atomic weight

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atomic weight

The atomic weight of carbon is approximately 12.01.

Definition
  1. Noun:
    • (Chemistry) The mass of an atom of a chemical element expressed in atomic mass units: It is a weighted average of the masses of all the naturally occurring isotopes of an element, relative to the mass of an atom of carbon-12, which is defined as exactly 12 atomic mass units.
Usage
  • As a subject or object in a sentence: The term "atomic weight" is used to discuss the relative mass of an element's atoms in chemical calculations and discussions.
  • Key Point: Although the term uses "weight," it is a measure of relative atomic mass and is dimensionless, but is expressed in atomic mass units (u or Da).
Examples
  • Noun:
    • The atomic weight of hydrogen is approximately 1.008.
    • In the periodic table, elements are arranged in order of increasing atomic number, not atomic weight.
    • Scientists use the atomic weight to calculate molecular weights for compounds.
Advanced Usage
  • "Standard atomic weight": Refers to the recommended value published by IUPAC (International Union of Pure and Applied Chemistry), which is often given as an interval to reflect natural isotopic variation.
    • The standard atomic weight of boron is listed as [10.806, 10.821].
  • Distinction from "atomic mass": In modern terminology, "atomic weight" is often used synonymously with "relative atomic mass," while "atomic mass" can refer to the mass of a specific isotope.
    • The atomic mass of carbon-12 is exactly 12 u, while its atomic weight is 12.011.
Variants and Related Words
  • Relative atomic mass (Aᵣ): The modern, more precise term for atomic weight.
  • Atomic mass unit (amu or u): The standard unit of mass used for expressing atomic and molecular masses. One atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom.
  • Isotopic mass: The mass of a specific isotope of an element.
Synonyms
  • Relative atomic mass: The preferred term in modern scientific contexts.
  • Mean atomic mass: Emphasizes it is an average.
Related Phrases
  • To determine the atomic weight: A phrase describing the process of calculating or measuring this value.
    • Early chemists worked to determine the atomic weight of elements.
  • Based on atomic weight: A phrase indicating a calculation or order uses this value.
    • Mendeleev's first periodic table was based on atomic weight.
atomic weight

The atomic weight of carbon is approximately 12.01.

Noun
  1. (chemistry) the mass of an atom of a chemical element expressed in atomic mass units

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