<P> For example, carbon - 12, carbon - 13 and carbon - 14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively . The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively . </P> <P> A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon - 13 with 6 protons and 7 neutrons . The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, whereas the isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear . The neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements . Even in the case of the lightest elements where the ratio of neutron number to atomic number varies the most between isotopes it usually has only a small effect, although it does matter in some circumstances (for hydrogen, the lightest element, the isotope effect is large enough to strongly affect biology). The term isotopes (originally also isotopic elements, now sometimes isotopic nuclides) is intended to imply comparison (like synonyms or isomers), for example: the nuclides,, are isotopes (nuclides with the same atomic number but different mass numbers), but Ar,, Ca are isobars (nuclides with the same mass number). However, because isotope is the older term, it is better known than nuclide, and is still sometimes used in contexts where nuclide might be more appropriate, such as nuclear technology and nuclear medicine . </P> <P> Isotopes are atoms of the same element having the same numbers of protons (atomic number), but different numbers of neutrons . They have same chemical properties due to the same electron configuration, but different physical properties . </P> <P> An isotope and / or nuclide is specified by the name of the particular element (this indicates the atomic number) followed by a hyphen and the mass number (e.g. helium - 3, helium - 4, carbon - 12, carbon - 14, uranium - 235 and uranium - 239). When a chemical symbol is used, e.g. "C" for carbon, standard notation (now known as "AZE notation" because A is the mass number, Z the atomic number, and E for element) is to indicate the mass number (number of nucleons) with a superscript at the upper left of the chemical symbol and to indicate the atomic number with a subscript at the lower left (e.g. He, He,,, U, and U). Because the atomic number is given by the element symbol, it is common to state only the mass number in the superscript and leave out the atomic number subscript (e.g. He, He,,, U, and U). The letter m is sometimes appended after the mass number to indicate a nuclear isomer, a metastable or energetically - excited nuclear state (as opposed to the lowest - energy ground state), for example Ta (tantalum - 180m). </P>

How to identify the isotope of an element
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