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Lecture 4
Nomenclature
Tutorial
1) Write ionic formulas for the following compounds:
a. Calcium Bromide
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion).
Ca2+ Br –
Step 2) Criss-cross the charges
CaBr2
b. Potassium Phosphide
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion).
K+ P 3–
Step 2) Criss-cross the charges
K3 P
c. Iron (III) Oxide
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion). Iron (III) means Fe3+.
Fe3+ O2–
Step 2) Criss-cross the charges
Fe2O3
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d. Iron (II) Oxide
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion). Iron (II) means Fe2+.
Fe2+ O2–
Step 2) Criss-cross the charges
Step 3) Reduce to smallest whole number ratio of one ion to the other
In this case the ratio of 2:2 becomes 1:1. We do NOT write Fe2O2.
FeO
e. Magnesium Hydroxide
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion).
Mg2+ OH–
Step 2) Criss-cross the charges
Step 3) When a polyatomic ion is assigned a coefficient that is greater than 1,
parenthesis must be drawn around that polyatomic ion.
Mg(OH)2
This tells us that one formula unit contains one magnesium atom, two oxygen atoms,
and two hydrogen atoms.
f. Nickel (III) Sulfate
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion). Nickel (III) means Ni3+.
Ni3+ SO42–
Step 2) Criss-cross the charges
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Step 3) When a polyatomic ion is assigned a coefficient that is greater than 1,
parenthesis must be drawn around that polyatomic ion.
Ni2(SO4)3
This tells us that one formula unit contains two nickel atoms, three sulfur atoms,
and twelve oxygen atoms.
g. Calcium Sulfate
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion).
Ca2+ SO42–
Step 2) Criss-cross the charges
Step 3) Reduce to smallest whole number ratio of one ion to the other
In this case the ratio of 2:2 becomes 1:1. We do NOT write Ca2(SO4)2.
CaSO4
We do not add parenthesis, as there is only one sulphate ion in one formula unit of
this compound.
h. Zinc Chloride
Step 1) Write the ions and their charges
The anion (negative ion) follows the cation (positive ion).
Zn2+ Cl–
The zinc ion always has a charge of 2+.
Step 2) Criss-cross the charges
ZnCl2
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