DEVELOPMENT OF THE PERIODIC TABLE

In summary, quantum theory s more sophisticated treatment of electrons allows us to more accurately describe the positions of electrons around a given nucleus. This can help us understand chemical bonding in a more detailed way. 

the periodic law and the periodic table were bom, although only 63 elements had been discovered by 1869 (for example, the noble gases were not discovered until after 1893), and the clarifying concept of the atomic number was not known until 1913. Mendeleev s idea and textbook achieved great success, and he rose to a position of prestige and fame while he continued to teach at the University of St. Petersburg. 

The empty spaces in the table and Mendeleev s predictions of the properties of missing elements stimulated a flurry of prospecting for elements in the 1870s and 1880s and eight more were discovered by 1886. 

Mendeleev found that a few elements did not fit under other elements with similar chemical properties when arranged according to increasing atomic 

Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Beitelhnn Californium Einstmnhim Fennhim Mendderinn NbbAim I wimnaim  

Today s periodie table, which appears on the inside front cover of the text, resembles Mendeleev s in most details, although it includes 49 (and still counting) elements that were unknown in 1870. The only substantive change is that the elements are now arranged in order of atomic number (number of protons) rather than atomie mass. 

The discovery of chemical elements has been ongoing since ancient times (T FIGURE 7.1). Certain elements, such as gold (Au), appear in nature in elemental form and were thus discovered thousands of years ago. In contrast, some elements, such as technetium (Tc), are radioactive and intrinsically unstable. We know about them only because of technology developed during the twentieth century. 

The majority of elements readily form compounds and, consequently, are not found in nature in their elemental form. For centuries, therefore, scientists were unaware of their existence. During the early nineteenth century, advances in chemistry made it easier to isolate elements from their compounds. As a result, the number of known elements more than doubled from 31 in 1800 to 63 by 1865. 

Which row of the periodic table contains the most recently discovered elements Can you suggest a reason  

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As the field of chemistry developed, so did the interest in the chemistry of soil. This was natural because the early chemists extracted elements from geological sources and, in the broadest sense, from soil itself. In fact, the development of the periodic table required the extraction, isolation, and identification of all of the elements, many of which are found abundantly in soil. 

One cannot go further into the development of the periodic table beyond this point, because one soon comes to the end of the series of known elements. However, it appears fairly certain that the elements following uranium have some resemblance to actinium, which means that this element marks the beginning of a second series of rare earths, the actinides. 

Development of the Periodic Table Group 0 - the noble gases... 

The systemization of chemistry was also well underway, propelled in large part by Mendeleev s development of the Periodic Table in 1869. Two postulates and an enormous number of careful experimental measurements played a crucial role in this work ... 

There is nothing like the development of the periodic table through time to give one a sense of the pace of chemical discovery. Lavoisier listed close to thirty elements, and this number more than doubled when Mendeleev invented the periodic table. Since then, we have added the lanthanides and actinides, as well as a stream of artificial radioactive elements. 

To repeat the thought processes of Mendeleyev and Meyer in the development of the periodic table... 

Section 3.1 takes up the experimental laws on which Dalton based his atomic theory, and Section 3.2 discusses that theory itself. Some modern extensions of the theory, including subatomic particles and isotopes, are presented in Section 3.3. The concept of the masses of atoms of the individual elements is presented in Section 3.4, and the development of the periodic table is traced in Section 3.5. A much more sophisticated theory of the atom will be presented in Chapter 4. 

Many atomic masses were determined as a direct result of Dalton s postulates and the work that they stimulated, and scientists attempted to relate the atomic masses of the elements to the elements properties. This work culminated in the development of the periodic table by Dmitri Mendeleyev (1834-1907) (Figure 3.8) and independently by Lothar Meyer (1830-1895). Because Mendeleyev did more with his periodic table, he is often given sole credit for its development. 

One of the most striking things about the chemistry of the elements is the periodic repetition of properties. There are several groups of elements that show great similarities in chemical behavior. As we saw in Chapter 2, these similarities led to the development of the periodic table of the elements. In this chapter we will see that the modern theory of atomic structure accounts for periodicity in terms of the electron arrangements in atoms. 

Stwertka, Albert. A Guide to the Elements, 2nd ed. New York Oxford University Press, 2002. This book explains some of the basic concepts of chemistry and traces the history and development of the periodic table of the elements in clear, nontechnical language. 

The development of the periodic table and concept of electron configuration gave chemists a rationale for molecule and compound formation. This explanation, formulated by Gilbert Lewis, is that atoms combine in order to achieve a more stable electron configuration. Maximum stability results when an atom is isoelectronic with a noble gas. 

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