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Chemical Bonding: the Journey from Miniature Hooks to Density Functional Theory

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Chemical Bonding: the Journey from Miniature Hooks to Density Functional Theory molecules Review Chemical Bonding: The Journey from Miniature Hooks to Density Functional Theory Edwin C. Constable * and Catherine E. Housecroft Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 24a, CH-4058 Basel, Switzerland; [email protected] * Correspondence: [email protected]; Tel.: +41-61-207-1001 Academic Editor: Antonio J. Mota Received: 10 May 2020; Accepted: 3 June 2020; Published: 5 June 2020 Abstract: Our modern understanding of chemistry is predicated upon bonding interactions between atoms and ions resulting in the assembly of all of the forms of matter that we encounter in our daily life. It was not always so. This review article traces the development of our understanding of bonding from prehistory, through the debates in the 19th century C.E. bearing on valence, to modern quantum chemical models and beyond. Keywords: bonding; valency; affinity, structure; history of science 1. Introduction Bonding is what separates chemistry from physics. If the understanding of atoms and their component particles belongs primarily to the realm of physics, then chemistry is concerned with the aggregation of atoms into chemical entities held together by bonds. If science is a language, and atoms are the letters, bonding is the mechanism by which the letters are combined into words. The International Union of Pure and Applied Chemistry (IUPAC) states that “there is a chemical bond between two atoms or groups of atoms in the case that the forces acting between them are such as to lead to the formation of an aggregate with sufficient stability to make it convenient for the chemist to consider it as an independent ‘molecular species’” [1]. Although the concept of bonding is inherent in the discipline of chemistry and its distinction from its neighbor, physics, our modern understanding of bonding is relatively recent. In the 19th century C.E., as chemists were making enormous advances in the methods for the preparation, purification, and characterization of new molecular species, they were in parallel struggling with developing models for understanding the structure and constitution of these compounds. However, the ideas and concepts did not spring fully-formed into the minds of the 19th century scientists, but can rather be traced as far back as when mankind started to think about matter and its components. This article attempts to give an overview of how we made this journey of discovery and will attempt to demonstrate how the concepts that are today so fundamental that we do not even think about them, proved troublesome and time-consuming to our forebears. This article is concerned primarily about the roots and origins of our understanding of bonding. Accordingly, it concentrates upon the introduction of new ideas and the controversies and changes that resulted rather than providing a full history of their development after acceptance. The reader is referred to modern texts on bonding [2–5], in particular the three-volume work by Mike Mingos celebrating the centennial of the chemical bond [6–8]. As always, we are indebted to those historians of science who have trodden this path before us in such an able and comprehensive manner [9–13]. A final note concerns the abbreviations of journals; over the years, many journals have changed their titles, some with a confusing and monotonous regularity. For consistency, the CASSI (CAS Source Index) abbreviations are used throughout. In those cases where a journal has changed Molecules 2020, 25, 2623; doi:10.3390/molecules25112623 www.mdpi.com/journal/molecules Molecules 2020, 25, 2623 2 of 44 Molecules 2019Molecules, 24, x FOR 2019 PEER, 24, x REVIEW FOR PEER REVIEW 2 of 46 2 of 46 primary abbreviationtitle,primary the abbreviation primary is used, abbreviation evenis used, though even is used, the though original even the though journaloriginal the title originaljournal may title journaldiffer may slightly. title differ may Asslightly. di anffer slightly. As an example, Astheexample, anabbreviation example the abbreviation, the Ann. abbreviation Phys. Ann. (Berlin, Phys.Ann. Ger.) (Berlin, Phys. is used (Berlin, Ger.) for is Ger.) theused entireis for used theperiod for entire the 1819 entireperiod