Order in the elements

Most of the chemistry in this book revolves around elements and isotopes (see Box 1.1). It is therefore helpful to understand how the atomic number (Z) of an 

Although the periodic pattern becomes more complicated above Z values of 20, the overall ordering persists. Complications arise in the so-called transition elements that occupy a position between columns II and HI of the Periodic Table (Fig. 2.2). These elements have between one and three valence electrons. Importantly, however, the electrons in the orbital below the valence electrons have almost the same energy as the valence electrons themselves. In some compounds, 

There have been many attempts to further classify the elements geologically and environmentally. In Fig. 2.3 we show the most abundant elements in four of the main environmental materials of the Earth. A glance at this figure shows that 

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It was Mendeleev who discovered the periodic law, a principle that describes the periodicities that are observed in the properties of the chemical elements. This enabled him to predict the existence of as-yet-undiscovered elements, to predict their atomic weights, and to describe their chemical and physical properties as well. It was Mendeleev who found the natural order in the elements that his predecessors Newlands, Chancourtis, and Odling had been seeking. Mendeleev couldn t explain why there were so many elements he didn t even try to do that. But he did discover the existence of striking patterns. 

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