Atomvægte

Atomvægte, also known as atomic weights, represent the average mass of atoms of an element, taking into account the relative abundance of its isotopes. These values are typically expressed in atomic mass units (amu), where one amu is defined as one-twelfth the mass of an atom of carbon-12. It is important to distinguish atomic weight from the mass number, which is the total count of protons and neutrons in an atom's nucleus and is always an integer.

The atomic weight of an element is determined by averaging the masses of its naturally occurring isotopes, each weighted by its fractional abundance. For instance, chlorine exists as chlorine-35 and chlorine-37, and its atomic weight is a weighted average of these two isotopes. This averaging process explains why most atomic weights are not whole numbers.

Atomic weights are fundamental constants used extensively in chemistry and physics. They are crucial for calculating molar masses, which are used in stoichiometry to determine the amount of reactants and products in chemical reactions. These values are periodically compiled and updated by organizations like the International Union of Pure and Applied Chemistry (IUPAC). Understanding atomic weights is essential for quantitative chemical analysis and for comprehending the composition and behavior of matter.