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Kids.Net.Au - Encyclopedia > Atomic weight (267 words) |
 | The atomic weight (or, more accurately, the atomic mass) of an isotope of a chemical element is the mass of one atom of that isotope, expressed in units (atomic mass unit, amu) such that the Carbon-12 isotope receives atomic weight 12. |
| The atomic weight of a chemical element is defined as the average atomic weight of its isotopes. |
| For example, the atomic weight of iron is 55.847, and therefore one mole of iron atoms weighs 55.847 grams. |
| atomic weight - Encyclopedia.com (1671 words) |
| 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 until the discovery of isotopes by F. Soddy (c.1913) that the atomic mass of many individual isotopes was determined, leading eventually to the adoption of the atomic mass unit as the standard unit of atomic weight. |
| The atomic mass and relative abundance of the isotopes of an element can be measured very accurately and with relative ease by this method, whereas chemical determination of the atomic weight of an element requires a careful and precise quantitative analysis of as many of its compounds as possible. |
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