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... ghts, exhibit an apparent periodicity of properties. 2. Elements, which are similar as regards their chemical properties, have atomic weights that are either of nearly the same value (eg. Pt, Ir, Os) or which increase regularly (e.g. K, Ru, Cs). 3.
The arrangement of the elements, or of groups of elements in the order of their atomic weights, corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, Ba, C, N, O, and Sn. 4. The elements which are the most widely diffused have small atomic weights. 5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body. 6. We must expect the discovery of many as yet unknown elements-for example, elements analogous to aluminium and silicon- whose atomic weight would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. 8. Certain characteristic properties of elements can be foretold from their atomic weights. (18) On November 29, 1870, Mendeleev took his concept even further by stating that it was possible to predict the properties of undiscovered elements.
He then proceeded to make predictions for three new elements (aluminium, boron and silicon) and suggested several properties of each, including density, radii, and combining ratios with oxygen, among others. The science world was perplexed, and many scoffed at Mendeleev's predictions. It was not until November 1875, when the Frenchman Lecoq de Boisbaudran discovered one of the predicted elements (aluminium), which he named Gallium that Dmitri's ideas were taken seriously. The other two elements were discovered later and their properties were found to be remarkably similar to those predicted by Mendeleev. These discoveries, verifying his predictions and proving his law, took him to the top of the science world. He was 35 years old when the initial paper was presented Throughout the remainder of his life, Dmitri Mendeleev received numerous awards from various organizations including the Davy Medal from the Royal Society of England in 1882, the Copley Medal, the Society's highest award, in 1905, and honorary degrees from universities around the world.
Following his resignation from the University of St. Petersburg, the Russian government in 1893 appointed him Director of the Bureau of Weights and Measures. This was believed to have been done to keep down public disapproval of the government. Mendeleev continued to be a popular social figure until his death, on January 20, 1907 at the age of 73The set out of the Periodic TableThere were some inconsistencies in the arrangement of the elements according to his law, however it wasn't until the early 1900's (1914) that a Prof Moseley, a British Physicist, was able to determine the atomic numbers of all the known elements using an experimental technique. Moseley then proceeded to rearrange the elements according to increasing atomic numbers. Moseley's arrangement seemed to clear up the contradictions and inconsistencies of Mendeleev's arrangement, but Moseley based his arrangement on atomic numbers and not atomic masses. Moseley's periodic law is now considered the current Periodic Law.
It resulted in a slight alteration of Mendeleev's arrangement, but the slight difference was enough to correct the inconsistencies that existed in Mendeleev's arrangement. The elements are arranged in vertical columns known as Groups. The elements in each group have consistently high or low values for certain properties. The horizontal rows of elements are referred to as 'periods' Group 1 is called the alkali metal group. These are strong metals that are unusually soft and very reactive toward Oxygen forming Oxides and water forming hydroxides of the metal. These elements are so reactive toward Oxygen and water vapour that they are stored under an inert liquid to protect them from Oxygen and water vapour.
Group 2 is called the alkaline earth metals. These metals are not as soft as Group 1 metals. They also react more mildly with Oxygen to produce oxides of the metals and only react with water at temperatures where the water is steam. Groups 3-12 are referred to as the transition metal groups. These metals are not as predictable because of the shielding effect of the inner electrons. Groups 1-2 and 13-18 are referred to as the representative elements Group 17 is referred to as the halogen group Group 18 is referred to as the Noble gas group previously known as the inert gas group.
There are two special series of elements that occur right after the transition metal element Actinium (Actinides) and Lanthanum (Lanthanides). The Modern Periodic TableThe ideas of Mendeleev have led to huge developments in the Periodic Table. His principles on producing the table have made it easy to produce new versions of the table when new elements are discovered. Here is a copy of the current periodic table Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18Period 1 1H 2He2 3Li 4Be 5B 6C 7N 8O 9F 10Ne3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe6 55Cs 56Ba * 71Lu 72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po 85At 86Rn7 87Fr 88Ra ** 103Lr 104Rf 105Db 106Sg 107Bh 108Hs 109Mt 110Uun 111Uuu 112Uub 113Uut 114Uuq 115Uup 116Uuh 117Uus 118Uuo *Lanthanoids * 57La 58Ce 59Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb **Actinoids ** 89Ac 90Th 91Pa 92U 93Np 94Pu 95Am 96Cm 97Bk 98Cf 99Es 100Fm 101Md 102No .Discovery of ElementsThe table below (that was provided to me by chemicalelements.com) shows the date of which the elements were discovered. Many elements have been known since the Ancient Civilisations (i.e. Sulphur, copper, Lead and Silver). Others such as Ununbium have been discovered in recent years (1996).
Some elements also have no known date of discovery. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 181 H He 1766 18952 Li Be B C N O F Ne 1817 1798 1808 * 1772 1774 1886 18983 Na Mg Al Si P S Cl Ar 1807 1808 1825 1823 1669 * 1774 18944 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 1807 1808 1879 1791 1830 1797 1774 * 1737 1751 * 1746 1875 1886 * 1817 1826 18985 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 1861 1790 1794 1789 1801 1778 1937 1844 1803 1803 * 1817 1863 * * 1782 1804 18986 Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 1860 1808 1923 1802 1783 1925 1804 1804 1735 * * 1861 * * 1898 1940 18987 Fr Ra ** Rf Db Sg Bh Hs Mt Uun Uuu Uub 1939 1898 1969 1970 1974 1976 Disputed 1982 1987 1994 1996 * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1839 1803 1885 1925 1945 1879 1901 1880 1843 1886 1878 1843 1879 1878 1907 ** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 1899 1828 1917 1789 1940 1940 1945 1944 1949 1950 1952 1953 1955 1957 1961* Known to ancient civilizationsElement Groups (Families)Alkali Earth Alkaline Earth Transition MetalsRare Earth Other Metals MetalloidsNon-Metals Halogens Noble Gases.
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