Lewis spent 25 years determining free energies of various substances. Lewis was the first to produce a pure sample of deuterium oxide heavy water in and the first to study survival and growth of life forms in heavy water. By accelerating deuterons in Ernest O. Lawrence's cyclotron, he was able to study many of the properties of atomic nuclei. In , by studying the magnetic properties of solutions of oxygen in liquid nitrogen, he found that O4 molecules were formed.
This was the first evidence for tetratomic oxygen. In , Lewis was the first to propose an empirical equation describing the failure of strong electrolytes to obey the law of mass action, a problem that had perplexed physical chemists for twenty years.
His empirical equations for what he called ionic strength were later confirmed to be in accord with the Debye-Huckel equation for strong electrolytes. In , he coined the term "photon" for the smallest unit of radiant energy light. To contact the author mail: articles worldofchemicals.
Stay updated with the latest chemical industry trends and innovations. Verification Code has been sent to. Please enter the Verification Code below to verify your Email Address. Based on criteria derived from this reconstruction, Niaz evaluated general chemistry textbooks published in U.
Research in science education has recognized not only the importance of history and philosophy of science but also its implications for textbooks Abd-El-Khalick et al. The main objectives of this study are: 1 development of a perspective based on history and philosophy of science HPS considerations in order to understand the postulation of the covalent shared pair bond by Lewis; 2 formulation of criteria based on the HPS perspective that could be useful in the evaluation of general chemistry textbooks; and 3 evaluation of general chemistry textbooks published in Turkey utilizing the criteria based on the HPS perspective.
This study is based on the same criteria that were used by Niaz to evaluate general chemistry textbooks published in U. A History and Philosophy of Science Perspective. Lewis is generally considered to have presented the first satisfactory model of the covalent shared pair bond based on the cubic atom in It is important to note that the genesis of the cubic atom can be traced to an unpublished memorandum written by Lewis in and recounted by him in the following terms:.
In the year while I was attempting to explain to an elementary class in chemistry some of the ideas involved in the periodic law becoming interested in the new theory of the electron Thomson's discovery of the electron in , and combining this idea with those which are implied in the periodic classification, I formed an idea of the inner structure of the atom model of the cubic atom which, although it contained crudities, I have ever since regarded as representing essentially the arrangement of the electrons in the atom.
Lewis, , pp. Lewis reproduced the postulates of his theory of the cubical atom at length, of which the third postulate stated: "The atom tends to hold an even number of electrons in the shell, and especially to hold eight electrons which are normally arranged symmetrically at the eight corners of a cube" p. This postulate was the most striking and at the same time controversial feature of Lewis's theory, which led to the formulation of the 'rule of eight' or the 'octet rule. Thus the single bond was conceived of as two cubic atoms with a shared edge pair of electrons and the double bond as two cubes with a common face.
Lewis's model of the covalent bond in retrospect. In this section evidence is provided to show that Lewis's theory of sharing electrons covalent bond had to compete with a rival theory, viz.
According to Lakatos : " The history of science has been and should be a history of competing research programmes According to Kohler , who has presented a detailed account of the origin of Lewis's ideas:.
When it was first proposed, Lewis's theory was completely out of tune with established belief. For nearly 20 years it had been almost universally believed that all bonds were formed by the complete transfer of one electron from one atom to another.
From the standpoint of the polar theory the idea that two negative electrons could attract each other of that two atoms could share electrons was absurd p. Rodebush , a chemist reviewing the origin of the covalent bond in the late s, shared the same concern:.
Since according to Coulomb's law two electrons should exert a repulsion for each other, the pairing of electrons seems at first glance to be a bizarre idea. In order to account for the peculiar behavior Lewis assumed the existence of a magnetic attraction between the electrons pp. Lewis further clarified his attempt at building a theory of the atom: "In my original theory [] I considered the elements in the periodic table thus built up, as if block by block, forming concentric cubes" p.
Later in the article Lewis recognizes that the cubic structure cannot represent the triple bond and suggests its replacement by the tetrahedral atom p. At this stage it is important to note that Thomson's discovery of the electron in and later publications Thomson, provided powerful arguments for the polar theory of the ionic bond.
According to Thomson : "For each valency bond established between two atoms the transference of one corpuscle from the one atom to the other has taken place Although Thomson accepted that overlapping of corpuscles could produce a nonpolar bond in theory, he believed that in reality all bonds were polar bonds p.
Material presented in this section has been adapted from Niaz Based on the historical perspective rational reconstruction presented by Niaz , here we present criteria for the evaluation of Turkish general chemistry textbooks see Appendix 1. Criterion 1. Lewis's cubic atom as a theoretical device for understanding the sharing of electrons : Lewis's cubic atom was based on his atomic theory based on postulates formulated in The cubic atom was thus a theoretical device that was later used for understanding the sharing of electrons covalent bond and provided the rationale for the octet rule.
This criterion is based on the following references: Lewis ; , Kohler and Jensen Following classifications were elaborated:. Satisfactory S : treatment of the subject in the textbook is considered to be satisfactory if it is briefly explained that Lewis used his model of the cubic atom to explain the sharing of electrons and the octet rule.
Mention M : a simple mention of Lewis's cubic atom. No-mention N : no-mention of Lewis's cubic atom. Criterion 2.
