Definition of Mole

• A mole (mol) is an SI unit used by chemists to quantify a specific number of elementary entities (atoms, molecules, ions, etc.).

• Specifically, one mole contains

  • 6.022 x 10^23 particles, known as Avogadro’s number (N_A).

• It is defined based on the number of atoms in 12 grams of carbon-12.

Difference from Other Terms

• Terms like pair (2 items) and dozen (12 items) are used in everyday life, whereas mole is specific to chemistry for counting atoms and molecules.

Avogadro’s Number

• Amadeo Avogadro (1776-1856) introduced the concept of Avogadro’s number to measure large quantities of atoms.

• Value of Avogadro's Number:

  • The number of atoms in 12 grams of carbon-12 is 6.02214076 x 10^23.

  • Usually rounded to 6.022 x 10^23.

• This number is applicable to:

  • Atoms (e.g., Pb)

  • Molecules (e.g., H2O, H2)

  • Formula Units (e.g., NaCl)

  • Ions (e.g., Na⁺ and Cl⁻)

Examples of Mole Calculation

• 1 mole of H2O = 6.022 x 10^23 molecules of H2O

• 1 mole of Na = 6.022 x 10^23 atoms of Na

Key Relationships

• A mole of a substance contains:

  • 6.022 x 10^23 particles of that substance.

  • The same number of particles as in 12 grams of carbon-12.

  • Mass equivalent to the molar mass (in grams) expressed as atomic or molecular mass of the substance.

Summary Points

• Avogadro's number signifies the massive number of particles in a mole, facilitating practical calculations in chemistry.

• Understanding the mole is fundamental to stoichiometry in chemical reactions, allowing chemists to count and relate quantities of substances in a formulaic manner.