Atomic mass units (amu) are used for elements on the periodic table instead of actual masses for several reasons:
Standardization: Atomic mass units provide a standardized scale for comparing the masses of different elements. Since atoms are extremely small and their masses can vary significantly, it is impractical to use actual masses, which would involve large numbers. Atomic mass units provide a more convenient and manageable scale for expressing these masses.
Relative Mass: Atomic mass units represent relative masses of atoms. The atomic mass of an element is a weighted average of the masses of its naturally occurring isotopes, taking into account their relative abundances. By using atomic mass units, elements can be compared in terms of their relative masses rather than absolute masses.
Isotopic Variation: Many elements exist as a mixture of isotopes, which are atoms of the same element with different numbers of neutrons. These isotopes have different masses, and their relative abundances can vary in different samples. Using atomic mass units allows for a representation of the average mass of an element, considering the isotopic variation.
Precision and Accuracy: The use of atomic mass units allows for more precise and accurate measurements. Atomic masses are determined experimentally using various techniques, including mass spectrometry. The atomic mass unit scale is based on the mass of a specific isotope of carbon, carbon-12, which is assigned a mass of exactly 12 amu. This provides a reference point for the atomic masses of other elements.
Simplification: Expressing atomic masses in atomic mass units simplifies calculations in chemistry and other scientific disciplines. Atomic mass units are used in various formulas and equations to determine the stoichiometry of chemical reactions, calculate molar masses, and perform other calculations involving atomic masses. The use of atomic mass units avoids the need for complex conversions involving large numbers.
In summary, atomic mass units are used on the periodic table to provide a standardized scale for comparing the relative masses of elements, considering their isotopic variations. They simplify calculations and provide a convenient and manageable representation of atomic masses.