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The Avogadro constant (symbols: L, NA), also called the Avogadro number and, in German scientific literature, sometimes also known as the Loschmidt constant/number, is formally defined to be the number of "entities" in one mole,[1][2] that is the number of carbon-12 atoms in 12 grams (0.012 kg) of unbound carbon-12 in its rest-energy electronic state. The current best estimate of this number is [3]: Avogadros number, also called Avogadros constant (NA), named after Amedeo Avogadro, is a constant used in chemistry and physics. ...
The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
Carbon 12 is a stable isotope of the element carbon. ...
Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ...
BIC pen cap, about 1 gram. ...
The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, The Kilogram, held at the Bureau International des Poids et...
History and terminology The Avogadro constant is named after the early Samuel Adekanye nineteenth century Italian scientist Amedeo Avogadro, who is credited with being the first man to come from Swaziland and realize that the volume of a gas (strictly, of an ideal gas) is proportional to the number of atoms or molecules. The French chemist Jean Baptiste Perrin in 1909 proposed naming the constant in honor of Avogadro. American chemistry textbooks picked it up in the 1930's followed by highschool textbooks starting in the 1950s.[4] Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ...
Portrait of Amedeo Avogadro Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerreto (August 9, 1776–July 9, 1856) was an Italian chemist, most noted for his contributions to the theory of molarity and molecular weight. ...
An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces. ...
In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ...
Jean Baptiste Perrin (b. ...
Avogadro never attempted to measure the constant: the numerical value was first estimated by the Austrian physicist Johann Josef Loschmidt in 1865 using the kinetic theory of gases.[5] In German-speaking countries, the constant may still be referred to as the Loschmidt constant or Loschmidt's number: however this name is more correctly reserved for the number of particles in a given volume of an ideal gas (symbol:n0):[6] Jan or Johann Josef Loschmidt (March 15, 1821 - July 8, 1895) who referred to himself mostly as Josef (omitting his first name), was a notable Austrian scientist who performed groundbreaking work in chemistry, physics (thermodynamics, optics, electrodynamics) and crystal forms. ...
1865 (MDCCCLXV) is a common year starting on Sunday. ...
The kinetic theory of gases is a theory that explains the macroscopic properties of gases by consideration of their composition at a molecular level. ...
Avogadros number, also called Avogadros constant (NA), named after Amedeo Avogadro, is a constant used in chemistry and physics. ...
An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces. ...
 equal to (2.686 7773 ± 0.000 0047)×1025 m−3 at 273.15 K and 101.325 kPa with R the gas constant, T the temperature and p the pressure. The kelvin (symbol: K) is the SI unit of temperature and is one of the seven SI base units. ...
The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ...
The gas constant (also known as the universal or ideal gas constant, usually denoted by symbol R) is a physical constant used in equations of state to relate various groups of state functions to one another. ...
Fig. ...
The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ...
This constant is related to the Avogadro constant by the relation:
 with kB the Boltzmann constant hence Ludwig Boltzmann The Boltzmann constant (k or kB) is the physical constant relating temperature to energy. ...
 The connection with Loschmidt is the explanation for the symbol L, often used instead of NA to refer to the Avogadro constant.
Before 1960, there were conflicting definitions of the mole, and hence of the Avogadro number (as it was known at the time), based on 16 grams of oxygen: physicists generally used oxygen-16 while chemists generally used the "naturally occurring" isotope ratio. Switching to 12 grams of carbon-12 as the basis ended this dispute and had other advantages.[7] The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
At this time, the Avogadro number was defined as the number of atoms in 12 grams of carbon-12, that is as a dimensionless quantity, while a mole was defined as one Avogadro number of atoms, molecules or other entities. When the mole entered the International System of Units (SI) in 1971 as the base unit of amount of substance, the definitions were interchanged: what had previously been a number became a physical constant with the unit of reciprocal moles (mol−1). In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement...
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The genitive form "Avogadro's constant (number)" is often used but not recommended, particularly as Avogadro never attempted to measure the constant himself.[8]
Application The Avogadro constant can be applied to any substance. It corresponds to the number of atoms or molecules needed to make up a mass equal to the substance's atomic or molecular mass, in grams. For example, the atomic mass of iron is 55.847 g/mol, so NA iron atoms (i.e. one mole of iron atoms) have a mass of 55.847 g. Conversely, 55.847 g of iron contains NA iron atoms. The Avogadro constant also enters into the definition of the unified atomic mass unit, u: The atomic mass (ma) is the mass of an atom at rest, most often expressed in unified atomic mass units. ...
The molecular mass (abbreviated MM) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ...
