how was avagadros number determined?

Answer 1

The first person to estimate the actual number of particles in a given amount of a substance was Josef Loschmidt, an Austrian high school teacher who later became a professor at the University of Vienna. In 1865 Loschmidt used kinetic molecular theory to estimate the number of particles in one cubic centimeter of gas at standard conditions. This quantity is now known as the Loschmidt constant, and the accepted value of this constant is 2.6867773 x 1025 m-3.
The term "Avogadro number" was first used by French physicist Jean Baptiste Perrin. In 1909 Perrin reported an estimate of Avogadro number based on his work on Brownian motion--the random movement of microscopic particles suspended in a liquid or gas. In the years since then, a variety of techniques have been used to estimate the magnitude of this fundamental constant.


Accurate determinations of Avogadro number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron. The charge on a mole of electrons had been known for some time and is the constant called the Faraday. The best estimate of the value of a Faraday, according to the National Institute of Standards and Technology (NIST), is 96,485.3383 coulombs per mole of electrons. The best estimate of the charge on an electron based on modern experiments is 1.60217653 x 10-19 coulombs per electron. If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro number of 6.02214154 x 1023 particles per mole.
Another approach to determining Avogadro number starts with careful measurements of the density of an ultrapure sample of a material on the macroscopic scale. The density of this material on the atomic scale is then measured by using x-ray diffraction techniques to determine the number of atoms per unit cell in the crystal and the distance between the equivalent points that define the unit cell (see Physical Review Letters, 1974, 33, 464).

Answer 2

The first attempts were estimating the number of particles in a volume of gas at a given pressure and temperature. Later the number was refined by looking at the x-ray scattering of a titanium cube and calculating the unit cell.

The site is a good reference for the history of the number from the initial work of Josef Loschmidt to Avogadro's Hypothesis, which states "that equal volumes of gases under equal conditions of temperature and pressure contain equal numbers of molecules"

Answer 3

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.

no = RT/p, R = Nakb

hence:

Na = nop/kbT

where no is the number of particles in a given volume of an ideal gas, kb is the Boltzmann constant, and T is the Temperature.


ref: http://en.wikipedia.org/wiki/Avogadro's_number

Answer 4

Someone had a mole problem. So, they called up Avagadro at 602-1023.

Answer 5

By measuring the spacing of a crystal lattice by x-ray crystallography and measuring the atomic mass, you can determine the number of atoms or molecules needed to produce a crystal with the necessary density.

Answer 6

It was derived from the laws of how gasses behave.

http://en.wikipedia.org/wiki/Avogadro's_number