to date, period 1819 even to 1819 date, to even date, though theeventhough contemporaryMolecules though the contemporary 2019 the, 24title contemporary, x FOR varied PEER title amongstREVIEW varied title Annalen variedamongst amongst der Annalen PhysikAnnalen derund Physik Physikalischen der und Physik Physikalischen undChemie Physikalischen, Annalen Chemie2 ,of Annalen Chemie46 , der Physik Annalenderund Physik Chemie der und,Physik Drude Chemie’ unds An, Drude Chemienalen’,s ,Poggendorff AnDrude’snalen, AnnalenPoggendorff’s Annalen, Poggendor’ sder Annalen Physikff’s , Annalender Annalen Physik der der, Annalen Physik Physik, Annalender(Leipzig, Physik der (Leipzig, Physik primary abbreviation is used, even though the original journal title may differ slightly. 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Liebigsder Annalen Physik und der Chemie Chemie, Drude und Pharmacie’s Annalen., Poggendorff After that’ bibliometrics Annalen der Physik aside,, letAnnalen the journey der Physik begin! (Leipzig, Germany) or Annalen der Physik (Weinheim, Germany); similarly, the abbreviation Justus Liebigs Ann. 2. Early Ideas2. Early up toIdeas the Ageup to of the Reason Age of Reason 2. EarlyChem. Ideas is used up for to theJustus Age Liebigs of Reason Annalen der Chemie, Annalen der Chemie und Pharmacie and Justus Liebigs This sectionThisAnnalen looks section der at Chemie the looks genesis und at Pharmacie the of genesis atomism. After of that atomismandatomism bibliometric investigates and aside, investigates the let then the journey contemporary the then begin! contemporary ideas ideas regarding regardingthe intera thections interactionsintera betweenctions atoms between that atoms resulted that in resulted matter inpossessing matter possessing distinct and distinct unique and unique 2. Early Ideas up to the Age of Reason properties.properties. The primary The focus primaryprimary of this focusfocus review ofof thisthis is review onreview bonding, is is on on bonding, butbonding, to comprehend but but to to comprehend comprehend how modern how how modernviews modern views views of of bondingbondingof evolved,bonding evolved,This weevolved, section need we needlooksawe broad need aat broad theoverview a genesisbroad overview overviewof atomismhow of how our of ourand understandinghow understanding investigates our understanding the of of thenatoms, atoms, contemporary ofwhich atoms, areare which ultimatelyideas are regarding the interactions between atoms that resulted in matter possessing distinct and unique ultimatelytheultimately the objects objects the that that objects are are connected connected that are byconnected by the the bonds, bonds, by developed.the developed. bonds, developed. It It is is convenient convenient It is convenient and and conventional conventional and conventional to start this properties. The primary focus of this review is on bonding, but to comprehend how modern views to start thisdiscussionto discussion start thiswith discussion with the the philosophies philosophies with the philosophies developed developed by developed by the the Early Early by Greek Greekthe Early civilization, civilization, Greek civilization, although although this thisalthough approach this is of bonding evolved, we need a broad overview of how our understanding of atoms, which are approach approachis neither chronologicallyis neither chronologically nor histor icallynor histor strictlyically correct. strictly correct. neitherultimately chronologically the objects nor that historically are connected strictly by the correct. bonds, developed. It is convenient and conventional to start this discussion with the philosophies developed by the Early Greek civilization, although this 2.1. The Greeks2.1. The Had Greeks a Word Had for aI tW Word ord for ItIt approach is neither chronologically nor historically strictly correct. The word Theatom word (and atom related (and terms related such terms as atomic, such asatomistic atomic,, atomistic,atomisticand atomism), and atomism)is derived isfrom derived the from the 2.1. The Greeks Had a Word for It Greek wordGreek: ἄτομος word:word (atomos): ἄτομοςτoµo& meaning(atomos) indivisible meaning indivisible or uncuttable. or uncuttable.uncuttable. Most histories Most Most ofhistories atomism of begin atomism begin with the Greekwith thephilosopher GreekThe word philosopher atomLeucippus (and related Leucippus
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