Amedeo Avogadro Full Name

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5. Amedeo Avogadro Discovery
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Amedeo Avogadro was born on August 9th 1776 to Filippo Avogadro and Anna Maria Vercellone. Coming from a family of lawyers, Advogadro was guided to a legal career, and became a bachelor of jurisprudence in 1792. Despite a successful legal career; Avogadro has started private studies of mathematics and physics, which then he pursued full time. Amedeo Avogadro. What else did he do other than be a physicist? He was a lawyer. He published in what subjects? Physics and Chemistry. Lorenzo Romano Amedeo Carlo Avogadro; Subjects. Arts and Humanities.

07th May 2019 @ 12 min read

The Avogadro constant or (the Avogadro number earlier) is the number of elementary units in one mole of any substance. The Avogadro constant is denoted as N_A. It has the dimension of the reciprocal amount of substance (mol⁻¹). The approximate value of N_A is 6.022 × 10²³ mol⁻¹. This means one mole of any substance contains 6.022 × 10²³ elementary particles. The Avogadro constant is named after Italian scientist Amedeo Avogadro.

These elementary units in one mole can be anything like atoms, molecules, ions, electrons, protons, neutrons, particles of sand. So, when we say one mole of sodium chloride, it means 6.022 × 10²³ molecules of sodium chloride.

Values of Avogadro's Constant

The value of the Avogadro constant is revised over a period of time. As of the 2019 redefinition of the SI base units, the value of the Avogadro constant is fixed to 6.02214076×1023mol−1. This is the exact value of the constant. The table below mentions the value of the constant in different units.

History of Avogadro's Constant

The Avogadro constant has a long history. The constant is named in honour of Avogadro, but he did not discover it. In 1811, Avogadro discovered the relationship between the volume of gas and the amount of gas through his experiments. He was the first to proposed the volume of a gas is directly proportional to the amount of the gas at constant pressure and temperature. This is today we call Avogadro's law or Avogadro's hypothesis. His work does not mention Avogadro's constant.

Perrin's Work

French Nobel Laureate Jean Baptiste Perrin estimated the Avogadro number with several methods. And he credited the naming of the number to Avogadro in 1909. Perrin named the number Avogadro's number, not Avogadro's constant. This name had continued till 1971. In 1971, the International System of Unit (SI) introduced a new quantity called Avogadro's constant. The Avogadro constant has the same numerical value as the Avogadro number, but they differ in the unit which will be explained later in this article.

Perrin defined the Avogadro number as the number of atoms in one gram of hydrogen (one gram-molecule). This definition was later revised to the number of atoms in 12 grams of carbon-12 (¹²C).

Loschmidt's Estimation

Before Perrin, Loschmidt also made a significant contribution to the number. Josef Loschmidt was an Austrian scientist who is notable for his work on estimation of the diameter of the molecules in the air. Through his method, it is possible to calculate the number density (the number of molecules or atoms per unit volume). This quantity is closely relative to the Avogadro constant. The relationship between them is discussed later in this article. The number density of an ideal gas is called as the Loschmidt constant. In many of German literature, these two constants are interchangeable. They can easily be distinguished from their units. The Avogadro constant is also denotated as L in honour of Loschmidt.

Other Efforts

Robert Millikan was an American physicist and Nobel Laureate. He successfully measured the charge on an electron in 1910. The electric charge per mole (the Faraday constant) of electrons had already known at that time. With the help of these two quantities, the electric charge on an electron and the Faraday constant, it is possible to calculate the number of electrons per mole. The value of this number of electrons per mole is the same as Avogadro's constant.

One of a modern method to estimate the value of the constant is X-ray crystallography. This method estimates the constant by determining the number of silicon atoms in a crystal cell, the volume per unit cell, and the molar volume.

The measurement of the accurate value of the Avogadro's constant is always troublesome. Over the period, the new methods were developed, and the Avogadro constant has continuously been improvised. From 2019, the international committee fixed the value of the Avogadro's constant exactly to 6.022 140 76 × 10²³ mol⁻¹.

2019 Redefinition and Prior Definition of Avogadro's Constant

As discussed above, the 2019 redefinition of the Avogadro constant is 6.022 140 76 × 10²³ mol⁻¹. The consequence of this redefinition is the prior definition of the constant is no longer valid. Before the 2019 redefinition, the value of the constant was defined as the amount of atoms presents in 12g of carbon-12 (¹²C). Also, because of the definition the molar mass constant (M_u) is no longer exactly equal to 1 g mol⁻¹. Instead, it is approximately equal to 1 g mol⁻¹. This is summarised in the table below.

