The second half of the century. Century was marked by the discovery of several new elements, which

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Periodic table of elements is required in any chemistry laboratory in the world. Today. it contains 112 elements arranged according to their properties. People have thought about the possibility of arranging items in a certain order, just before the Rutherford and Bohr to develop models of the atom. In 1829, German chemist Johann Dobereiner observed several groups of three elements that had similar chemical properties. He called these groups valvoline triads. One of the triad was composed of colored gases miss, bromine and iodine. Metals such as lithium, sodium and potassium, which reacts strongly valvoline with the other elements form a triad other. Dobereiner noticed valvoline that the atomic mass of an element in the middle of the triad has about the same value as the other two elements of mass media.
The second half of the century. Century was marked by the discovery of several new elements, which represented an important step in their classification and putting valvoline them in a systematic order. In 1869, Russian chemist valvoline Dimitri Mendeleev and German chemist Lothar Meyer independently developed the periodic table. Dmitri valvoline Mendeleev stated valvoline that atomic weight determines the character of an element. Therefore, he arranged the elements in increasing order of their atomic weight and grouped elements with similar properties in vertical columns. In the table you created, Mendeleev left spaces in the aluminum and silicon for further discoveries. The discovery, more than 100 years, gallium and germanium which had anticipated chemical properties contributed greatly to the acceptance of Mendeleev periodic table in the scientific world.
The periodic table contains the symbols of chemical valvoline elements arranged according to the atomic valvoline number of each item. This corresponds to the number of positively charged particles (protons) which are located in the nucleus of the atom, but the atoms are electrically neutral atomic number is equal to the number of electrons in an atom is found or orbit " coatings "surrounding the core. Hydrogen atoms (symbol: H) has the simplest structure, the core containing a single valvoline proton. Weight valvoline or atomic mass increases with atomic number. By the uranium atom contains 92 protons and is the one higher. The number of electrons in the outermost shell situated atomic determined in large measure chemical properties of the elements. Elements with similar properties are arranged in vertical groups. For example, all the Eighteenth Group ("noble gases") contain eight electrons in the outer shell, except helium, and does not react with other elements. Horizontal rows in the table is "period" (from 1-7) and the vertical columns are "groups" (from 1-18).
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