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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 Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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 Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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 Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
+2
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
+2 for many; some +1, others +3; several vary
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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 Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
-2
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
-3
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
+2
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
+3
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
+2
+2
+1
Periodic Table of the Elements1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
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
Ag
48
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
Au
80
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
No ions for noble gases.
Combining Ions
Remember: Charges must add to zero.
Na+ with S2-
Na+ S2- Na+
Na2S
Ca2+ and Cl-1
Cl-1 Ca2+ Cl-1
CaCl2
+1 -2 +2 -1+1 -1
Combining Ions
Remember: Charges must add to zero.
Mg+2 with S2-
Mg+2 S2-
MgS
Al3+ and Br-1
+2 -2
+3 -1
-1-1
AlBr3
Br-1
Br-1
Br-1
Al3+
Combining Ions
Remember: Charges must add to zero.
Mg+2 with N3-
Mg+2 N3- Mg+2 N3- Mg+2
Mg3N2
+2 -3-3+2
+2
You Do One…
Remember: Charges must add to zero.
Ba+2 with I-
I- Ba+2 I-
BaI2
+2 -1-1
And another…
Remember: Charges must add to zero.
Al3+ with F-
AlF3+3 -1
-1-1
Again…
Remember: Charges must add to zero.
Al3+ with O2-
Al2O3+3 -2
-2-2
+3
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- Cl-
CrCl3
+3 -1-1-1
Write these formulas…
Silver oxide
+1 -2+1
Ag2O
Write these formulas…
Iron(III) iodide
+3 -1-1
FeI3
-1
Write these formulas…
Copper(II) oxide
+2 -2
CuO
Write these formulas…
Copper(I) oxide
+1 -2
Cu2O
+1
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 -2
Cu2CO3
+1
Write these formulas…
Iron(II) nitrate
+2 -1
Fe(NO3)2
-1
Write these formulas…
Ammonium phosphate
+1 -3
(NH4)3PO4
+1+1
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
