Thermodynamics

Periodic Table

This is the start of the WebElements periodic table documentation

Cubic nitrogen with single N-N bonds

Single-bonded cubic form of nitrogenSingle-bonded cubic form of nitrogenEveryone knows that elemental nitrogen exists in the atmosphere as dinitrogen, N2. There is a triple bond between the two nitrogen atoms. This is true - but under certain conditions, a fascinating N-N single bonded phase has been characterized.1

In 1985 it was predicted that at high pressure, nitrogen would transform to a solid with a single-bonded crystalline structure called polymeric nitrogen. Later, it was proposed that it whould have a cubic gauche (cg-N) structure. Experimental evidence was scant however until 2004 when a team of scientists from Germany and Russia managed to make the compound directly from molecular nitrogen at temperatures above 2000 K and pressures above 110 GPa using a laser-heated diamond cell. The material was characterized by X-ray and Raman scattering methods we have identified this as the polymeric nitrogen (cg-N).

The phase is a stiff with a bulk modulus ≥300 GPa. This is characteristic of strong covalent solids. The polymeric nitrogen is metastable. The structure of N is polymeric with each nitrogen bound to three other nitrogen atoms. At a pressure of 115 GPa, each N-N bond length is 1.346 ± 0.004 Å. The N-N-N angles are all about 108.8°, very close to the ideal tetrahedral angle of just over 109°.

It did not prove possible to recover the polymeric nitrogen by releasing the pressure - in other words the polymer reverts to normal dinitrogen. The authors speculate that this form of nitrogen is a new class of single-bonded nitrogen materials that may have unique energy capacity properties (more than five times that of the most powerful energetic materials).

New Periodic Table book by Eric Scerri

It's great to see a new book about the periodic table and this one is written by Eric Scerri, a world authority on the periodic table! Dr. Eric Scerri is a leading philosopher of science specializing in the history and philosophy of the periodic table. He is also the founder and editor in chief of the international journal Foundations of Chemistry and is a full-time lecturer at UCLA where he regularly teaches classes of 350 chemistry students as well as classes in history and philosophy of science. You can buy this book from our WebElements Amazon Store or our WebElements Amazon UK Store.

The Periodic Table: Its Story and Its Significance

The periodic table is one of the most potent icons in science. It lies at the core of chemistry and embodies the most fundamental principles of the field. The one definitive text on the development of the periodic table by van Spronsen (1969), has been out of print for a considerable time. The present book provides a successor to van Spronsen, but goes further in giving an evaluation of the extent to which modern physics has, or has not, explained the periodic system. The book is written in a lively style to appeal to experts and interested lay-persons alike.

The Periodic Table begins with an overview of the importance of the periodic table and of the elements and it examines the manner in which the term 'element' has been interpreted by chemists and philosophers. The book then turns to a systematic account of the early developments that led to the classification of the elements including the work of Lavoisier, Boyle and Dalton and Cannizzaro. The precursors to the periodic system, like Döbereiner and Gmelin, are discussed. In chapter 3 the discovery of the periodic system by six independent scientists is examined in detail.

Two chapters are devoted to the discoveries of Mendeleev, the leading discoverer, including his predictions of new elements and his accommodation of already existing elements. Chapters 6 and 7 consider the impact of physics including the discoveries of radioactivity and isotopy and successive theories of the electron including Bohr's quantum theoretical approach. Chapter 8 discusses the response to the new physical theories by chemists such as Lewis and Bury who were able to draw on detailed chemical knowledge to correct some of the early electronic configurations published by Bohr and others.

Chapter 9 provides a critical analysis of the extent to which modern quantum mechanics is, or is not, able to explain the periodic system from first principles. Finally, chapter 10 considers the way that the elements evolved following the Big Bang and in the interior of stars. The book closes with an examination of further chemical aspects including lesser known trends within the periodic system such as the knight's move relationship and secondary periodicity, as well at attempts to explain such trends.

WebElements: the periodic table on the WWW [http://www.webelements.com/]

Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.