Chemistry from First Principles

verfasst von: Jan C. A. Boeyens

Verlag: Springer Netherlands

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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"Chemistry from First Principles" examines the appearance of matter in its most primitive form. It features the empirical rules of chemical affinity that regulate the synthesis and properties of molecular matter, analyzes the compatibility of the theories of chemistry with the quantum and relativity theories of physics, formulates a consistent theory based on clear physical pictures and manageable mathematics to account for chemical concepts such as the structure and stability of atoms and molecules. This text also explains the self-similarity between space-time, nuclear structure, covalent assembly, biological growth, planetary systems, and galactic conformation.

Inhaltsverzeichnis

Frontmatter

A New Look at Old Theories

1. Historical Perspective

Any scientific pursuit starts out with an examination of objects and phenomena of interest and proceeds by the accumulation of relevant data. As regularities emerge, classification of related facts inevitably leads to the formulation of laws and hypotheses that stimulate experimental design, until better understanding culminates in a general theory. The wider the field of enquiry the more cumbersome the development of theoretical understanding would be. In a subject like chemistry with so many facets it is even more difficult to recognize the central issues to feature in a comprehensive theory.

Chemistry has its roots in alchemy, best described as the most extensive project in applied research of all time. It pursued a single-minded search for the philosopher’s stone and the elixir of life for more than a thousand years, through the middle ages and into the modern era. It relied with dogmatic certainty on a given theory that clearly specified the powers of the philosopher’s stone and its hidden existence. No room was left for improvement or falsification of the theory and failed experiments were documented with the sole purpose of avoiding the same mistakes in future. Claims of successful production of alchemical gold were fiercely protected secrets and the only visible benefits were in the isolation, purification and characterization of theoretically irrelevant chemical substances. Alchemy, in this sense, is the exact antithesis of scientific endeavour. In science there is no authority or infallible theory. Any theory that claims final validity stifles further progress.

2. The Important Concepts

The universally accepted theory of chemistry as a synthesis of the 19th century notions of chemical affinity, molecular structure and thermodynamics, with the theories of physics, which developed in the early 20th century, has gained almost universal acceptance as a closed set of concepts under the heading of Physical Chemistry. For more than fifty years textbooks on the subject have been revised and reorganized with the addition of preciously little new material. Today, these treatises are standardized over the world and translated into all relevant languages, emulating the standard models of particle physics and cosmology.

The seminal theories are respected as received wisdom, all flaws have been rationalized and the only remaining challenge is to dress up the old material with electronic wizardry, as if theoretical innovation ceased to operate in 1950. If indeed, there is nothing new or controversial in theoretical chemistry, with everything securely locked up in computer software at different levels of theory, the excitement is gone and dissident views are taboo. However, the nature of knowledge and of science is different. There are no closed books, not even on Euclidean geometry, and certainly not on chemistry. The standard models neglect to tell us how matter originates, what limits the variety of atomic matter, what is a chemical bond, and why is it necessary to assume the most fundamental concept that dictates the stability of matter – the exclusion principle – on faith? Even if these questions cannot be answered, they should be asked continually, maybe from a point of view overlooked by the founding theorists. It is in this spirit that the important concepts, fundamental to chemistry, will be re-examined in Part I of this work.

3. The Quantum Quandary

Apart from a few ‘minor’ unsolved problems the science of physics had reached such maturity towards the end of the 19th century that leading physicists could claim with confidence that no major new developments could be foreseen. Even Max Planck, who inaugurated one such development, is purported to have dissuaded young scientists from following careers in physics. This assessment, although misguided in retrospect, speaks for total accord among those scientists on the understanding of their science, without any need for, or arguments about alternative interpretations. Such agreement can only arise from absolute certainty on the basic premises of the subject. The cornerstone of 19th century physics, Newtonian mechanics as developed in the hands of Lagrange, Hamilton, Jacobi and others, was universally accepted and understood.

The situation, one hundred years on, could hardly be more different. The interpretation of quantum mechanics, which came to replace the Newtonian system, is as hotly disputed as ever and the common ground with the theory of relativity remains elusive and vague. The reason for the discord must lie somewhere in the transition from the classical to the new non-classical paradigm. What is proposed here, is to retrace the steps that led to the emergence of the new theoretical models, in an attempt to identify the point of conceptual bifurcation.

