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Hartree defined units based on three physical constants: [1]: 91 Both in order to eliminate various universal constants from the equations and also to avoid high powers of 10 in numerical work, it is convenient to express quantities in terms of units, which may be called 'atomic units', defined as follows:
Unit Remarks Name Symbol Definition Name Symbol relative atomic mass: A r: Ratio of the average mass per atom of an element to 1/12 of the mass of an atom of the nuclide 12 C one 1 Formerly called atomic/molecular weight. Example: A r (Cl) = 35.453. Both quantities depend on the nuclidic composition. relative molecular mass: M r
Quantities, Units and Symbols in Physical Chemistry, also known as the Green Book, is a compilation of terms and symbols widely used in the field of physical chemistry. It also includes a table of physical constants , tables listing the properties of elementary particles , chemical elements , and nuclides , and information about conversion ...
Symbol Name Meaning SI unit of measure alpha: alpha particle: angular acceleration: radian per second squared (rad/s 2) fine-structure constant: unitless beta: velocity in terms of the speed of light c: unitless beta particle: gamma: Lorentz factor: unitless photon: gamma ray: shear strain: radian
The atomic units have been chosen to use several constants relating to the electron: the electron mass, the elementary charge, the Coulomb constant and the reduced Planck constant. The unit of energy in this system is the total energy of the electron in the Bohr atom and called the Hartree energy. The unit of length is the Bohr radius.
Atomic weight: M: chemistry (mass of one atom divided by the atomic mass constant, 1 Da) Bodenstein number: Bo or Bd = / = Max Bodenstein: chemistry (residence-time distribution; similar to the axial mass transfer Peclet number) [2] Damköhler numbers: Da
While the values of the physical constants are independent of the system of units in use, each uncertainty as stated reflects our lack of knowledge of the corresponding value as expressed in SI units, and is strongly dependent on how those units are defined. For example, the atomic mass constant is exactly known when expressed using the dalton ...
Some quantities are known as several different names such as the magnetic B-field which is known as the magnetic flux density, the magnetic induction or simply as the magnetic field depending on the context. Similarly, surface tension can be denoted by either σ, γ or T. The table usually lists only one name and symbol that is most commonly used.