Mendeleev and Meyer

A historical perspective on the development of the modern periodic table is both interesting and important. A Russian chemist by the name of Dimitri Mendeleev is generally credited with the development of the first periodic table, although a German chemist, Lothar Meyer, working independent of Mendeleev at approximately the same time, did much the same work. Their 

The physical properties that they observed included such basic properties as color and density the chemical properties they studied included the manner of reaction of an element with acid (e.g., no reaction, slow reaction, fast reaction, or violent reaction) and the formula of the compound formed between each element and chlorine. Their published results included the grouping of elements into families, each containing elements that exhibited similar properties. The result was a periodic table with periods and families that were remarkably similar to the modern periodic table. 

At that time, the fact that not all the elements had yet been discovered was unknown to Mendeleev and Meyer. Mendeleev s table has only 62 elements. However, due to the regular pattern he observed, Mendeleev made some bold predictions that as yet undiscovered elements would be discovered at some point in the future and would fill certain holes he observed in his table. He even went so far as to predict specific properties for these elements. For example, the element germanium was not known at that time. There was a space in Mendeleev s table between silicon and tin in Group IVA (or Group 14). Mendeleev not only predicted the discovery of an element to fill this space, but he even went on to predict specific properties this element would have. He named this element eka-silicon. Germanium was later discovered and was found to have properties nearly identical to what Mendeleev had predicted. 

The important lesson to be learned from this story is that the electron configurations of elements are closely related to the elements properties. The periodic table based on electron configurations is remarkably similar to the one based on properties. 

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This system of nomenclature has withstood the impact of later experimental discoveries and theoretical developments that have since the time of Guyton de Morveau and Lavoisier greatiy altered the character of chemical thought, eg, atomic theory (Dalton, 1802), the hydrogen theory of acids (Davy, 1809), the duahstic theory (Berzehus, 1811), polybasic acids (Liebig, 1834), Periodic Table (Mendeleev and Meyer, 1869), electrolytic dissociation theory (Arrhenius, 1887), and electronic theory and modem knowledge of molecular stmcture. 

In 1869 Mendeleev and Meyer independently proposed the periodic law. The periodic law states that when the elements are arranged in order of increasing atomic mass, certain sets of properties occur periodically. 

What were the periodic properties of the elements upon which Mendeleev and Meyer established their periodic table of the elements ... 

During the 50 years after the periodic tables of Mendeleev and Meyer were proposed, experimental advances came rapidly. Some of these discoveries are shown in Table 2-1. 

In 1869 both Mendeleev and Meyer, working separately, published nearly identical classification schemes for the elements that were the forerunners of the modem periodic table. Although scientists of that time had no knowledge of atomic numbers, both schemes ordered the elements in nearly correct order from lowest to highest atomic number. Which of the following is the most likely explanation ... 

Van Spronsen, Johannes W. (1969). The Priority Conflict between Mendeleev and Meyer. Journal of Chemical Education 46 136-139. 

Just as there are some typically chemical explanations, such as talk of electron orbitals, which are best pursued at an autonomous level of explanation, Scerri McIntyre (1997) suggest that there are also some irreducible chemical laws. A good example of such a chemical law is provided by the so called periodic law , as first discovered by Mendeleev and Meyer, but anticipated by many others. Viewed from the perspective of physics, the status of the periodic system may appear to be far from law-like. Significantly, the periodic law seems not to be exact in the same sense as are laws of physics, for instance Newton s laws of motion. Loosely expressed, the periodic law states that there exists a periodicity in the properties of the elements governed by certain intervals within their sequence arranged according to their atomic numbers. 

By the seventeenth century, the common strong acids— nitric, sulfuric, and hydrochloric—were known, and systematic descriptions of common salts and their reactions were being accumulated. As experimental techniques improved, the quantitative study of chemical reactions and the properties of gases became more common, atomic and molecular weights were determined more accurately, and the groundwork was laid for what later became the periodic table of the elements. By 1869, the concepts of atoms and molecules were well established, and it was possible for Mendeleev and Meyer to propose different forms of the periodic table. Figure 1.9 illustrates Mendeleev s original periodic table. ... 

INTRODUCTION AND SECTION 7.1 The periodic table was first developed by Mendeleev and Meyer on the basis of the similarity in chemical and physical properties exhibited by certain elements. Moseley established that each element has a unique atomic number, which added more order to the periodic table. We now recognize that elements in the same column of the periodic table have the same number of electrons in their valence orbitals. This similarity in valence electronic structure leads to the similarities among elements in the same... 

