Atomic weight

Atomic weight is a term used in chemistry and physics to represent the average mass of atoms of an element. It is usually expressed in atomic mass units (amu), where 1 amu is approximately equal to the mass of a single proton or neutron.

Definition

The atomic weight of an element is calculated as the weighted average of the atomic masses of the naturally occurring isotopes of that element. The atomic masses of isotopes are determined by the number of protons and neutrons in the nucleus of the atom. The atomic weight of an element can vary depending on the source of the material, due to the presence of different isotopes.

Measurement

The atomic weight of an element is measured using mass spectrometry. This technique involves ionizing atoms and then separating them based on their mass-to-charge ratio. The resulting spectrum can be used to determine the relative abundances of different isotopes, which can then be used to calculate the atomic weight.

Applications

Atomic weight is a fundamental property of elements and is used in many areas of science and engineering. It is used in stoichiometry to calculate the amounts of reactants and products in chemical reactions. It is also used in isotope geochemistry to understand the processes that have shaped the Earth over geological timescales.

See also

• Atomic number
• Isotope
• Periodic table
• Stoichiometry