Chemical Formulas & Counting Atoms Practice!
CHEMICAL FORMULA: short hand way of describing a molecule’s chemical structure- what elements make it
up and the number of atoms of each different element.
H2O
Subscript: number of atoms of
Coefficient: number of
the element ; equals 1 if there is
molecules of the compound;
Ca(OH)2
no other subscript
multiplies everything
2 FeBr3
Step by Step guide to counting the atoms in a chemical formula.
*Note: not all chemical formulas will need every step!
H2O
Pb(NO3)2
2 KNO3
1. Identify all elements in the molecule
H
O
Pb
N
O
K
N
O
2. Count the number of atoms of each element based on the
subscript
H= 2
O= 1
Pb= 1
N= 1
O= 3
K= 1
N= 1
O= 3
3. Get rid of parentheses by multiplying the number of atoms of
each element INSIDE the parentheses by the subscript
OUTSIDE the parentheses
H= 2
O= 1
Pb= 1
K= 1
N= 1 x 2 = 2 N= 1
O= 3 x 2 = 6 O= 3
4. Multiply the number of atoms of ALL elements by the
coefficient
H= 2
O= 1
Pb= 1
N= 2
O= 6
K= 1 x 2 = 2
N= 1 x 2 = 2
O= 3 x 2 = 6
TOTALS
H= 2
O= 1
Pb= 1
N= 2
O= 6
K= 2
N= 2
O= 6
3 Mg(OH)2
Chemical Formulas & Counting Atoms Practice!
CHEMICAL FORMULA: short hand way of describing a molecule’s chemical structure- what elements make it
up and the number of atoms of each different element.
H2O
Subscript: number of atoms of
Coefficient: number of
the element ; equals 1 if there is
molecules of the compound;
Ca(OH)2
no other subscript
multiplies everything
2 FeBr3
Step by Step guide to counting the atoms in a chemical formula.
*Note: not all chemical formulas will need every step!
H2O
Pb(NO3)2
2 KNO3
1. Identify all elements in the molecule/compound
H
O
Pb
N
O
K
N
O
2. Count the number of atoms of each element based on the
subscript
H= 2
O= 1
Pb= 1
N= 1
O= 3
K= 1
N= 1
O= 3
3. Get rid of parentheses by multiplying the number of atoms of
each element INSIDE the parentheses by the subscript
OUTSIDE the parentheses
H= 2
O= 1
Pb= 1
K= 1
N= 1 x 2 = 2 N= 1
O= 3 x 2 = 6 O= 3
4. Multiply the number of atoms of ALL elements by the
coefficient
H= 2
O= 1
Pb= 1
N= 2
O= 6
K= 1 x 2 = 2
N= 1 x 2 = 2
O= 3 x 2 = 6
TOTALS
H= 2
O= 1
Pb= 1
N= 2
O= 6
K= 2
N= 2
O= 6
3 Mg(OH)2
PRACTICE: Count the number of atoms of each element in the compound.
1. C10H14N2 (nicotine in cigarettes): C = _________ H = ___________ N = ________
2. C6H8O7 (citric acid in orange, lemon): C= _______ H= ________ O = _________
3. H3PO4 (phosphoric acid in soda) : H = ________ P= _________
O = _________
4. 2 C2H4O2 (acetic acid/vinegar) : H = _______ C = _________ O = ___________
5. H2CO3 (carbonic acid in soda) : H = ________ C = __________ O = _____________
6. 5 H2SO4 (sulfuric acid in car batteries) : H= ________ S = ____________ O = ___________
7. Al2(SO4)3 (water purification): Al= ________ S = ____________ O = _____________
8. 3 Ca(OH)2 (calcium hydroxide- sewage treatment) : Ca= ________ O = _________ H = _________
9. 4 CH4 (methane, flammable gas) : C = ___________ H = ___________
10. (NH4)2SO4 (ammonium sulfate- fertilizer) : N= _______ H = _______ S =________ O= ________
11. C18H27NO2 (capsaicin in chili pepper): C= ______ H = ______ N = ________ O = ________
12. C2952 H4664 N812 O832 S8 Fe4 (hemoglobin in blood) : C = _____________
PRACTICE: Count the number of atoms of each element in the compound.
1. C10H14N2 (nicotine in cigarettes): C = _________ H = ___________ N = ________
2. C6H8O7 (citric acid in orange, lemon): C= _______ H= ________ O = _________
3. H3PO4 (phosphoric acid in soda) : H = ________ P= _________
O = _________
4. 2 C2H4O2 (acetic acid/vinegar) : H = _______ C = _________ O = ___________
5. H2CO3 (carbonic acid in soda) : H = ________ C = __________ O = _____________
6. 5 H2SO4 (sulfuric acid in car batteries) : H= ________ S = ____________ O = ___________
7. Al2(SO4)3 (water purification): Al= ________ S = ____________ O = _____________
8. 3 Ca(OH)2 (calcium hydroxide- sewage treatment) : Ca= ________ O = _________ H = _________
9. 4 CH4 (methane, flammable gas) : C = ___________ H = ___________
10. (NH4)2SO4 (ammonium sulfate- fertilizer) : N= _______ H = _______ S =________ O= ________
11. C18H27NO2 (capsaicin in chili pepper): C= ______ H = ______ N = ________ O = ________
12. C2952 H4664 N812 O832 S8 Fe4 (hemoglobin in blood) : C = _______________