Although Mendeleev and Meyer came to essentially the same conclusion about the periodicity of elemental properties, Mendeleev is given credit for advancing his ideas more vigorously and stimulating new work. His insistence that elements with similar... 

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 and Meyer arranged the elements in tables so that elements with similar properties were in the same column or row. These were the first periodic tables of the elements. The arrangements were not perfect. For all elements to fall into the proper groups, it was necessary to switch a few of them in a way that interrupted the orderly increase in atomic masses. Of the two reasons for this, one was anticipated at that time There were errors in atomic weights (as they were known in 1869). The second reason was more important. About 50 years later, it was found that the correct ordering property is the atomic number, Z, rather than the atomic mass. 

There are many ways to classify a collection of objects. Different criteria satisfy different purposes. Mendeleev and Meyer arranged their periodic tables based on two criteria The atomic masses of the elements increased across a row and the chemical properties of the elements in a column were similar. Mendeleev is more famous than Meyer as the founder of the periodic table because he subsequently used his classification scheme to make predictions about unknown elements. His predictions were later found to be true. 

Think, for a moment, how remarkable this is. Mendeleev and Meyer developed their periodic tables from the physical and chemical properties of the elements. They knew nothing of electrons, protons, nuclei, wave functions, or quantized energy levels. Yet, when these things were found some 60 years later, the match between the first periodic tables and the quantum mechanical model of the atom was nearly perfect. 

Mendeleev and Meyer developed their periodic tables by trying to organize some recurring physical and chemical properties of the elements. Some of these properties are examined in this section. 

Early in the twentieth century, Henry Moseley refined the periodic table with the concept of the atomic number, thus resolving a few inconsistencies in the tables proposed by Mendeleev and Meyer. 

Starting with Mendeleev and Meyer, and continuing to the present, enough periodic tables have been published to fill a book. We shall examine the Mendeleev table of 1871 (Table 7.1) because some of its usages and conventions still persist. We shall then look at modem periodic tables. 

What specifically were the properties that Mendeleev and Meyer observed leading up to the development of their periodic tables What specific properties are we talking about when we say that elements in a given family have similar properties What specific descriptions can be given for elements within a family... 

The periodic table was invented independently by Mendeleev and Meyer. Both noticed that if the elements were listed in the order of increasing atomic mass, there was a repetition (periodicity) of chemical and physical properties. For example, lithium, sodium, potassium, rubidium, and cesium all form oxides with the formula M2O and chlorides... 

The priority dispute between Mendeleev and Meyer was one of several that Russian chemists had with foreign chemists in the years after the 1860s. These priority disputes stoked Russians feelings of nationalism, which were growing very strong at this time in many other aspects of Russian hfe. Even some Russians who did not particularly like Mendeleev appeared to defend him in this priority dispute. 

After 1871 Mendeleev and Meyer focused on other scientific problems. It was only in 1873 that Meyer published a paper on the system of inorganic chemistry in connection with discussions on atomicity resulting from a paper by Juhus Thomsen (1826-1909) on the basicity of Uberjodsaure (periodic acid). He used the system to make his argument. After 1878 Meyer pubhshed several papers on the determination of atomic weights. 

Apart from historical articles, Norwegian journals mainly addressed the periodic system in articles on radioactivity, and only some decades after the system had been published by Mendeleev and Meyer. The discovery of more than thirty new radioactive elements evidently became a puzzle to chemists before the concept of isotopy was introduced by Frederick Soddy (1877-1956) in 1913, chemists were worried about how to fit all the new elements into the periodic system. An instructor at the technical school in Christiania, Haavard Martinsen (1879-1967), conveyed this challenge in an article in Pharmacia, several years before many of the radioelements were recognized as isotopes of known chemical elements. Martinsen, who had spent the previous summer working in William Ramsay s laboratory in London, acknowledged the advantages of Mendeelev s periodic system. However, faced with the evidence that radioelements such as radium emit helium, chemists were, in Martinsen s opinion, left with two options Either to maintain the old established definition of the concept of element and according to this perceive radium and similar substances as common chemical compounds, or to throw the old definition overboard and admit the divisibility of the elements. ... 

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