Writing Formulas
for Binary Ionic
Compounds
The first thing we need is a couple of
definitions:
The first thing we need is a couple of
definitions:
1. When a metal combines with a nonmetal, an ionic compound is formed.
The first thing we need is a couple of
definitions:
1. When a metal combines with a nonmetal, an ionic compound is formed.
2. A binary compound consists of only
two elements.
In
Science
10, you’ll
be given
this
Periodic
Table:
In
Science
10, you’ll
be given
this
Periodic
Table:
In
Science
10, you’ll
be given
this
Periodic
Table:
See the
staircase!
In
Science
10, you’ll
be given
this
Periodic
Table:
METALS
In
Science
10, you’ll
be given
this
Periodic
Table:
METALS
NON-METALS
A binary ionic compound forms when:
A binary ionic compound forms when:
a positively charged metal ion combines with
A binary ionic compound forms when:
a positively charged metal ion combines with
a negatively charged non-metal ion.
What the formula
for an ionic
compound means.
The formula for the ionic compound
sodium chloride is NaCl.
The formula for the ionic compound
sodium chloride is NaCl.
This does NOT mean that sodium chloride
consists of individual NaCl “molecules”
like this:
The formula for the ionic compound
sodium chloride is NaCl.
This does NOT mean that sodium chloride
consists of individual NaCl “molecules”
like this:
Na
Cl
The formula for the ionic compound
sodium chloride is NaCl.
This does NOT mean that sodium chloride
consists of individual NaCl “molecules”
like this:
Na
Cl
Na+ ion
Cl– ion
Na+ ion
Cl– ion
Crystal lattice of
NaCl
Na+ ion
Cl– ion
For every Na+ ion,
there is one Cl– ion
Na+ ion
Cl– ion
The formula for an ionic compound
gives the smallest whole number ratio
of ions.
Na+ ion
Cl– ion
For every Na+ ion,
there is one Cl– ion
The formula for
sodium chloride is
Na1Cl1= NaCl
Na+ ion
Cl– ion
For every Na+ ion,
there is one Cl– ion
The formula for
sodium chloride is
Na1Cl1= NaCl
The formula for calcium fluoride is
CaF2
This means that calcium fluoride consists
of a huge pile of Ca2+ and F– ions.
CaF2
The formula for calcium fluoride is
CaF2
This means that calcium fluoride consists
of a huge pile of Ca2+ and F– ions.
CaF2
The formula for calcium fluoride is
CaF2
This means that calcium fluoride consists
of a huge pile of Ca2+ and F– ions.
CaF2
For every Ca2+ ion,
there are 2 F– ions
Finding the
formula for an
ionic compound
There are two methods that we will
show you for finding formulas.
There are two methods that we will
show you for finding formulas. Then
you can decide which method works
best for you.
There are two methods that we will
show you for finding formulas. Then
you can decide which method works
best for you. The two methods are:
There are two methods that we will
show you for finding formulas. Then
you can decide which method works
best for you. The two methods are:
1. Equalizing + and – charges
There are two methods that we will
show you for finding formulas. Then
you can decide which method works
best for you. The two methods are:
1. Equalizing + and – charges
2. Crossing down charges
Finding a formula by equalizing + and – charges
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
+3
–1
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
+3
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
+3
–3
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
+3
Add up to 0
–3
Finding a formula by equalizing + and – charges
What is the formula for aluminum bromide?
Ion Name
Ions
Total Charges
Formula
aluminum
bromide
Al3+
Br1–
Br1–
Br1–
+3
–3
AlBr3
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+2
–3
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+2
–3
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+2
–3
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+2
–3
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+6
–6
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+6
–6
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+6
–6
Ca3P2
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+6
Add up to 0
Ca3P2
–6
Finding a formula by equalizing + and – charges
What is the formula for calcium phosphide?
Ion Name
Ions
Total Charges
Formula
calcium
phosphide
Ca2+
Ca2+
Ca2+
P3–
P3–
+6
–6
Ca3P2
Finding a formula by crossing down charges
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Finding a formula by crossing down charges
What is the formula for rubidium sulphide?
1+
Rb
2–
S
Rb2S
Formula
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Both of these
numbers are
multiples of 2
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
Divide both of
these
numbers by 2
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
÷2
2–
O
V2O4
VO2
Finding a formula by crossing down charges
What is the formula for vanadium(IV) oxide?
4+
V
2–
O
V2O4
VO2
Formula