1. #10 Write formulas for compounds formed from these
pairs of ions:
a. Ba 2+ and S-2
Ba+2 S-2
First, crisscross the charges
to balance the negatives vs positives 2 2
Then, lower the numbers if possible
to achieve the lowest whole number
ratio
BaS
b. Li+ and O-2
Li+ O-2 2 1
Li2O

2. #10 Write formulas for compounds formed from these
pairs of ions:
c. Ca 2+ and N-3
Ca+2 N-3
First, crisscross the charges
to balance the negatives vs positives 3 2
Then, lower the numbers if possible
to achieve the lowest whole number
ratio
Ca3N2
d. Cu+2 and I-1
Cu2+ I1- 1 2
CuI2

3. a. sodium iodide b. stannous chloride Na+1 and I-1 NaI SnCl2
#11 Write formulas for these compounds:
a. sodium iodide
b. stannous chloride
stannous (unfortunately) is
the old “classical” name for
the lower of the two
charges that tin can take.
According to the chart on
p. 255, Sn (tin) can be +2
or +4 stannous is the
smaller number; +2.
The other charge, +4
would be called
stannic (no roman numbers are used
in the “classical” system)
Na+1 and I-1 1 1
NaI
Therefore, stannous
chloride is:
Sn+2 and Cl or
SnCl2

4. K2S CaI2 K+1 and S-2 Ca+2 and I-1 #11c. potassium sulfide
please note that this is sulfide which is just the
element sulfur. If it were sulfate it would be
SO If it were sulfite it would be SO3-2
K+1 and S-2
K2S
d. calcium iodide
Ca+2 and I-1
CaI2

5. (NH4)2SO3 #12 Write formulas for compounds formed
from these pairs of ions.
(NH4)2SO3
a. NH4+1 and SO3-2
Always use parenthesis when you have more than one
polyatomic ion (positive or negative) to avoid interpreting
it as 42.
b. calcium ion and phosphate ion
Ca+2 and PO4-3
Ca3(PO4)2

6. a. lithium hydrogen sulfate
#13 Write formulas for these compounds:
a. lithium hydrogen sulfate
note: you get the name for
the polyatomic anions from
the chart on p. 257
Li+1 and HSO4-1
LiHSO4
b. chromium (III) nitrite
Cr+3 and NO2-1
Cr(NO2)3
Cr(NO2)3

7. #14 Key concept: Describe how to determine
the names of binary ionic compounds.
binary ionic compounds are simply two
elements, one a cation and the other an
anion coming together to make a compound
examples: NaCl LiBr MgO etc.
The rules are:
1. put the cation first and the anion last.
2. add an –ide ending to the anion.
3. if there is more than one charge possible on the cation,
you must include a roman numeral in the name to show this:
example: iron (II) oxide is FeO
iron (III) oxide is Fe2O3

8. example: zinc chloride write down Zn and Cl
#15 Key Concept: Describe how to write the formulas
for binary ionic compounds.
Rules for writing formulas:
1. write down the correct elements
2. determine the correct charges on those
elements.
3. write a balanced compound with
lowest whole number ratios.
If you only have one
charge possibility such
as zinc (check the periodic
table if you are in doubt)
You do not need a roman
numeral!
example: zinc chloride
write down Zn and Cl
check their Zn+2 (only!) and Cl-1
charges
write the
balanced compound: ZnCl2

9. Same as binary except you just put
#16 Key concept: How do you write
the formulas and the names of compounds
with polyatomic ions?
Same as binary except you just put
in the correct name of the polyatomic
ion.
look this anion up on the chart
to get its proper name
example: Na+1 and HCO3-1
is called sodium hydrogen carbonate
NaHCO3

10. #17 Write the formulas for these binary
compounds:
a. beryllium chloride
b. cesium sulfide
c. sodium iodide
d. strontium oxide
BeCl2
Cs2S
NaI
SrO

11. Cr(NO2)3 NaClO4 Mg(HCO3)2 Ca(C2H3O2)2
#18 Write the formulas for these compounds containing
polyatomic ions.
a. chromium (III) nitrite
b. sodium perchlorate
c. magnesium hydrogen carbonate
d. calcium acetate
Cr(NO2)3
NaClO4
Mg(HCO3)2
Ca(C2H3O2)2

12. #19 Identify any incorrect formulas. Explain your answer
incorrect! Mg is +2 and SO4 is -2
so the correct formula should have been:
a. Mg2(SO4)3
MgSO4
correct! Rb is +1 and As is -3
b. Rb3As
incorrect! Be is +2 (only!) and Cl is -1
so the correct formula should have been:
c. BeCl3
BeCl2
d. NaF
correct! Na is +1 and F is -1