atomic number

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The Columbia Encyclopedia, Sixth Edition

atomic number

The Columbia Encyclopedia, Sixth Edition | 2008 | The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press. (Hide copyright information) Copyright

atomic number often represented by the symbol Z, the number of protons in the nucleus of an atom , as well as the number of electrons in the neutral atom. Atoms with the same atomic number make up a chemical element . Atomic numbers were first assigned to the elements c.1913 by H. G. J. Moseley; he arranged the elements in an order based on certain characteristics of their X-ray spectra and then numbered them accordingly. The elements are now arranged in the periodic table in the order of their atomic numbers. Mendeleev's periodic law was originally based on atomic weights . See mass number .

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atomic number

World Encyclopedia | 2005 | © World Encyclopedia 2005, originally published by Oxford University Press 2005. (Hide copyright information) Copyright

atomic number (proton number) Number of protons in the nucleus of an atom of an element, which is equal to the number of electrons moving around that nucleus. It is abbreviated to ‘at.no.’ and represented by the symbol Z. The atomic number determines the chemical properties of an element and its position in the periodic table. Isotopes of an element all have the same atomic number but a different atomic mass number.
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