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This page reviews the chemogenesis analysis and places it in the context of chemical education.

Chemistry in Crisis

The number of students studying chemistry at school and university is falling and there are many reasons why this should be, including:

  • Some of the new and emerging bioscience and drug discovery technologies are chemistry in all but name: DNA structure & function, the polymerase chain reaction, molecular biology, proteomics, etc., yet professionals in these areas are considered to be biologists rather than chemists.
  • Chemistry does not have a very green image in this environmentally conscious age.
  • Analytical science is changing from titrations with burettes, pipettes and conical flasks into an instrumental and IT based science.
  • Students realise that to be a professional chemist – or a professional physicist, biologist, statistician, etc., – it is essential to have a PhD, a qualification that requires many years of dedicated study for moderate financial reward.

I suggest that, in addition, there is a chemical education problem which is causing students to reject the subject. I do not mean that chemists are bad teachers. On the contrary, chemistry is difficult and it is essential to be a good teacher to convey the complexity and richness of the subject.

I hold that there is a structural difficulty concerning chemical reactions & chemical reactivity:

  • Students of chemistry encounter many and various chemical reactions during their studies, but they are not given an organising system – or schema – onto which this reaction chemistry information can be mapped.
  • Chemistry textbooks get larger with each edition but they fail to clarify the underlying mechanisms and processes of chemical reactivity.
  • The division of academic chemistry into organic and inorganic sub-disciplines is anachronistic and confusing.

I am concerned about how this effects professional scientists who are not chemists but who require a knowledge of chemistry, rather than professional chemists. A PhD chemist will have had many years of exposure to chemical science and will have gained a deep understanding of the subject. However, academic chemistry is a priesthood and the path-to-knowledge is not readily accessible to non-chemists. While this could be said about any profession, chemistry is uniquely inaccessible amongst the major sciences:

How many popular science books are there on: mathematics, complexity theory, cosmology, quantum physics, DNA, plate tectonics, evolution, computers... and how many are there about chemical reactivity?

How many chemical reactivity articles are there in New Scientist, Discovery or Scientific American?

At present, chemical reaction pedagogy – how we teach the subject – involves exposing students to chemical interactions and reactions until they understand.

I asked the members of the excellent chemistry education discussion list (ChemEd-L) "what is the simplest reaction mechanism or process you teach your students?" The most common answer was "SN2 nucleophilic substitution", exactly the example I had expected and certainly the one I was first taught at university.

So, we introduce our students to really quite involved reactions and reaction mechanisms and we explain how these example reactions proceed. It is hoped that with experience our students "will understand". Well, yes they will... once they have been immersed long enough... to receive their PhDs. This approach – in my humble opinion – leaves physicists, biologists, geologists, material scientists, medics, chemical engineers... largely in the dark about what it is that constitutes chemical reactivity.

Ralph Pearson's Hard Soft Acid Base (HSAB) principle – very unfortunately – compounded the problem. In the 1960s there was huge optimism about understanding chemical reaction science due the development of new ideas and theories:

  • FMO theory
  • Woodward-Hoffmann explanation of pericyclic reactivity
  • Klopman-Hudson theory
  • Pearson's HSAB principle
  • The growing utility of quantum chemistry techniques
  • Parameterisation of VSEPR theory into molecular mechanics software
  • etc., etc., (here).

These advances led to a "problem solved" attitude, and textbooks enthusiastically included the new material, particularly Pearson's HSAB principle which so naturally followed on from Lewis theory, valence bond (VB) theory and the valence shell electron pair repulsion (VSEPR) technique. Nearly all advanced inorganic and organic textbooks of the '70s and 80's had sections on hard and soft [Lewis] acids and bases... but now the topic is hardly mentioned at all.

As shown here, Pearson's HSAB principle is limited by the fact that no physical parameter correlates with hardness across Pearson's chosen sets of species. As a consequence, the HSAB analysis is ambiguous and limited. Indeed, the failure of the over-simple and over-hyped HSAB principle has meant that theoretical chemists have not looked at this important area of physical science since the late nineteen sixties.

What Is The Solution?

I hold that part of the solution to understanding chemical reactions and chemical reactivity involves the analysis presented in this web book. Recall the "chemistry tree graphic" that our story started with:

Chemogenesis tells the step-by-step story of how structure, reactivity and mechanism emerge from the periodic table of the elements. The story logically proceeds through structure, bonding & material type, hydrogen probe experiments, congeneric series, the five reaction chemistries, the Lewis acid/base interaction matrix, and an analysis of chemical science in terms of systems theory.


Without chemogenesis, it is necessary to learn about chemical reactions and chemical reactivity by the accumulation and assimilation of facts.

With chemogenesis, sense is made of a morass of chemical reaction information and the structure of reaction chemistry space logically emerges from physics, complexity and all.


Mark R. Leach


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© Mark R. Leach 1999-

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