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Periodic table |
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Periodic tableThe periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. The elements are arranged by electron structure so that many chemical properties vary regularly across the table. Each element is listed by its atomic number and chemical symbol. The standard table provides the necessary basics. There are also other methods for displaying the chemical elements for more details or different perspectives. GroupsA group is a vertical column in the periodic table of the elements. There are 18 groups in the standard periodic table. Elements in a group have similar configurations of their valence shell electrons, which gives them similar properties. Group numbersThere are three systems of group numbers; one using Arabic numerals, another using Roman numerals, and one using a combination of Roman numerals and Latin letters. The Roman numeral names are the original traditional names of the groups; the Arabic numeral names are a newer naming scheme recommended by the International Union of Pure and Applied Chemistry (IUPAC). The IUPAC scheme was developed to replace both older Roman numeral systems as they confusingly used the same names to mean different things. Standard periodic tableOther methods for displaying the chemical elements And here is the periodic table for magnetic resonance. Explanation of the structure of the periodic tableThe number of electron shells an atom has determines to which period it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s 5g 6f 7d 8p ... Hence the structure of the table. Since the outermost electrons determine chemical properties, those tend to be similar within groups. Elements adjacent to one another within a group have similar physical properties, despite their significant differences in mass. Elements adjacent to one another within a period have similar mass but different properties. For example, very near to nitrogen (N) in the second period of the chart are carbon (C) and oxygen (O). In contrast, very near to chlorine (Cl) in the next-to-last group in the chart (the halogens) are fluorine (F) and bromine (Br). HistoryMain article: History of the periodic table The original table was created without a knowledge of the inner structure of atoms: if one orders the elements by atomic mass, and then plots certain other properties against atomic mass, one sees an undulation or periodicity to these properties as a function of atomic mass.
This was followed by the English chemist John Alexander Reina Newlands, who in 1865 noticed that the elements of similar type recurred at intervals of eight, which he likened to the octaves of music, though his law of octaves was ridiculed by his contemporaries. Finally, in 1869, the German Lothar Meyer and the Russian chemist Dmitri Ivanovich Mendeleev almost simultaneously developed the first periodic table, arranging the elements by mass. However, Mendeleev plotted a few elements out of strict mass sequence in order to make a better match to the properties of their neighbours in the table, corrected mistakes in the values of several atomic masses, and predicted the existence and properties of a few new elements in the empty cells of his table. Mendeleev was later vindicated by the discovery of the electronic structure of the elements in the late 19th and early 20th century. Further resourcesSee also
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