Potassium argon dating definition
Isotope, one of two or more species of atoms of a chemical element with the same atomic number and position in the periodic table and nearly identical chemical behaviour but with different atomic masses and physical properties. An atom is first identified and labeled according to the number of protons in its nucleus. The great importance of the atomic number derives from the observation that all atoms with the same atomic number have nearly, if not precisely, identical chemical properties. In particular, ores of the radioactive elements uranium and thorium had been found to contain small quantities of several radioactive substances never before observed.
A large collection of atoms with the same atomic number constitutes a sample of an element. These substances were thought to be elements and accordingly received special names.
Modeled on an analogy to a liquid drop, the first term represents the favourable contribution to the binding of the nucleus made by short-range, attractive nuclear forces between neutrons and protons.
This correction is necessitated by the observation that the nuclear charge distribution becomes somewhat more spread out near the surface of the nucleus.A uniform scale of nuclear stability, one that applies to stable and unstable isotopes alike, is based on a comparison of measured isotope masses with the masses of their constituent electrons, protons, and neutrons.For this purpose, electrons and protons are paired together as hydrogen atoms.A few years later, Soddy published a comparison of the atomic masses of the stable element lead as measured in ores rich in uranium and thorium, respectively.He expected a difference because uranium and thorium decay into different isotopes of lead.
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A bar of pure uranium, for instance, would consist entirely of atoms with atomic number 92. Uranium ores, for example, yielded ionium, and thorium ores gave mesothorium.