Alternative Theory

4. The Periodic Laws

The most conspicuous failure of quantum physics, as a theory of chemistry, is the demonstrated inability to account in detail for the observed periodic order of the elements, the single most important feature of theoretical chemistry. The importance of this failure, if not completely ignored, is routinely underplayed in elementary chemistry texts, by statements such as [61]:

“We need not dwell on these exceptions beyond noting that they occur.”

A supposedly better informed source [51] states:

“…. the 4s state, which has a higher energy than the 3d state in hydrogen, is depressed because of its low angular momentum, which causes its orbital to be large at small r, where it can feel the full nuclear attraction.”

Still, these non-explanations¹ are generally considered sufficient to rationalize all discrepancies between observed and predicted electronic configurations.

5. Chemical Interaction

The axioms that underpin any theory of chemical interaction were clearly stated by Kekulé, in the middle of the 19th century, as a theory of chemical affinity [16]. Restated in modern terminology:

interatomic interaction is defined to be mediated by electrons;
radicals that remain intact during chemical reaction are holistic molecular fragments;
the way in which atoms stack together in molecules or radicals depend on the electronic configuration of the elements concerned;
molecular shape — left undefined by Kekulé — can be ascribed to the minimization of orbital angular momentum.

To build a theory on these axioms it is necessary to have a clear understanding of the assumed nature of the electron and the conditions under which electron exchange between atoms becomes possible. These conditions will be taken to define an atomic valence state. The electronic configuration that dictates the mode of interaction between atoms of different elements will be interpreted to define the quantum potential energy of a valence electron in the valence state of an atom. This quantity will be shown to correspond to what has traditionally been defined empirically as the electronegativity of an atom.

6. Structure Theory

The molecular concept has become so central in chemistry that understanding of chemical events is commonly assumed to consist of relating experimental observations to micro events at the molecular level, which means changes in molecular structure. In this sense molecular structure is a fundamental theoretical concept in chemistry. As the micro changes are invariably triggered by electron transfer, the correct theory at the molecular level must be quantum mechanics. It is therefore surprising that a quantum theory of molecular structure has never developed. This failure stems from the fact that physics and chemistry operate at different levels and that grafting the models of physics onto chemistry produces an incomplete picture.

Although the physics model may give a reasonable qualitative account of chemical concepts, such as chemical cohesion, it fails at the quantitative level, because essential factors are ignored. The most important factor is the environment. The free atom of physics represents a universe, completely empty, except for a solitary atom. Such an atom can never explain chemical effects, which occur because of the interaction of an atom with its environment. When the total environment is taken into account one deals with the familiar classical macro world. Between the two extremes is chemistry and it is important to know whether to describe chemical entities, like molecules, in classical or non-classical terms.

7. Chemical Change

The magic of chemistry comes with thrills and excitement, flashy reactions and fireworks, with colour and sound. It is not bonding and structure that grab the imagination, but spectacle and change. Here is the topic that tells the real story of chemistry. Chemical change, more than anything, happens in a crowded environment. Factors of importance are the state of aggregation, material concentration, temperature and pressure, collectively known as thermodynamic conditions. Students of chemistry, even at the elementary level, should be familiar with thermodynamic models of chemical reactivity. For a concise revision refer to [15]. A brief summary follows.

8. The Central Science

Chemistry, the link between earth and life sciences, is often considered as The Central Science. This description is equally appropriate in the reductionist hierarchy of knowledge, which ranges from philosophy through mathematics, physics, chemistry and biology, towards the behavioural sciences. The common principles that emerge in the periodic arrangement of matter, as a numerical function of either nucleons or electrons, in the nature of covalent interaction, in botanical phyllotaxis and in the observed gaps of the asteroid belt, suggest a central role for chemistry in an even more fundamental way. The golden ratio, Fibonacci numbers and Farey sequences feature prominently in all of these constructs. Should the same geometrical principle decide the planetary structure of the solar system and the structure of spiral galaxies, a universal self-similarity mediated by the symmetry of space-time could be inferred.

The parallel which was drawn by Nagaoka between the rings of Saturn and atomic structure is based on such self-similarity. Although the Saturnian ring system is stabilized by gravitation, with angular momentum, and the atom, which is stabilized electrodynamically, has no angular momentum, the structural difference is one of dimension only. In order to quench the orbital angular momentum, electronic rings are required to be spherical.

Backmatter

Titel: Chemistry from First Principles
verfasst von: Jan C. A. Boeyens
Verlag: Springer Netherlands
Electronic ISBN: 978-1-4020-8546-8
Print ISBN: 978-1-4020-8545-1
DOI: https://doi.org/10.1007/978-1-4020-8546-8