Atomic structure periodic properties

The periodic table proposed by Mendeleev (1870) gives relationships between atomic structure and properties the concept of an internal structure of atoms and molecules becomes ever more relevant, and important studies are made such as those of G. N. Lewis [Lewis, 1916 Lewis, 1923]. 

Why are there repeatable patterns of properties across the periods in the periodic table Again, it is because there is a repeatable pattern in atomic structure, and properties depend on atomic structure. Each period begins with one valence electron for atoms of the elements in Group lA. Each period builds up to eight valence electrons, and the period ends. This pattern repeats across periods two through six. As more elements are made by nuclear accelerators (Section 13.6), it is possible that period seven will be completed someday. 

The development of the structural theory of the atom was the result of advances made by physics. In the 1920s, the physical chemist Langmuir (Nobel Prize in chemistry 1932) wrote, The problem of the structure of atoms has been attacked mainly by physicists who have given little consideration to the chemical properties which must be explained by a theory of atomic structure. The vast store of knowledge of chemical properties and relationship, such as summarized by the Periodic Table, should serve as a better foundation for a theory of atomic structure than the relativity meager experimental data along purely physical lines. ... 

To understand how the electron has been applied to explanations of the periodic table we must start with the discovery of the periodic system itself. The Russian chemist Dimitri Mendeleev announced in 1869 that the properties of elements arranged in order of increasing atomic weight appeared to repeat after certain definite intervals. Yet even as this discovery became increasingly well established, Mendeleev remained strongly opposed to any attempt to reduce or explain the periodicity in terms of atomic structure. He resisted the notion of any form of primary matter, which was actively discussed by his contemporaries, and opposed... 

What Are the Key Ideas The structures of atoms determine their properties consequently, the behavior of elements is related to their locations in the periodic table. 

What Do We Need to Know Already The information in this chapter is organized around the principles of atomic structure and specifically the periodic table (Chapter 1). However, the chapter draws on all the preceding chapters, because it uses those principles to account for the properties of the elements. 

For example, E. G. Mazurs (note 2, p. 105) expresses the discord as follows The periodicity of atomic structure must be accepted as a Natural Law. Therefore, scientists have to change their minds, get away from the conservatism that accepts only Mendeleev s chemical table as right, and adjust the other phenomena to this phenomenon that is, derive the chemical and physical properties of the elements from the electronic structure of the atoms. ... 

Comments on some trends and on the Divides in the Periodic Table. It is clear that, on the basis also of the atomic structure of the different elements, the subdivision of the Periodic Table in blocks and the consideration of its groups and periods are fundamental reference tools in the description and classification of the properties and behaviour of the elements and in the definition of typical trends in such characteristics. Well-known chemical examples are the valence-electron numbers, the oxidation states, the general reactivity, etc. As far as the intermetallic reactivity is concerned, these aspects will be examined in detail in the various paragraphs of Chapter 5 where, for the different groups of metals, the alloying behaviour, its trend and periodicity will be discussed. A few more particular trends and classification criteria, which are especially relevant in specific positions of the Periodic Table, will be summarized here. 

In 1920 Bohr turned his attention to the problem of atomic structure. Matters had become somewhat more complicated than they were in Mendeleev s day. By 1920, 14 elements had been discovered that did not seem to follow Mendeleev s periodic law. Called the rare earths, they had similar properties and followed one another in the table of elements they were elements 58 through 71. When Mendeleev formulated his law only two had been discovered, so they didn t seem to present any great problem. But now they presented an anomaly that no one had been able to clear up. A workable theory of atomic structure would have to explain not only why periodicities were seen in the larger part of the table of the elements but also why they disappeared when one came to the rare earths. 

Every example of a vibration we have introduced so far has dealt with a localized set of atoms, either as a gas-phase molecule or a molecule adsorbed on a surface. Hopefully, you have come to appreciate from the earlier chapters that one of the strengths of plane-wave DFT calculations is that they apply in a natural way to spatially extended materials such as bulk solids. The vibrational states that characterize bulk materials are called phonons. Like the normal modes of localized systems, phonons can be thought of as special solutions to the classical description of a vibrating set of atoms that can be used in linear combinations with other phonons to describe the vibrations resulting from any possible initial state of the atoms. Unlike normal modes in molecules, phonons are spatially delocalized and involve simultaneous vibrations in an infinite collection of atoms with well-defined spatial periodicity. While a molecule s normal modes are defined by a discrete set of vibrations, the phonons of a material are defined by a continuous spectrum of phonons with a continuous range of frequencies. A central quantity of interest when describing phonons is the number of phonons with a specified vibrational frequency, that is, the vibrational density of states. Just as molecular vibrations play a central role in describing molecular structure and properties, the phonon density of states is central to many physical properties of solids. This topic is covered in essentially all textbooks on solid-state physics—some of which are listed at the end of the chapter. 

