Classification of the elements

Chemists today understand that the repetition of properties of elements occurs because the electron configurations of atoms exhibit repeating patterns. Thus, the arrangement of elements in the periodic table reflects the electron structures of atoms. 

For example, the group number of a representative element gives the number of valence electrons in an atom of that element. The group 3A element aluminum, for example, has the electron configuration ls 2s 2p 3s 3p or [Ne]3s 3p The three electrons in the third energy level (3s and 3p ) are the valence electrons of the aluminum atom. In a similar way, the period number of a representative element indicates the energy level of the valence electrons. Aluminum is in the third period, and aluminum s valence electrons are in the third energy level. 

How many valence electrons are in an atom of each of the following elements  

In which energy level are the valence electrons of the elements listed in question 8  

The transition metals are the d-block elements. In these elements, the highest-energy electrons are in the d sublevel of the energy level one less than the period number. Most d-block elements have two electrons in s orbitals, but in some, such as chromium and copper, the d sublevel borrows an electron from the s orbital to form half-filled (Cr) or filled (Cu) d orbitals. The remaining block is the f-block, or iimer transition metals. The highest-energy electrons in these elements are in an f sublevel of the energy level two less than the period number. 

Take a look at the electron configurahons for the group lA elements listed below. These elements comprise the first four periods of group lA. 

What do the four configurations have in common The answer is that they all have a single electron in their outermost energy level. 

To learn more about alternate periodic tables, visit the Chemistry Web site at chemistrymc.com 

Activity Research periodic tables that differ from the standard periodic table on pages 156-157. List three alternate versions of the standard periodic table and describe their differences. 

Would you like to analyze blood and tissue samples How about determining the chemical content of body fluids If so, you might enjoy being a medical lab technician. 

Real-World Reading Link A house number is not enough to deliver a letter to the correct address. More information, such as street name, city, and state, is necessary to deliver the letter. Similarly, chemical elements are identified according to details about the arrangement of their electrons. 

Valence electrons and period The energy level of an element s valence electrons indicates the period on the periodic table in which it is found. For example, lithium s valence electron is in the second energy levels and lithium is found in period 2. Now look at gallium, with its electron configuration of [Ar]4s 3d °4pb Gallium s valence electrons are in the fourth energy level, and gallium is found in the fourth period. 

Observe How does the number of valence electrons vary within a group  

Interactive Table Explore noble gas electron configurations at glencoe.com. 

Period Principal Energy Level Element Electron Configuration 

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R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

In this article it will be argued that the classification of the elements is an objective feature of the world and not open to conventional choice and relativism. It will also be argued that the element helium belongs objectively and most naturally either to the alkaline earths or the noble gases regardless of whether such a question may be settled at present.8... 

Bent claims that the periodic system should be primarily based on the structure of neutral atoms rather than on macroscopic properties of the elements. In doing so he claims support from none other than Mendeleev. Bent also claims to garner support from the writings of Mendeleev in steering clear of the properties of the elements as simple substances in crucial matters of classification of the elements. In fact, the identification of elements as basic substances with the atoms of the elements is... 

What will now be proposed is that in addition to its role in ordering the elements, the quantity Z may be used to also affect a secondary classification of the elements, that is, their placement into vertical groups in the sense of the conventional periodic table. In proposing this idea, I make use of what was historically the earliest hint of chemical periodicity, namely, the existence of triads of elements [35]. 

Very soon afterwards, however, two scientists independently produced the definitive statement on the classification of the elements - Julius Lothar Meyer (1830-95) in Germany and Dmitri Ivanovich Mendeleev (1834-1907) (also spelled Mendeleeff or Mendelejeff) in Russia. It is the latter who is now credited with the construction of the first periodic table. At the age of 35, Mendeleev was Professor of Chemistry at the University of St Petersberg, when he published his first paper (1869) on the periodic system. He was apparently unaware of the work of Newlands or Lothar Meyer, but came to the same conclusions, and was also prepared to go further, and predict that certain elements must remain to be discovered because of discrepancies in his table. Amongst other things, he concluded the following ... 

