The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons. Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. The conventional symbol Z comes from the German word Zahl meaning number.
About Atomic number in brief
The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons. Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes, and the average isotopic mass of an isotopic mixture for an element in a defined environment on Earth, determines the element’s standard atomic weight. The conventional symbol Z comes from the German word Zahl meaning number, which, before the modern synthesis of ideas from chemistry and physics, merely denoted an element’s numerical place in the periodic table, whose order is approximately, but not completely, consistent with the order of the elements by atomic weights. In 1911, Ernest Rutherford gave a model of the atom in which a central nucleus held most of the atoms’ mass and a positive charge which, in units of the electron’s charge, was to be approximately equal to half the atom’s atomic weight, expressed in numbers of hydrogen atoms.
This central charge would thus be approximately half the atomic weight, the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford’s estimation that gold had a central charge of about 100, a month after Rutherford’s paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electron in an atom was exactly equal to its place in a periodic table. In 1913, Henry Moseley measured the wavelengths of the innermost photon transitions produced by the elements from aluminum to gold used as a series of movable anodic targets inside an x-ray tube. The square root of the frequency of these photons increased from one to the next. This led to the conclusion that the element Z must have 15 other things, i.e. members of the lanthanide series. From 1918 to 1947, seven of these elements were discovered.
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This page is based on the article Atomic number published in Wikipedia (as of Jan. 04, 2021) and was automatically summarized using artificial intelligence.