J. Barrett, Atomic Structure and Periodicity, Royal Society of Chemistry, Cambridge, 2001. This book is meant to act as preliminary reading for the present text, but covers the subject matter in a largely non-mathematical way. The theoretical basis of the Periodic Table is dealt with in considerable detail and is followed by discussions of the periodicities of the main physical and chemical properties of the elements. 

ATOMIC NUMBER. The number of protons (positively charged mass units) in the nucleus of an atom, upon which its structure and properties depend. This number represents the location of an element in the periodic table. It is normally the same as the number of negatively charged electrons in the shells. Thus, an atom is electrically neutral except in an ionized state, when one or more electrons have been gained or lost. Atomic numbers range from 1, for hydrogen, to 110 for dannstadtium. 

PERIODIC LAW. Originally stated in recognition of an empirical periodic variation of physical and chemical properties of the elements with atomic weight, this law is now understood to he based fundamentally on atomic number and atomic structure. A modern statement is the electronic configurations of the atoms of the elements vary periodically with their atomic number. Consequently, all properties of the elements that depend on their atomic structure (electronic configuration) tend also to change with increasing atomic number in a periodic manner. 

Calculations using the methods of non-relativistic quantum mechanics have now advanced to the point at which they can provide quantitative predictions of the structure and properties of atoms, their ions, molecules, and solids containing atoms from the first two rows of the Periodical Table. However, there is much evidence that relativistic effects grow in importance with the increase of atomic number, and the competition between relativistic and correlation effects dominates over the properties of materials from the first transition row onwards. This makes it obligatory to use methods based on relativistic quantum mechanics if one wishes to obtain even qualitatively realistic descriptions of the properties of systems containing heavy elements. Many of these dominate in materials being considered as new high-temperature superconductors. 

Extensive studies of energy spectra and other characteristics of atoms and ions allow one to reveal general regularities in their structure and properties [255-257]. For example, by considering the lowest electronic configurations of neutral atoms, we can explain not only the structure of the Periodical Table of elements, but also the anomalies. The behaviour of the ionization energy of the outer electrons of an atom illustrates a shell structure of electronic configurations. 

Atomic spectroscopy continues to be one of the most important subjects of contemporary physics. Spectra are fundamental characteristics of atoms and ions, and are the main source of information on their structure and properties. Modem atomic spectroscopy studies the structure and properties of practically every atom of the Periodical Table as well as of ions of any ionization degree. The book contains a large number of new results, which have been mainly published in Russian and are therefore almost unknown to western scientists. 

Thus, making use of modern methods of theoretical atomic spectroscopy and available computer programs, one is in a position to fulfill more or less accurate purely theoretical (ab initio) or semi-empirical calculations of the energy spectra, transition probabilities and of the other spectroscopic characteristics, in principle, of any atom or ion of the Periodical Table, their isoelectronic sequences, revealing in this way their structure and properties, to model the processes in low- and high-temperature plasma. Such calculations could be done prior to the corresponding experimental measurements, instead of them, or after them to help to interpret the interesting phenomena found in experimental studies. 

Of course, what the students are really interested in is why thallium is poisonous. Surprisingly, thallium is toxic because it mimics potassium in the body. But why would thallium behave like potassium As we study the periodic table and chemical periodicity, there is no immediate reason to suspect that these two elements would have similar properties. A close look at the electron shell arrangement of thallium and potassium, however, reveals that both form +1 ions. Since Tl+ ions also happen to be similar in size to K+ ions, they are able to replace potassium ions in cellular processes. (Thallium poisoning is treated with a compound called Prussian blue, which binds to +1 ions and thus facilitates their removal from the body.) It is clear then that we cannot understand the toxicity of thallium without studying its atomic structure and electron distribution. But chemistry is only part of the story. The effects of thallium poisoning only make sense if the... 

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