The document explains key concepts in stoichiometry, including atomic mass, relative atomic mass, average atomic mass, and Avogadro's number. It highlights the importance of calculating the amounts of substances before and after chemical reactions, and provides definitions for moles and representative particles. Additionally, it emphasizes that one mole of a substance contains 6.02 x 10^23 representative particles.

1. Relative Atomic Mass,
Average Atomic Mass, and
Avogadro’s Number

2. • In stoichiometry, you will be looking at the amounts of substances
before the reaction and the amount of material that is produced by
the reaction. Stoichiometry is all about number.
• In solving problems involving stoichiometry, you might be looking at
the mass of the reactants, mass of the products, chemical equations,
molecular weights and formulas.
• Atomic mass is the mass of an atom of a chemical element expressed
in atomic mass units. It is approximately equivalent to the number of
protons and neutrons in the atom (the mass number) or to the
average number allowing for the relative abundances of different
isotope. Atomic mass is expressed in amu or atomic mass units.
• Relative atomic mass is the mass of any atom obtained by
comparing it with the atomic mass of carbon-12

3. • Average atomic mass is equal to the weighted average of all isotopes
of an atom. Most elements occur in nature as a combination of
different isotopes.
• Average atomic mass is dependent on both the mass and the relative
abundance of each of the element's isotope. It can be computed using
the formula:

4. • Mole, abbreviated as mol, is the SI unit of material quantity. One mole
is the number of atoms in precisely 0.012 kg of carbon - 12. This
means that the unit mole, basically tells you how many atoms a
substance has. A representative particle can be an atom, an ion, a
molecule or a formula unit. The representative particle "atom" is used
for elements. The representative particle "molecule" is used for
covalent compounds and for diatomic elements. Diatomic elements
are elements that consist of two atoms. Diatomic elements include
hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine.
The representative particle "formula unit" is used for ionic
compounds.
• One mole of a substance contains 6.02 x 1023 representative particles.
The number 6.02 x 1023 is known as Avogadro's number. For example,
mole of iron contains 6.02 x 1023 atoms of iron 1 mole of H2O
contains 6.02 x 1023 molecules of H2O 1 mole of NaCl contains 6.02 x
1023 formula units of NaCl