Lewis/Kossel model

Historical Development of the Lewis/Kossel Model 2.1 The Periodic Table... 

Extensions of the Lewis/Kossel Model 3.1 Generalisations of the Lewis Structures... 

The Kossel-Lewis-Langmuir model for chemical bonding recognized covalent bonds in which electrons are shared to form complete octets for each of two bonded atoms. The model classified highly polar compounds as those in which electrons are transferred from one atom to another to form ions. It was obvious even then that there are gradations of polarity with resulting chemical and physical consequences. 

The discussion above has indicated some of the limitations of the original Lewis/ Kossel descriptiOTi of chemical bonding and the manner in which it has been adapted to assimilate the multitude of new compounds being reported from chemical laboratories during the last century. Central to the model is the definition of the chemical bond as a pair of electrons and the adherence to the octet rule. 

The Relevance of the ELF Topological Approach to the Lewis, Kossel, and Langmuir Bond Model... 

Why do we want to model molecules and chemical reactions Chemists are interested in the distribution of electrons around the nuclei, and how these electrons rearrange in a chemical reaction this is what chemistry is all about. Thomson tried to develop an electronic theory of valence in 1897. He was quickly followed by Lewis, Langmuir and Kossel, but their models all suffered from the same defect in that they tried to treat the electrons as classical point electric charges at rest. 

Chapter 1 discusses classical models up to and including Lewis s covalent bond model and Kossell s ionic bond model. It reviews ideas that are generally well known and are an important background for understanding later models and theories. Some of these models, particularly the Lewis model, are still in use today, and to appreciate later developments, their limitations need to be clearly and fully understood. 

Lewis and Kossel s proposals coincided with the shell structure of atoms which resulted firom the hybrid classical/quantum model for the hydrogen atom developed by Bohr [37, 38] and subsequently extended by Sommerfeld [39 1] to other atoms. They did not fully appreciate the physical imphcations of a quantum model. Specifically Lewis based his model on the following postulates ... 

Lewis and Kossel both suggested the electrons in molecules and ions form concentric groups of either two or eight electrons, although they represented them in quite different ways. Lewis preferred to represent them using a cubic model (his static representation of the electrons led to a symmetrical arrangement if they were located at the vertices of a cube), whereas Kossel preferred to use concentric rings to illustrate the successive shells. The different representations are summarised for neon in Fig. 1. 

Based on Sommerfeld s atomic model [11] of elliptic orbits, directed towards the corners of a cube, a number of chemists, including Kossel, Lewis, Langmuir and Bury, developed an electronic theory to account for atomic structure and valency at... 

---