Natural abundance refers to the prevalence of different isotopes of an element as found in nature. The weighted (by natural abundance) averagemass of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an element varies from planet to planet. Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because the contain different numbers of neutrons. ... A chemical element, often called simply element, is the class of atoms which contain the same number of protons. ... The deepest visible-light image of the universe, the Hubble Ultra Deep Field. ... In statistics, given a set of data, X = { x1, x2, ..., xn} and corresponding weights, W = { w1, w2, ..., wn} the weighted mean is calculated as Note that if all the weights are equal, the weighted mean is the same as the arithmetic mean. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... ... The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. ...
Percent natural abundances refer to the relative proportions, expressed as percentages by number, in which the isotopes of an element are found in natural sources.
'Natural' is defined as "of or relating to nature"; this applies to both definitions of 'nature': 'essence' ("one's true nature") and 'the untouched world' ("force of nature").
The natural sciences such as physics, chemistry etc. Natural history is a category for the study of the history of living things.
Naturalism (philosophy): the philosophical stance based on materialism and pragmatism, that rejects the validity of explanations or theories making use of entities inaccessible to natural science (see supernatural).
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