Remember that ELEMENTS have only ONE type of atom (one element) in them

• Aluminum (Al)

• Gold (Au)

• Nitrogen gas (N₂) - a Molecular Element (one of the 7 diatomic elements)

• Sulfur (S₈) - molecular Sulfur, also a Molecular element

Remember that COMPOUNDS have TWO or MORE different types of atoms (elements) in them

• Aluminum Oxide (Al₂O₃)

• Copper (I) Nitrate (CuNO₃)

• Dihydrogen monoxide = water (H₂O)

• Sulfur dioxide (SO₂)

• Glucose (C₆H₁₂O₆)

Remember that when Counting atoms, you have look at the SUBSCRIPTS on each element, and pay attention to what you are being asked to count

• Aluminum Oxide (Al₂O₃) = 2 Aluminum atoms + 3 Oxygen atoms = 5 TOTAL ATOMS.... 2 different ELEMENTS

• Water (H₂O) = 2 Hydrogen atoms + 1 Oxygen atom = 3 TOTAL ATOMS.... 2 different ELEMENTS

• Glucose (C₆H₁₂O₆) = 6 Carbon atoms + 12 Hydrogen atoms + 6 Oxygen atoms = 24 TOTAL ATOMS.... 3 different ELEMENTS

If you have a chemical formula with PARENTHESES, you have to MULTIPLY EVERYTHING INSIDE the parentheses by the SUBSCRIPT on the outside of the Parenthesis.

• Copper (II) Nitrate = Cu(NO₃)₂ = Cu(NO₃)(NO₃)

• .........= 1 Copper atom + [2*1 Nitrogen atoms + 2*3 Oxygen atoms]

• .........= 1 Copper atom + [2 Nitrogen atoms + 6 Oxygen atoms]

• ........ = 9 TOTAL atoms

• ........ = 3 Different ELEMENTS

One more chemical formula with PARENTHESES:

• Magnesium Phosphate = Mg₃(PO₄)₂ = Mg₃(PO₄)(PO₄)

• ....= 3 Magnesium atoms + [2*1 Phosphorus atoms + 2*4 Oxygen atoms]

• ....= 3 Magnesium atoms + [2 Phosphorus atoms + 8 Oxygen atoms]

• .... = 13 TOTAL atoms

• .... = 3 Different ELEMENTS

The NUMBER IN FRONT of the FORMULA, is called the COEFFICIENT.

The COEFFICIENT tells us how many UNITS (molecules or formula units) we have, so MULTIPLY the COEFFICIENT by every element in the formula.

• Al₂O₃ = 2 Aluminum atoms + 3 Oxygen atoms = 5 TOTAL ATOMS

• 4 Al₂O₃ = Al₂O₃ + Al₂O₃ + Al₂O₃ + Al₂O₃

• 4 Al₂O₃ = 4*2 Aluminum atoms + 4*3 Oxygen atoms = 4*5 TOTAL ATOMS

• 4 Al₂O₃ = 8 Aluminum atoms + 12 Oxygen atoms = 20 TOTAL ATOMS

One more example with a COEFFICIENT :

Remember, we MULTIPLY the COEFFICIENT by the formula.

• Mg₃(PO₄)₂ = Mg₃(PO₄)(PO₄)

• Mg₃(PO₄)₂ = 3 Magnesium atoms + 2 Phosphorus atoms + 8 Oxygen atoms = 13 TOTAL ATOMS

• 4 Mg₃(PO₄)₂ = 4*3 Magnesium atoms + 4*2 Phosphorus atoms + 4*8 Oxygen atoms = 4*13 TOTAL ATOMS

• 4 Mg₃(PO₄)₂ = 12 Magnesium atoms + 8 Phosphorus atoms + 32 Oxygen atoms = 52 TOTAL ATOMS