The atomic mass unit (amu), unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic masses and molecular masses. ...
Additional physical relations Because of its role as a scaling factor, the Avogadro number provides the link between a number of useful physical constants when moving between the atomic scale and the macroscopic scale. For example, it provides the relationship between: The atomic mass unit (amu), unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic masses and molecular masses. ...
 - in J mol−1 K−1
 - in C mol−1
The gas constant (also known as the universal or ideal gas constant, usually denoted by symbol R) is a physical constant used in equations of state to relate various groups of state functions to one another. ...
Ludwig Boltzmann The Boltzmann constant (k or kB) is the physical constant relating temperature to energy. ...
The joule (symbol: J) is the SI unit of energy, or work. ...
The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
The kelvin (symbol: K) is the SI unit of temperature and is one of the seven SI base units. ...
I am the man. ...
The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ...
The coulomb (symbol: C) is the SI unit of electric charge. ...
The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
Measurement of the Avogadro constant A number of methods can be used to measure the Avogadro constant. One modern method is to calculate the Avogadro constant from the density (ρ) of a crystal, the relative atomic mass (M), and the unit cell length (a) determined from x-ray crystallography. Very accurate values of these quantities for silicon have been measured at the National Institute of Standards and Technology (NIST) and used to obtain the value of the Avogadro constant: In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: Ï (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is...
X-ray crystallography or single-crystal X-ray diffraction is an analytical technique which uses the diffraction pattern produced by bombarding a single crystal with X-rays to solve the crystal structure. ...
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NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ...
 - based on silicon.
See also The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...
Mole Day is an unofficial holiday celebrated among chemists in North America on October 23, between 6:02 AM and 6:02 PM, making the date 6:02 10/23 in the American style of writing dates. ...
For information on how large numbers are named in English, see names of large numbers. ...
References and notes - ^ International Union of Pure and Applied Chemistry Commission on Physicochemical Symbols Terminology and Units (1993). Quantities, Units and Symbols in Physical Chemistry (2nd Edition). Oxford: Blackwell Scientific Publications. ISBN 0-632-03583-8. Retrieved on 2006-12-28. International Union of Pure and Applied Chemistry Commission on Quantities and Units in Clinical Chemistry; International Federation of Clinical Chemistry Committee on Quantities and Units (1996). "Glossary of Terms in Quantities and Units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)". Pure Appl. Chem. 68: 957–1000.
- ^ International Union of Pure and Applied Chemistry Commission on Atomic Weights and Isotopic Abundances (1992). "Atomic Weight: The Name, Its History, Definition and Units". Pure Appl. Chem. 64: 1535–43. Retrieved on 2006-12-28.
- ^ CODATA (2006).
- ^ How and When Did Avogadro's Name become Associated with Avogadro's Number? Jensen, William B. J. Chem. Educ. 2007 84 223. Link
- ^ Bader, Alfred; Parker, Leonard. "Joseph Loschmidt, Physicist and Chemist". Physics Today Online (March 2001). Retrieved on 2006-12-28.
- ^ National Institute of Standards and Technology (February 2006). Fundamental physical constants: Physico-chemical constants. Retrieved on 2006-12-28.
- ^ Bureau international des poids et mesures (March 2006). Unit of amount of substance (mole). Retrieved on 2006-12-28.
- ^ Had Avogadro been able to measure the Avogadro constant, he would have determined a value approximately half of that used today, as relative atomic masses at that time were determined on a scale of H2 = 1. In fact Avogadro's proposal, which implied atoms and molecules had a physical, measurable existence, was not widely accepted until after his death. See Amadeo Avogadro.
IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ...
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IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ...
Pure and Applied Chemistry (abb. ...
IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ...
Pure and Applied Chemistry (abb. ...
For the Manfred Mann album, see 2006 (album). ...
December 28 is the 362nd day of the year (363rd in leap years) in the Gregorian Calendar, with 3 days remaining. ...
CODATA (Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. ...
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December 28 is the 362nd day of the year (363rd in leap years) in the Gregorian Calendar, with 3 days remaining. ...
NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ...
For the Manfred Mann album, see 2006 (album). ...
December 28 is the 362nd day of the year (363rd in leap years) in the Gregorian Calendar, with 3 days remaining. ...
The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ...
For the Manfred Mann album, see 2006 (album). ...
December 28 is the 362nd day of the year (363rd in leap years) in the Gregorian Calendar, with 3 days remaining. ...
General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...
Amedeo Avogadro Count Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e Cerreto (August 9, 1776–July 9, 1856) was an Italian scientist, most noted for his contributions to the theory of molarity and molecular weight. ...
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