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The atomic mass (ma or m) is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1 Da is defined as 1⁄12 of the mass of a free carbon-12 atom at rest in its ground state. [1]
Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration (change of velocity) when a net force is applied. [1] The object's mass also determines the strength of its gravitational attraction to other bodies. The SI base unit of mass is the kilogram (kg).
Atomic units. The atomic units are a system of natural units of measurement that is especially convenient for calculations in atomic physics and related scientific fields, such as computational chemistry and atomic spectroscopy. They were originally suggested and named by the physicist Douglas Hartree. [1]
Mass number. A = (Relative) atomic mass = Mass number = Sum of protons and neutrons. N = Number of neutrons. Z = Atomic number = Number of protons = Number of electrons. A = Z + N {\displaystyle A=Z+N\,\!} Mass in nuclei. M'nuc = Mass of nucleus, bound nucleons. MΣ = Sum of masses for isolated nucleons.
In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB (described further below). Expressing one of these physical constants in terms of Planck units yields a numerical value of 1. They are a system of natural units ...
This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10 −27 kg. [61] Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 Da. [ 62 ] The value of this number is called the atomic mass .
"The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10 −34 when expressed in the unit J s, which is equal to kg m 2 s −1, where the metre and the second are defined in terms of c and ∆ν Cs." [1] The mass of one litre of water at the temperature ...
In 1803 John Dalton proposed to use the (still unknown) atomic mass of the lightest atom, hydrogen, as the natural unit of atomic mass. This was the basis of the atomic weight scale. [12] For technical reasons, in 1898, chemist Wilhelm Ostwald and others proposed to redefine the unit of atomic mass as 1 / 16 the mass of an oxygen atom. [13]