Debye
Encyclopedia
The debye is a CGS unit (a non-SI
metric
unit) of electric dipole moment
Electric dipole moment is defined as charge times displacement:
-centimeter.The statcoulomb is also known as the franklin or electrostatic unit of charge.
Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10-10 statcoulomb10-10 statcoulomb is approximately 0.2083 units of elementary charge. (generally called e.s.u. (electrostatic unit) in older literature), which were separated by 1 ångström
.The ångström is of an order of magnitude close to that of a typical covalent bond
.
This gave a convenient unit for molecular dipole moments.
Typical dipole moments for simple diatomic molecules are in the range of 0 to 11 D. Symmetric homoatomic species, e.g. chlorine
, Cl2, have zero dipole moment and highly ionic molecular species have a very large dipole moment, e.g. gas phase potassium bromide
, KBr, with a dipole moment of 10.5 D.
The debye is still used in atomic physics
and chemistry
because SI units are inconveniently large. The smallest SI unit of electric dipole moment is the yoctocoulomb-meter, which is roughly 300,000 D.Yocto-, with a value of 10−24, is the smallest SI prefix
. Note that SI disallows the application of prefixes to both members of a compound unit or the compounding of prefixes, thus ruling out such units as the femtocoulomb-femtometer or the microyoctocoulomb-meter (both approximately 0.3 D) respectively. There is currently no satisfactory solution to this problem of notation without resorting to the use of scientific notation.
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
metric
Metric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...
unit) of electric dipole moment
Electric dipole moment
In physics, the electric dipole moment is a measure of the separation of positive and negative electrical charges in a system of charges, that is, a measure of the charge system's overall polarity with SI units of Coulomb-meter...
Electric dipole moment is defined as charge times displacement:
- p = qr
Statcoulomb
The statcoulomb or franklin or electrostatic unit of charge is the physical unit for electrical charge used in the centimetre-gram-second system of units and Gaussian units. It is a derived unit given by...
-centimeter.The statcoulomb is also known as the franklin or electrostatic unit of charge.
| 1 statC | =1 Fr |
| =1 esu |
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
.The ångström is of an order of magnitude close to that of a typical covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
.
| 1 Å | = 100 pm |
| = 10-8 cm | |
| = 10-10 m |
| 1 D | = 10-18 statC·cm |
| = 10-10 esu·Å | |
| = C·m Metre The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology... One debye equals 1 C·m2/s divided by the speed of light in vacuum. Conversely 1 C·m = 2.9979 D. |
|
| ≈ 3.33564 C·m | |
| ≈ 1.10048498 qPlP Planck units In physics, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants listed below, in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Planck units elegantly simplify... |
|
| ≈ 0.393430307 ea0 Atomic units Atomic units form a system of natural units which is especially convenient for atomic physics calculations. There are two different kinds of atomic units, which one might name Hartree atomic units and Rydberg atomic units, which differ in the choice of the unit of mass and charge. This article... |
|
| ≈ 0.20822678 eÅ |
Typical dipole moments for simple diatomic molecules are in the range of 0 to 11 D. Symmetric homoatomic species, e.g. chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, Cl2, have zero dipole moment and highly ionic molecular species have a very large dipole moment, e.g. gas phase potassium bromide
Potassium bromide
Potassium bromide is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the United States. Its action is due to the bromide ion...
, KBr, with a dipole moment of 10.5 D.
The debye is still used in atomic physics
Atomic physics
Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and...
and chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
because SI units are inconveniently large. The smallest SI unit of electric dipole moment is the yoctocoulomb-meter, which is roughly 300,000 D.Yocto-, with a value of 10−24, is the smallest SI prefix
SI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
. Note that SI disallows the application of prefixes to both members of a compound unit or the compounding of prefixes, thus ruling out such units as the femtocoulomb-femtometer or the microyoctocoulomb-meter (both approximately 0.3 D) respectively. There is currently no satisfactory solution to this problem of notation without resorting to the use of scientific notation.