Note: The difference in the value of the Avogadro constant before and after the 2019 definition is very small. The redefinition would not affect most of the calculations unless the high degree of precision is needed. For practical calculations, we can take N_A = 6.022 × 10²³ mol⁻¹.

Avogadro's Constant and Mole

The Avogadro constant and the mole are related quantities. In fact, the Avogadro constant is defined in terms of the mole. The value of Avogadro's constant is the number of elementary units in one mole of any substance. The definition is universally true. The below equation establishes the relation between both.

Avogadro's Constant and Molar Mass

We can use the Avogadro constant to determine the mass of any atom if we know the molar mass of that atom. This statement is also true for molecules. The molar mass is the mass of one mole of a given sample. It is expressed in g mol⁻¹. The relation between both is as follows:

where m_i is the mass of atom i and M_i is molar mass of atom i.

Avogadro's Constant and Avogadro's Number

The Avogadro constant and the Avogadro number have the same numerical value. They only differ in the unit. The Avogadro number is a dimensionless quantity, but the Avogadro constant has the dimension of the reciprocal amount of substance (mol⁻¹). The below table describes the same.

Avogadro's Constant and Boltzmann's constant

The Boltzmann constant is an important physical constant which plays a vital role in classical statistical mechanics. It is denoted as k_B or simply k. The Avogadro constant is related to the Boltzmann constant by the gas constant R.

Avogadro's Constant and Loschmidt's Constant

The Loschmidt constant is the number density (the number of molecules per unit volume). For an ideal gas, the relationship between the Loschmidt constant and the Avogadro constant at STP (P₀ = 1 atm, T₀ = 273.15 K) is described in the equation below.

Avogadro's Constant and Faraday's Constant

The Faraday constant (F) is the Avogadro constant times the elementary charge (e).

Avogadro's Constant and Unified Mass Unit

The unified mass unit or the dalton (u) is the ratio of the molar mass constant (M_u) and the Avogadro constant.

where m_u is the atomic mass constant.

The value precise value of M_u is 0.999 999 999 65(30) g mol⁻¹. But for practical purposes, we can say M_u ≈ 1 g mol⁻¹.

Examples

Example 1: To Determine Calcium Atoms

Statement: For 100 g of calcium in a beaker, calculate the number of calcium atoms in the beaker?

Solution: The molecular weight of calcium is 40.1 g mol⁻¹. The number of moles of calcium in the beaker is

The number of calcium atoms in the beaker is calculated as:

Amedeo Avogadro Full Name Definition

Therefore, the number of calcium atoms is 1.50 × 10²⁴.

Example 2: To Determine Total Molecules in Sodium Chlorine Solution

Statement: Consider 50.0 g of NaCl is dissolved in 200 g of water. Estimate the total molecules in the solution?

Solution: The molecular weight of NaCl and water is 58.44 g mol⁻¹ and 18.01 g mol⁻¹.

The moles of NaCl in 50.0 g:

The moles of H₂O in 100 g:

When 1 mol of NaCl dissociates, 1 mol of Na⁺ and 1 mol of Cl⁻ are formed. So, when 0.855 5 mol of NaCl dissociates, 0.855 5 mol of Na⁺ and 0.855 5 mol of Cl⁻ are formed.

Thus, the total number of moles after the dissociation is the sum of the moles of Na⁺, Cl⁻, and H₂O.

The total number of molecules in the solution is

Therefore, the total number of moles in NaCl solution is 4.374 × 10²⁴ mol.

Example 3: To Determine Mass of Sodium Atom

Statement: The molar mass of sodium-23 is 22.989 g mol⁻¹. Calculates the mass of a sodium atom?

Amedeo Avogadro Full Name Actor

Solution: Let m_Na and M_Na be the atomic mass and molar mass of sodium-23. Thus, M_Na = 22.989 g mol⁻¹.

Now, m_Na can be determined using the formula below.

Therefore, the mass of a sodium-23 atom is 3.817 × 10⁻²³ g.

Example 4: To Determine Molecular Mass of Iodine gas

Statement: The atomic mass of iodine is 126.9 g mol⁻¹. Determine the molecular mass of iodine gas?

Solution: The iodine gas is a diatomic gas. The molecular formula is I₂. So, the molar mass of I₂ is twice the molar mass of I.

Now, m_I2 can be determined as:

Therefore, the mass of a iodine molecule is 4.208 × 10⁻²² g.

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