relative atomic mass

Thân thiện

A student calculates the relative atomic mass of carbon from a periodic table.

Definition

Noun 1. (Chemistry) The average mass of an atom of a chemical element, expressed in atomic mass units (amu or u). It is a dimensionless physical quantity calculated as the weighted average of the masses of all naturally occurring isotopes of an element, relative to one-twelfth the mass of an atom of carbon-12.

Usage

• This term is used in scientific contexts, primarily in chemistry and physics, to specify the mass of atoms for calculations and comparisons.
• It is often used interchangeably with "atomic weight" in many contexts, though "relative atomic mass" is the more precise modern term.
• It is typically followed by the element it describes.

Examples

• The relative atomic mass of hydrogen is approximately 1.008.
• To calculate the mass of a compound, you must sum the relative atomic masses of its constituent elements.
• The periodic table lists the relative atomic mass for each element.

Advanced Usage

• "Relative isotopic mass" is a related term referring to the mass of a specific isotope of an element, relative to the carbon-12 standard.
• The value is a weighted average, meaning it accounts for the abundance of each isotope in a naturally occurring sample. For example, chlorine's relative atomic mass of 35.45 reflects the mix of chlorine-35 and chlorine-37 isotopes.

Variants and Related Words

• Atomic Weight (n): A largely synonymous term, though historically it was defined differently. In modern use, it is often considered equivalent to relative atomic mass.
• Standard Atomic Weight (n): A more specific value published by IUPAC, representing the best knowledge of atomic weight variations in normal materials.

Synonyms

• Atomic weight (in modern, non-technical contexts)

Notes

• The value is dimensionless because it is a ratio (mass of an atom / (1/12 mass of carbon-12 atom)).
• It is a crucial value for stoichiometric calculations in chemistry, such as determining molar masses and balancing chemical equations.

Học thuật

Noun

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

Từ đồng nghĩa

• atomic mass
• atomic weight