Avogadro’s Number: Definition, Value, Meaning, Unit and Symbol

Avogadro’s Number Value: While solving numerical Physics and Chemistry one name that you must have encountered in Avogardo’s number. Most of you might be aware of its usage and value; if not, then refer to this explainer. Avogadro's number is a fundamental constant in chemistry and physics that represents the number of constituent particles (usually atoms or molecules) in one mole of a substance. To know more, read further.

Avogadro’s Number

From here, you will learn the basic details about Avogadro’s number that will help you during your exams to calculate the right answer.

Avogadro’s Number Definition

Avogadro’s number, denoted as N_A, is defined as the number of constituent particles that include atoms, molecules, ions, etc. per mole of the substance. This helps in diving deep into the world of atoms and molecules and calculating them in grams and moles.

Avogadro’s Number Value

The accepted value of Avogadro's Number is approximately 6.022×10²³ particles per mole. This value is an essential part of the International System of Units (SI) and is fundamental in defining the mole, which is the SI unit for the amount of substance.

Avogadro’s Number Meaning

Avogadro’s number is a bridge that fills the gap between the atomic or molecular scale and the macroscopic scale. It helps in knowing the number of atoms/molecules present in one mole of a substance. For example, in one mole of carbon atoms (12 grams of carbon), there are 6.022×10²³ carbon atoms.

Avogadro’s Number Unit and Symbol

The unit of Avogadro's Number is particles per mole, often written as mol⁻¹. The symbol used for Avogadro's Number is N_A.

Avogadro’s Number Importance

Avogadro's Number is essential in various fields of science, including chemistry, physics, and biology. It allows scientists to quantify and relate the number of particles to measurable quantities such as mass and volume. This makes it possible to perform calculations that help in concluding the macroscopic observations.

Avogadro’s Number History

The concept is named after Italian scientist Amedeo Avogadro ((1776-1856), who proposed in 1811 that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules, regardless of their chemical nature and physical properties. Avogadro's hypothesis laid the groundwork for the development of Avogadro's Number as a fundamental constant.

Formulas With Avogadro’s Number

Some of the formulas in Chemistry and Physics that directly require Avogadro’s number are given here.

Chemistry:

• Molar Mass Calculation: Molar mass=Atomic or molecular mass×N_A

• Example: The molar mass of water (H₂O) is 18 u×N_A​.

• Number of Particles (Atoms/Molecules/Ions): Number of particles=Number of moles×N_A

• Example: The number of atoms in 1 mole of carbon (12 grams of carbon) is N_A​.

Physics:

• Ideal Gas Law: PV=nRT

• P is pressure,
• V is volume,
• n is the number of moles,
• R is the gas constant,
• T is temperature in Kelvin.

Here, n is directly related to the number of gas molecules, n=N/N_A  where N is the number of molecules.

• Boltzmann Constant: k_B=R/N_A

 Where k_B is the Boltzmann constant and R is the gas constant.

• The relationship between the Faraday constant F and the elementary charge e: F=N_Ae

Example

Calculate the molar mass of oxygen gas (O₂).

Solution:

• Atomic mass of oxygen (O) = 16 u (atomic mass units).
• Molar mass of O₂ = 2 × atomic mass of O = 2 × 16 u = 32 u.

To find the molar mass in grams per mole, we use Avogadro's Number:

• Molar mass in grams per mole = 32 u × N_A​
• N_A​ = 6.022×10²³particles per mole.

So, molar mass of O₂ = 32 u × 6.022×10²³ particles per mole = 32×1.66054×10⁻²⁴g

References and Further Reading

• Books

NCERT Class 10 Science Textbook PDF

NCERT Class 12 Physics Textbook PDF

• Articles

Magnetic effects of Electric Current

• Online Resources

CBSE Class 10 Science Video Tutorials

CBSE Class 12 Physics Video Tutorials

Also Check:

• CBSE Class 10 Science Syllabus 2024-25: Download PDF
• CBSE Class 12 Syllabus 2024-25 PDF (All Subjects)
• CBSE Class 11 Syllabus 2024-25: Latest and Revised PDF