When Mendeleev first proposed his celebrated classification of the elements (1869), he found it necessary to leave a blank at the position now occupied by scandium. He did... 

Volume 3 explains the systems of molecular and atomic weight, valences, the atomic theory, the system of classification of the elements, and the laws of chemical equilibrium. Here we find Lespieau s view that the goal of chemistry is the formule developee, not the formule brute, and that the atomic hypothesis gives us a striking interpretation and creates a language that is now adopted by all chemists, even those who reject the hypothesis of an indivisible primordial particle.30... 

Geochemical subdivision of the Periodic Table. The Goldschmidt s geochemical classification of the elements in the Periodic Table is presented in Fig. 4.10... 

Anodier important advance in die classification of the elements was made by John Alexander Reina Newlands. He was born in Southwark, England, in 1837, and was educated privately by his father, a minister of... 

Another very early classification of the elements was made by Lewis Reeve Gibbes, professor of chemistry at the College of Charleston, South Carolina, who worked out the first version of his Synoptical Table of the Chemical Elements between 1870 and 1874, and in 1875 discussed an improved form of it before the Elliott Society of Charleston. The hardships of the reconstruction period, however, made prompt publication impossible. When the paper was finally published in 1886, it attracted little attention because the periodic tables of Lothar Meyer and Mendeleev were already well known (39). 

Taylor, W. H., Lewis Reeve Gibbes and the classification of the elements, ... 

The Electronic Configurations of Atoms the Periodic Classification of the Elements... 

The chemistry of an element is determined by the manner in which its electrons are arranged in the atom. Such arrangements are the basis of the modern periodic classification of the elements the Periodic Table. 

The treatment of atoms with more than one electron (polyelectronic atoms) requires consideration of the effects of interelectronic repulsion, orbital penetration towards the nucleus, nuclear shielding, and an extra quantum number (the spin quantum number) which specifies the intrinsic energy of the electron in any orbital. The restriction on numbers of atomic orbitals and the number of electrons that they can contain leads to a discussion of the Pauli exclusion principle, Hund s rules and the aufbau principle. All these considerations are necessary to allow the construction of the modern form of the periodic classification of the elements. 

In 1869, two scientists working independently and unaware of each other, Dmitri Mendeleev (a Russian chemist) and Lothar Meyer (a German scientist) made similar classifications of the elements. Both scientists classified the elements in the order of increasing atomic mass, and, as a result, they noticed some similar periodic properties among some elements. Mendeleev s work and ideas on periodic properties of elements attracted much attention. 

From a chemical point of view the most important result is that number theory predicts two alternative periodic classifications of the elements. One of these agrees with experimental observation and the other with a wave-mechanical model of the atom. The subtle differences must be ascribed to a constructionist error that neglects the role of the environment in the wave-mechanical analysis. It is inferred that the wave-mechanical model applies in empty space Z/N = 0.58), compared to the result, observed in curved non-empty space, (Z/N = t). The fundamental difference between the two situations reduces to a difference in space-time curvature. 

Extrapolation of the hem lines to Z/N = 1 defines another recognizable periodic classification of the elements, inverse to the observed arrangement at Z/N = t. The inversion is interpreted in the sense that the wave-mechanical ground-state electronic configuration of the atoms, with sublevels / < d < p < s, is the opposite of the familiar s < p < d < f. This type of inversion is known to be effected under conditions of extremely high pressure [52]. It is inferred that such pressures occur in regions of high space-time curvature, such as the interior of massive stellar objects, a plausible site for nuclear synthesis. 

These metals constitute the left-hand or A families in Groups I and II of the periodic classification of the elements, as shown in the table inside the back cover of the book. 

PERIODIC CLASSIFICATION OF THE ELEMENTS ACCORDING TO THEIR ATOMIC NUMBERS AND THE ARRANGEMENT OF THEIR ELECTRONS... 

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