Avogadro’s Number

Introduction to Avagadro’s Number

The term “Avogadro’s number” is firstly described by a physician in French named  “Jean Baptiste Perrin”. Based on his research on Brownian motion, Perrin estimated its approx value in 1909. However, “Josef Loschmidt” became the first to estimate the correct value of particles in a given volume of any substance. 

Avogadro’s number is used to find the measurement of particles of any substance. It equals 6.022140857×1023 and is denoted by NA. Its SI unit is the reciprocal of mole. 

Avogadro’s Number 

Avogadro’s Number is the mass of one mole of any substance proportional to the substance’s molecular weight. For instance, when one oxygen atom integrates with two Hydrogen atoms, it results in one molecule of water (H2O), here one mole of an oxygen atom, O (1×6.022×1023) combined with two moles of a Hydrogen atom, H (2×6.022×1023 of H atoms) resulting one mole of H2O.

The exact value of Avogadro’s number can be calculated by the charge on a mole of electrons divided with the charge on a single electron, which approximately equals 6.02214154 x 1023 mol-1. 

Applications of Avogadro’s Number:

1. Used in Gay Lussac’s law of gaseous volumes 
2. Used in the determination of the atomicity of gasses
3. Used in the determination of the molecular formula of a gas 

SI Unit of Avogadro’s Number

The SI unit of Avogadro’s Constant is mole-1.

Definition:

One mole consists of  6.022×1023 small elementary units. This number is the fixed numerical value of the Avogadro’s constant, NA, when expressed in mole-1, hence called the Avogadro’s number. So, the reciprocal of the value of mole is Avogadro’s constant. 

Importance of Avogadro’s Number 

Avogadro’s constant is the number used to describe elementary particles, i.e. atoms, molecules or ions presented in one mole of any substance. However, Avogadro’s number is the mass of one mole of any substance proportional to the substance’s molecular weight, which is equivalent to 6.02214154 x 1023 mol-1.  But, Avogadro’s number becomes more accessible, using the collection of 6.023×1023 elementary particles. Avogadro’s number is the binding domain of chemistry which bridges the gap between huge numbers and smaller units. Avogadro’s number allows us to describe the mass of one mole of any substance in small numbers, i.e. the molecular weight. However, it also facilitates the description of ratios between reactants and products under any chemical reaction or equation. This is very helpful in simplifying large computations. However, it also depicts the relation between several physical constants in science. For instance, 

• It describes the relation of the atomic mass unit  with molar mass constant Mu, which is 1u=Mu/NA
• It describes the relation of   Faraday constant F with the elementary charge e, which is F=NA.e
• It describes the relationship between relative molecular mass and vapor density.
• It also describes the relationship between the gas constant R and the Boltzmann constant kB = R/NA

Along with this, the measurement of atomic level substances is based on atomic mass units. However, the Atomic mass unit can be described as the 1/12th part of the mass of one C atom.

For instance, the atomic mass unit Oxygen is equivalent to 15.999 amu. Here, the calculation of the role of any single particle, i.e. atom or electron, in a reaction is not possible. So, Avogadro’s number links atomic mass units and grams:

1 amu = 1.66 x 10-24 grams

Through this, the conversion of smaller units to gram and gr to smaller units is possible. And, the atomic mass unit of any smaller unit can be calculated easily. 

How to determine Avogadro’s Number?

To determine Avogadro’s number precisely, we need to consider both the atomic and macroscopic scales having the same unit of any single quantity. This comes into the introduction when the American physicist Robert Millikan measures the charge on one electron of an atom. However, this charge on electrons is known as the Faraday constant, 96,485.3383 C/mol. 

Although, the best way to determine the charge on an electron is 1.60217653 x 10-19 C/e–. So, by dividing the charge on a mole of electrons with the charge on one electron, Avogadro’s number can be easily calculated. 

The value of Avogadro’s Number can also be determined on the microscopic level using the density of an ultrapure sample of any material. 

The x-ray diffraction technique is used to know the number of atoms in one unit cell and the distance between the two distinctive cells of the crystal, which gives the density of the specific material on an atomic level. 

And Avogadro’s number can be determined using the formula, 

N = NA x d x V / MM

Or,

 NA = N x MM / d . V 

Where-

N = number of atoms

NA = avogadro number

d = density

V = volume

MM = molecular mass 

Avogadro’s Constant in day-to-day life 

Some examples of the concept Avogadro’s Constant, used in everyday’s life. 

• The weight of the balloon filled with helium gas is always less than the weight of a balloon filled with air. However, both the balloons consist of the equivalent number of molecules. It is because the atoms of Helium have lower atomic mass compared to the oxygen molecules or nitrogen molecules which we blow in the balloon through our mouth. That’s why the balloon of Helium gas is lighter. 
• When a human being inhales air, the volume of the lungs expands and increases due to the addition of moles of gas; similarly, when we exhale, the moles of gas are released, and the lungs get shrunk.

Conclusion 

Avogadro’s number or Avagadro’s constant, a conjecture in the science field that, If different gases of same volume kept on the same pressure or the same temperature, the number of particles remains constant in both. It describes the number of units in one mole of any substance having a molecular weight in grams. These units depend on the nature of the material used in the reaction, and it may be atoms, ions, electrons or molecules.