The origin of the polar bond as the dominant paradigm in chemical combination can be traced to Thomson's discovery of the electron in By the polar theory completely dominated chemistry, and it was in the early s that Lewis's idea of sharing electrons became acceptable. This criterion is based on the following references: Thomson ; and , Lewis ; , Lakatos and Kohler Mention M : a simple mention of the competing frameworks. No-mention N : no-mention of the competing frameworks. Criterion 3.
Inductivist I : Lewis's covalent bond was an inductive generalization based on: stability of the noble gases or formation of the hydrogen molecule leads to a lowering of the energy or Helium an inert gas has a pair of electrons or numbers of electrons in most compounds are even. Lakatosian L : Lewis's shared pair covalent bond was not induced from experimental evidence but derived from the cubic atom.
No-mention N : textbook makes no-mention explicitly to either of the two interpretations, presented above. Criterion 4. Pauli Exclusion Principle as an explanation of the sharing of electrons in covalent bonds : the objective of this criterion is to evaluate if textbooks consider Pauli's exclusion principle to provide an explanation of the sharing of electrons.
This criterion is based on the following references: Pauli , Rodebush , Lakatos and Kohler Satisfactory S : treatment of the subject in the textbook is considered to be satisfactory if the role of Pauli Exclusion Principle is briefly described, in order to explain the covalent bond. Their work was of immense value in predicting whether reactions will go almost to completion, reach an equilibrium, or proceed almost not at all, and whether a mixture of chemicals can be separated by distillation.
Lewis was educated at home, while his family lived in Massachusetts and Nebraska, until he was 14 years old. His subsequent education was more conventional, although nonetheless stimulating, and included a doctorate from Harvard University earned under Theodore W. Lewis then made the pilgrimage to Germany to work with the physical chemists Walther Nernst and Wilhelm Ostwald. He held several university faculty appointments, including ones at the Massachusetts Institute of Technology and the University of California, Berkeley, where he expanded the programs in chemistry and chemical engineering.
Lewis was nominated 35 times for a Nobel Prize but never won. This creates dipoles in each H-O bond, and these dipoles do not cancel each other out, leaving the water molecule polar overall Figure 7. Read more about these bonds in our module Properties of Liquids. When the electrons in a bond are perfectly shared, there is no dipole , and neither end of the bond carries any partial charge. When no such overall charge exists, the molecule is said to be non-polar.
An example of such a non-polar molecule is hydrogen, H 2. In larger molecules with multiple covalent bonds , each bond will have either no dipole or a dipole with varying degrees of partial charge. When all of these dipoles are taken into consideration in three dimensions, the uneven distribution of charge caused by the dipoles may cancel out, making the molecule non-polar.
Alternatively, there may be a partial electrical charge across the molecule , making it a polar molecule. An example of a multiple atom non-polar molecule is carbon dioxide.
We have limited our discussion to ionic and covalent bonding and the sliding scale of bond type that exists between them. However, many other types of interactions and bonds between atoms exist, notably metallic bonding the attractions that hold metal atoms together in metallic elements , and intermolecular forces the interactions that exist between, rather than within, covalently bonded molecules.
These each involve similar electrostatic interactions to the ones described in ionic and covalent bonds , but even those extensions are far from the end of the bonding story.
In , researchers found the first experimental evidence for a new type of interaction between atoms that had been predicted in the s Fleming et al. Named a "vibrational bond," the theory describes a lightweight element in this case, an isotope of hydrogen oscillating or "bouncing" between two much heavier atoms in this case, bromine and effectively holding the larger atoms together.
Donald Fleming, a chemist based at the University of British Columbia in Canada, described the new bond as being "like a Ping Pong ball bouncing between two bowling balls.
The millions of different chemical compounds that make up everything on Earth are composed of elements that bond together in different ways. This module explores two common types of chemical bonds: covalent and ionic. The module presents chemical bonding on a sliding scale from pure covalent to pure ionic, depending on differences in the electronegativity of the bonding atoms.
When a force holds atoms together long enough to create a stable, independent entity, that force can be described as a chemical bond. The known chemical elements interact with one another via chemical bonds, to create brand new, unique compounds that have entirely different chemical and physical properties than the elements that make them up.
It is helpful to think of chemical bonding as being on a sliding scale, where at one extreme there is pure covalent bonding, and at the other there is pure ionic bonding. Most chemical bonds lie somewhere between those two extremes. When a chemical bond is formed between two elements, the differences in the electronegativity of the atoms determine where on the sliding scale the bond falls.
Large differences in electronegativity favor ionic bonds, no difference creates non-polar covalent bonds, and relatively small differences cause the formation of polar-covalent bonds. Reading Quiz Resources Table of contents The history of the chemical bond The modern chemical bond Types of chemical bonds Covalent bonding Multiple covalent bonds Ions and ionic bonding Lewis dot diagrams When is it ionic? When is it covalent? How covalent is covalent? Polarity and dipoles in covalent molecules Other types of bonding and the future Terms you should know electrostatic : relating to the forces of attraction or repulsion between particles based on their electrical charges.
Figure 1 : Life on Earth depends on water, not only for key biological functions but also for pleasure. Comprehension Checkpoint Lewis based his theory of bonding on a.
0コメント