#10 Write formulas for compounds formed from these
pairs of ions:
a. Ba 2+ and S-2
Ba2+2 S
-2
2
BaS
b. Li+ and O-2
Li+2 O-21
Li2O
First, crisscross the charges
to balance the negatives vs positives
Then, lower the numbers if possible
to achieve the lowest whole number
ratio
#10 Write formulas for compounds formed from these
pairs of ions:
c. Ca 2+ and N-3
Ca3+2 N
-3
2
Ca3N2
d. Cu+2 and I-1
Cu12+ I21CuI2
First, crisscross the charges
to balance the negatives vs positives
Then, lower the numbers if possible
to achieve the lowest whole number
ratio
#11 Write formulas for these compounds:
a. sodium iodide
Na+1
1
and
I-1
1
NaI
Therefore, stannous
chloride is:
Sn+2 and Cl-1 or
SnCl2
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)
#11c.
potassium sulfide
K+1 and S-2
K2S
d. calcium iodide
Ca+2 and I-1
CaI2
please note that this is sulfide which is just the
element sulfur. If it were sulfate it would be
SO4-2 If it were sulfite it would be SO3-2
#12 Write formulas for compounds formed
from these pairs of ions.
a. NH4+1 and SO3-2
(NH4)2SO3
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
#13 Write formulas for these compounds:
a. lithium hydrogen sulfate
Li+1 and HSO4-1
LiHSO4
b. chromium (III) nitrite
Cr+3 and NO2-1
Cr(NO
Cr(NO2)23)3
note: you get the name for
the polyatomic anions from
the chart on p. 257
#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
#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.
If you only have one
3. write a balanced compound with
charge possibility such
lowest whole number ratios.
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
#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
look this anion up on the chart
ion.
to get its proper name
example: Na+1 and HCO3-1
is called sodium hydrogen carbonate
NaHCO3
#17 Write the formulas for these binary
compounds:
a. beryllium chloride
BeCl2
b. cesium sulfide
Cs2S
c. sodium iodide
NaI
d. strontium oxide
SrO
#18 Write the formulas for these compounds containing
polyatomic ions.
a. chromium (III) nitrite
Cr(NO2)3
b. sodium perchlorate
NaClO4
c. magnesium hydrogen carbonate
Mg(HCO3)2
d. calcium acetate
Ca(C2H3O2)2
#19 Identify any incorrect formulas. Explain
your answer
a. Mg2(SO4)3
incorrect! Mg is +2 and SO4 is -2
so the correct formula should have been:
MgSO4
b. Rb3As
c. BeCl3
correct! Rb is +1 and As is -3
incorrect! Be is +2 (only!) and Cl is -1
so the correct formula should have been:
BeCl2
d. NaF
correct! Na is +1 and F is -1