How did Avogadro discover his number?

Answer 1

The idea of Avogadro's number:

It took a lot of people a lot of time to determine Avogadro's number. It really comes out of the study of gasses which had the remarkable property that pressure, volume and temperature were very very similar for all gasses, so similar that they created something called the ideal gas law. It was Avogadro who hypothesized that two nearly-ideal gasses at the same pressure, temperature and volume had the same number of atoms or molecules. But, he did not say how many and the number is actually Avogadro's number.

Measuring Avogadro's number:

To determine Avogadro's number, the number of molecules in a standardized quantity of gas (one mole), one needs to know the mass of a molecule. There were several people and several approaches that gradually got a more and more accurate result. Here are some examples.

(a) It was known the putting current though a solution could plate out metals or generate gasses at the electrodes. Careful measurement revealed that a certain current for a certain time produced one mole of atoms. So, if one assumed that each atom needed one electron to be converted from the ionic form to the gaseous form, one only needed to know the number of electrons provided by the current. To know that, one needs the charge of the electron and physicist Robert Millikan measured that in 1910.

(b) The kinetic theory of gasses says that each molecule has a translational kinetic energy proportional to temperature. Of course, kinetic energy is also proportional to mass. Since we can not see molecules, we can not see how fast they are going. It was Einstein, in 1907, who published an explanation of Bownian motion, and deduce the mass of the molecules causing it. (Brownian motion was first observed as the random jumping of grains of pollen in 1827, the botanist Robert Brown.)

(c) French physicist Jean Perrin won the 1926 Nobel Prize in Physics, largely for his work in determining the Avogadro constant by several different methods, including some based on Einstein's calculations.

(d) X-rays were discovered in 1895 and the series of discoveries regarding x-ray diffraction continued until the realization that atoms were causing the scattering and the spacing between atoms and scattering patterns followed mathematical rules. In 1914, these rules were used to identify the structure of salt crystals (NaCl). Along the way, this research connected the wavelength of x-rays to the spacing of atoms, thus allowing one to know the number of atoms in a given volume and that also gives Avogadro's number.

It is hard to say that anyone discovered the actual value of Avogadro's number, but rather many people helped get increasingly better values of the number.

More Background:

Amedeo Avogadro did not discover Avogadro's constant. In chemistry, the quantity of a substance that equals one mole was named in honor of Avogadro, but not because he discovered it. Avogadro's number, NA (or Avogadro's constant) is approximately 6.0221415 × 1023.

Johann Josef Loschmidt is given credit for the first calculation of the value of Avogadro's number in the year 1865. Of course, the first calculation was fairly crude and many people have improved on this calculation since. Notably, Jean Baptiste Perrin received the Nobel Prize in Physics in 1926 for extensive work establishing the atomic nature of matter and that work involved experimental results that gave a reliable value for Avogadro's number.

Avogadro is given credit for Avogadro's Law which asserts that if two gases have the same temperature, volume and pressure, then the elementary entities (molecules) that make up the gasses have masses in the same proportion as the masses of the two quantities of gas. In 1811, Avogadro hypothesized this law. His work and plus the work of many others eventually led to knowing Avogadro's number which allows one to actually know the mass of the molecules in the gas, not just the ratios of masses.

The research of Avogadro, Loschmidt, Perrin, Einstein and many others was taking place in the 19th century when the idea that there were such things as atoms and molecules was still developing and these researchers are famous because they made important advancements that eventually led to the modern understanding of atoms and molecules.

Answer 2

Amedeo Avogadro did not discover Avogadro's constant. In chemistry, the quantity of a substance that equals one mole was named in honor of Avogadro, but not because he discovered it. Avogadro's number, NA (or Avogadro's constant) is approximately 6.0221415 × 1023.

Johann Josef Loschmidt is given credit for the first calculation of the value of Avogadro's number in the year 1865. Of course, the first calculation was fairly crude and many people have improved on this calculation since. Notably, Jean Baptiste Perrin received the Nobel Prize in Physics in 1926 for extensive work establishing the atomic nature of matter and that work involved experimental results that gave a reliable value for Avogadro's number.

Avogadro is given credit for Avogadro's Law which asserts that if two gases have the same temperature, volume and pressure, then the elementary entities (molecules) that make up the gasses have masses in the same proportion as the masses of the two quantities of gas. In 1811, Avogadro hypothesized this law. His work and plus the work of many others eventually led to knowing Avagadro's number which allows one to actually know the mass of the molecules in the gas, not just the ratios of masses.

The research of Avogadro, Loschmidt, Perrin, Einstein and many others was taking place in the 19th century when the idea that there were such things as atoms and molecules was still developing and these researchers are famous because they made important advancements that eventually led to the modern understanding of atoms and molecules.

Answer 3

He didn't. Avogadro's number was simply named after Avogadro.

Answer 4

He discovered the mole in 1815