The Mole

Different atoms have different masses.

1g of carbon has far fewer atoms than 1g of hydrogen atoms.

Chemists need a method of quantifying atoms.

We use a quantity called the amount of substance which is measured in moles.

One mole contains 6.02 x 1023 particles.

The relative atomic mass is the mass of one mole of that element’s atoms.

The relative molecular mass is the mass of one mole of molecules

  • 1 mole of oxygen contains 6.02 x 1023 oxygen atoms.
  • 1 mole of carbon molecules contains 6.02 x1023 carbon molecules.
  • 1 mole of electrons contains 6.02 x 1023 electrons.

Avogadro's Constant

Avogadro's constant, L, or NA is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole (mol).

Avogadro's constant is 6.02 × 1023 mol-1

 

Molar Mass

Molar mass, M, is the mass per mole of a substance.

The units of molar mass are g/mol.

 

For atoms of an element it is simply the relative atomic mass in g/mol

For sodium this is 23 g/mol.

 

For compounds it is the relative atomic masses of each atom in the formula added together.

The Molar Mass of CH4 = C + (H x 4) = 12 + (1 x 4) = 16 g/mol.

 

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