Table of chemical elements

Fig. 2.2. The periodic table of chemical elements, displayed in the modem long form. Each element is denoted by its symbol. From U (element atomic number 92) the elements have been...

Unknown 1. Try to identify a compound with the spectrum represented in Fig. 5.1. The exact molecular mass of the compound is 60.0211 Da, which defines its elemental composition as C2H4O2. At this stage pay attention only to the most abundant peaks in the spectrum m/z 60 (molecular ion) and primary fragment ions of m/z 45, m/z 43, m/z 28, and m/z 15. Use the masses of elements from the periodic table of chemical elements. 

Prior to the proposal of the Periodic Table, there was no information available on how many chemical elements could possibly exist. Even after the appearance of the numerous periodic tables of chemical elements, the rare earth elements were an especially difficult case because they could not be properly arranged into any of the Tables. Until the twentieth century, fractional crystallization was the only method of purification of elements. In most cases, this required thousands of recrystallizations involving months of work. As a result, there is a long list of various false claims among the rare earth elements, some of which are detailed below. 

Let s take a more detailed look at the periodic table and discover its great symmetry and usefulness. (Refer to the periodic table of chemical elements reproduced on the inside front and back covers of this book.)... 

In summary, the structure and recurring characteristics of elements are represented in the catalog-like periodic table of chemical elements. A review of the material covered thus far follows ... 

Period 5 (group 3 [IIIB] to group 12 [IIB]) is located in the second row of the transition elements and represents 10 of the transition metals to nonmetals found in the periodical table of chemical elements. This period is also known to include some of the so-called rare-earth elements. Most of the rare-earths are found in the lanthanide series, which follows barium (period 6, group 3). (Check the periodic table to locate the major rare-earth elements in the lanthanide series. These are addressed in a later section of the book.)... 

The halogens are the family of nonmetal elements in group 17 (VIIA) that are located just to the right of the oxygen group 16 on the periodic table of chemical elements. They are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). 

Some expanded periodic tables of chemical elements have been developed that include future elements up to the proton number 152 or 202. Someday the existence of new heavy elements may be realized if the United States once again takes the lead in particle physics and related research. 

The number of chemical elements has now reached 109, and the list is growing. Fortunately for students, only about 40 are relevant to basic chemistry. Please take a reconnaissance glance at the periodic table of chemical elements (found at the end of this chapter) and find calcium, element number 20. You need to be acquainted with the symbol and general properties of the 20 simplest elements up to calcium, plus another 20 of chemical significance that you will encounter in this book. 

Even the development of Mendeleyev s periodic table of chemical elements did not grant researchers the ability to plan and design new materials. Although Mendeleyev correctly predicted the existence of a few new elements, the number of compounds that can be made from elements is extremely vast and complex. Chemical Abstracts Service, a division of the American Chemical Society, maintains a registry of known substances. As of May 2009, there are about 47 million substances in this registry, and roughly 4,000 new substances are added every day. 

Dalton s table of chemical elements is the first in which chemical atoms and chemical elements appear in a one-to-one correspondence. Chemical elements for Dalton, as for Lavoisier, were substances that could not be decomposed into simpler substances. But Dalton went beyond Lavoisier, claiming that each chemical element was made up of identical and indivisible atoms, which were the element s smallest parts. Chemical elements were distinguished from one another by their chemical qualities and also by the different weights of their constituent atoms. Dalton did not claim to know the absolute weights of atoms, but made claims about their rel-ative weights. 

Because of these longer periods, not all of the main block elements were grouped together (e.g., F and Cl were separated from Br and I). Mendeleev therefore had to pursue the secondary classification and the longer periods were cut in half. By partitioning the Mendeleev line before Cu, Ag, and Au, Mendeleev obtained a modified periodic table of chemical elements (Figure 7). 

Atkins, P.W. (1997). ThePeriodicKingdom A Journey into the Land of the Chemical Elements, Basic Books, New York. A metaphorical description of the periodic table of chemical elements. Appropriate for any level of scientific background. 

WebQC.com. Periodic Table of Chemical Elements. http //www.webqc.org/ periodictable.php (accessed February 9, 2010). 

Characterize the essential trace elements and describe their position in the periodic table of chemical elements. 

Emphasis has been put in this chapter so far on the descriptive function of science with perhaps too little discussion of its predictive function. This latter function has been invaluable to the development of science. For example, Mendeleev left gaps in the Periodic Table of Chemical Elements. These were subsequently filled in by the discoveries of other researchers. As was mentioned in Chapter 1, engineering needs to use science in this predictive function but there is a crucial difference between prediction in science and prediction in engineering. The consequences of an incorrect prediction are quite different. It was very satisfying, no doubt, to discover new elements which fitted nicely into... 

The path of discovery of the elements belonging to the group termed rare earth elements was particularly confused and chaotic. It started 200 years ago, in 1787, and it closed in 1947 with the discovery of promethium. The rare earth elements cannot be properly and decently arranged in any of the numerous periodic tables of chemical elements developed since Mendeleev and Meyer, and though the modern... 

Mendeleev, Dmitri Ivanovich (1834-1907) Russian chemist. Mendeleev is remembered for developing the periodic table of chemical elements in a classic paper published in 1869 entitled On the Relation of the Properties to the Atomic Weights of Elements. Other scientists such as Julius Lothar Meyer and John Newlands had similar ideas at about the same time but Mendeleev developed his ideas much more fully, including the predictions of the existence and properties of hitherto unknown elements such as gallium, scan-... 

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