Writing Ionic Formulas
Chemical Formulas from Names
&
Names from Chemical Formulas
Basic Principles
• Formulas show smallest whole-number
ratio of ions (posititve and negative) in the
substance.
• Formulas are correct only if total charges of
all ions add to zero (bulk matter is
electrically neutral).
• Cations (positive) written and named before
anions.
Periodic Table of the Elements
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
+1
Periodic Table of the Elements
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
1
H
+2
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
2
He
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
1
H
3
Li
2
He
4
Be
+2 for many; some +1,
others +3; several vary
11 12
Na Mg
5
B
6
C
7
N
8
O
9
F
10
Ne
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
-1
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
-2
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
-3
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
35
Br
36
Kr
+2
31 32 33
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
Ga
Ge
As
34
Se
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
1
H
3
Li
2
He
+3
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Periodic Table of the Elements
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
+2
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
32
Ge
33
As
34
Se
35
Br
36
Kr
53
I
54
Xe
85
At
86
Rn
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
89
Ac
104
105
106
107
108
109
110
87
Fr
88
Ra
+1
111
112
+2
50 51
Sn
Sb
52
Te
82
Pb
83
Bi
84
Po
Periodic Table of the Elements
1
H
3
Li
2
He
No ions for
noble gases.
4
Be
11 12
Na Mg
5
B
6
C
7
N
8
O
9
F
10
Ne
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47 48
Ag Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
112
Combining Ions
Remember: Charges must add to zero.
Na+ with S2-
Ca2+ and Cl-1
Na+ S2- Na+
Cl-1 Ca2+ Cl-1
Na2S
+1 -2
+1
CaCl2
+2 -1
-1
Combining Ions
Remember: Charges must add to zero.
Mg+2 with S2Mg+2 S2MgS
+2 -2
Al3+ and Br-1
Br-1
Al3+ Br-1
Br-1
AlBr3
+3 -1
-1
-1
Combining Ions
Remember: Charges must add to zero.
Mg+2 with N3Mg+2 N3- Mg+2 N3- Mg+2
Mg3N2
+2 -3
+2 -3
+2
You Do One…
Remember: Charges must add to zero.
Ba+2 with II- Ba+2 IBaI2
+2 -1
-1
And another…
Remember: Charges must add to zero.
Al3+ with FAlF3
+3 -1
-1
-1
Again…
Remember: Charges must add to zero.
Al3+ with O2Al2O3
+3 -2
+3 -2
-2
Transition-metal Cations
• Named with positive charge as Roman
•
•
•
•
numeral
+1 = (I)
+2 = (II)
+3 = (III)
Only rarely are charges bigger than three.
Transition-metal Cations
• Several elements can, under different
conditions, form ions with different charges.
• Iron is +2 or +3, Iron(II) or Iron(III)
• Copper is +1 or +2, Copper(I) or Copper(II)
• A given ion will have only one charge; its
value depends on how the ion was formed.
Combining Ions
Rules are the same; charges add to zero.
Chromium(III) with chloride
Cr+3 Cl- Cl- ClCrCl3
+3 -1
-1
-1
Write these formulas…
Silver oxide
+1
+1
Ag2O
-2
Write these formulas…
Iron(III) iodide
+3
FeI3
-1
-1
-1
Write these formulas…
Copper(II) oxide
+2
CuO
-2
Write these formulas…
Copper(I) oxide
+1
+1
Cu2O
-2
Polyatomic Ions
•
•
•
•
•
Multi-atom Ions
Usually are negative
Usually contain oxygen
Names often end in -ite or -ate
Charges and formulas cannot be predicted
from Periodic Table
Polyatomic Ions
• Nitrate = NO3-1
– One N plus three oxygens; total charge = -1
• Carbonate = CO3-2
– One carbon plus three oxygens; total charge = -2
• Sulfate = SO4-2
– One S plus four oxygens; total charge = -2
• Hypochlorite = ClO-1
– One Cl plus one oxygen; total charge = -1
Good News!
• Same rules for writing ionic formulas using
ployatomic ions as for “simple ions”
• Charges of all ions must add to zero
Combining Ions
Rules are the same; charges add to zero.
Sodium nitrate
Na+1 and NO3-1
NaNO3
+1 -1
Combining Ions
Rules are the same; charges add to zero.
Sodium carbonate
Na+1 and CO3-2
Na2CO3
+1 -2
+1
Combining Ions
Rules are the same; charges add to zero.
Magnesium nitrate
Mg+2 and NO3-1
Mg(NO3)2
+2 -1
-1
Note: where more than one polyatomic ion occurs, it
must be enclosed in parentheses. A subscript always
follows the closed parenthesis.
Write these formulas…
Copper(I) carbonate
+1
+1
Cu2CO3
-2
Write these formulas…
Iron(II) nitrate
+2
Fe(NO3)2
-1
-1
Write these formulas…
Ammonium phosphate
+1
+1
+1
-3
(NH4)3PO4
Note, this polyatomic ion appears only
once and does not have parentheses.
Names these substances...
•
•
•
•
•
•
•
Na2SO4
Cu2S
FeS
Fe2S3
FeSO4
Mg3N2
Mg(NO3)2
Sodium sulfate
Copper(I) sulfide
Iron(II) sulfide
Iron(III) sulfide
Iron(II) sulfate
Magnesium nitride
Magnesium nitrate