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mass number
mass number often represented by the symbol A, the total number of nucleons (neutrons and protons) in the nucleus of an atom . All atoms of a chemical element have the same atomic number (number of protons in the nucleus) but may have different mass numbers (from having different numbers of... Read more |
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atomic mass
atomic mass the mass of a single atom , usually expressed in atomic mass units (amu). Most of the mass of an atom is concentrated in the protons and neutrons contained in the nucleus. Each proton or neutron weighs about 1 amu, and thus the atomic mass is always very close to the mass number ... Read more |
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ununquadium
ununquadium , artificially produced radioactive chemical element ; symbol Uuq; at. no. 114; mass number of most stable isotope 289; m.p., b.p., sp. gr., and valence unknown. Situated in Group 14 of the periodic table , it is expected to have properties similar to those of lead and tin . ... Read more |
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Atomic nuclei
Atomic Nucleus The atomic nucleus is a tiny massive entity at the center of an atom. Occupying a volume whose radius is 1/100,000 the size of the atom, the nucleus contains most (99.9%) of the mass of the atom. In describing the nucleus, we shall describe its composition,... Read more |
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atomic weight
atomic weight mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element , as contrasted with atomic mass , which is the mass of any individual isotope. Although the first atomic weights were calculated at the beginning of the 19th cent., it was not... Read more |
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Weapons of mass destruction
Weapons of Mass Destruction ¦ ALEXANDR IOFFE The concept of Weapons of Mass Destruction appeared during War World II after the use of atomic bombs. In the mass consciousness, weapons of mass destruction are usually associated first with atomic weapons, although the concept... Read more |
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ununhexium
ununhexium , artificially produced radioactive chemical element ; symbol Uuh; at. no. 116; mass number of most stable isotope 292; m.p., b.p., sp. gr., and valence unknown. Situated in Group 16 of the periodic table , it is expected to have properties similar to those of polonium and ... Read more |
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mass spectrograph
mass spectrograph device used to separate electrically charged particles according to their masses; a form of the instrument known as a mass spectrometer is often used to measure the masses of isotopes of elements. J. J. Thomson and F. W. Aston showed (c.1900) that magnetic and electric fields... Read more |
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nucleus
nucleus in physics, the extremely dense central core of an atom . The Nature of the Nucleus Composition Atomic nuclei are composed of two types of particles, protons and neutrons, which are collectively known as nucleons. A proton is simply the nucleus of an ordinary hydrogen atom, the lightest... Read more |
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hassium
hassium , artificially produced radioactive chemical element; symbol Hs; at. no. 108; mass number of most stable isotope 265; m.p., b.p., sp. gr., and valence unknown. Situated in Group 8 of the periodic table , it is expected to have properties similar to those of osmium . In 1984 a German... Read more |
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