemistry. 

GAMESS stands for general atomic and molecular electronic structure system (we reviewed a version dated Dec. 2, 1998). It is an ah initio and semiempirical program, and has seen the most widespread use for ah initio calculations. The ASCII input hie format is usable but somewhat more lengthy than some other programs. The fact that GAMESS is a free, high-quality software makes it a favorite of many academic researchers. 

The quantum theory of spectral collapse presented in Chapter 4 aims at even lower gas densities where the Stark or Zeeman multiplets of atomic spectra as well as the rotational structure of all the branches of absorption or Raman spectra are well resolved. The evolution of basic ideas of line broadening and interference (spectral exchange) is reviewed. Adiabatic and non-adiabatic spectral broadening are described in the frame of binary non-Markovian theory and compared with the impact approximation. The conditions for spectral collapse and subsequent narrowing of the spectra are analysed for the simplest examples, which model typical situations in atomic and molecular spectroscopy. Special attention is paid to collapse of the isotropic Raman spectrum. Quantum theory, based on first principles, attempts to predict the. /-dependence of the widths of the rotational component as well as the envelope of the unresolved and then collapsed spectrum (Fig. 0.4). 

In this review we will give an overview of the properties (asymptotics, shell-structure, bond midpoint peaks) of exact Kohn-Sham potentials in atomic and molecular systems. Reproduction of these properties is a much more severe test for approximate density functionals than the reproduction of global quantities such as energies. Moreover, as the local properties of the exchange-correlation potential such as the atomic shell structure and the molecular bond midpoint peaks are closely related to the behavior of the exchange-correlation hole in these shell and bond midpoint regions, one might be able to construct... 

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