WRITING FORMULAE
GENERAL RULES:
1. When non-metals bond to form a compound, molecules are formed. The atoms in the molecule share
electrons when their orbitals with unpaired electrons overlap. These molecules are more stable than
when the atoms are separate from each other. COVALENT BONDING.
2. When a metal bonds with a non-metal, electron(s) are transferred from the metal to the non-metal to
form a positive ion (cation) and a negative ion (anion). These ions attract each other.
IONIC
BONDING.
Learn the formulas for the following molecules: (Add to the list as you come across more)
Sulphuric acid
H2SO4
Sulphur dioxide
SO2
Nitric acid
HNO3
Ammonia
NH3 (Don’t confuse with ammonium ion NH4+)
Hydrochloric acid
HCl
Carbon tetrachloride CCl4
Carbonic acid
H2CO3
Carbon monoxide
CO
Sulphurous acid
H2SO3
Water
H2O
Phosphoric acid
H3PO4
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______________________________
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Diatomic Molecules: There are 7 elements that are MOLECULES in their PURE/UNCOMBINED state:
Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Fluorine(F2), Chlorine (Cl2), Bromine (Br2), Iodine (I2).
Draw the Aufbau diagram for each of these elements to see why they would be more stable when bonded as a
molecule.
NB: THEY ARE ONLY DIATOMIC WHEN THEY ARE PURE.
The following rules apply to IONIC BONDING:
1. Group 1 elements become +1.
E.g. Na+1. We don’t write the “1”. (Li+, K+).
2. Group 2 elements become +2.
E.g. Mg+2, Ca+2 (Write +2 or 2+).
3. Group 3 elements become +3.
E.g. Al+3.
4. Group 4 elements: You will not have to give them charges.
5. Group 5 elements become -3:
E.g. N-3.
6. Group 6 elements become -2.
E.g. O-2, S-2.
7. Group 7 elements become -1.
E.g. F-, Cl-, Br-, I-. (Don’t write the “1”).
8. Group 8/0 elements do not bond. They are stable → Noble gases. (He, Ne, Ar).
9. Transition elements (between groups 2 and 3) have a charge of +2, except silver (Ag+).
Cu+2, Pb+2, Sn+2, Zn+2.
10. Stock notation:
When charges are given as Roman numerals.
E.g.
Iron(II)chloride
Fe+2 bonds to a chloride ion Cl- _______________(formula)
Lead(IV)oxide
Pb+4 bonds to an oxide ion O2_______________________(formula)
The Stock notation charges ARE ALWAYS POSITIVE and they can be given to metals and non-metals.
You will only use this method with non-metals in grade 11.
You have to know the formulae for the following polyatomic ions too:
acetate CH3COO-
When the name of a compound ends with “–ide”, e.g. sodium chloride, magnesium nitride,
hydrogen sulphide, the “ide” part comes from the Periodic Table and is NOT a polyatomic ion.
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The aim is to make the formula neutral.
No + or – signs in the formula.
Put polyatomic ions in brackets when more than one is needed.
The positive ion is written first.
Examples:
1) Calcium sulphate: Ca2+ and SO42-. Need one of each ion to make it neutral.
Formula: CaSO4.
2) Aluminium hydroxide: Al+3 and OH-. Need 3 OH- ions to cancel the +3 on the Al+3.
Formula: Al(OH)3.
3) Hydrogen sulphide: H+ and S-2. Need 2 H+ ions to cancel the -2 of S2- ion.
Formula: H2S.
4) Ammonium carbonate: NH4+ and CO32-. Need 2 NH4+ ions to cancel the -2 in CO32- ion.
Formula: (NH4)2CO3.
Ionic Compound Formula Writing Worksheet
Write chemical formulas for the compounds in each box. Example: The first box is the intersection
between the “zinc” cation and the “chloride” anion, so you should write “ZnCl2”, as shown.
chloride
acetate
nitrate
oxide
nitride
sulfate
zinc
ZnCl2
iron (II)
iron (III)
gallium
silver
lead (IV)
Write the formulas for the following compounds:
1)
copper (II) chloride ____________________________________
2)
lithium acetate ____________________________________
3)
vanadium (III) oxide ____________________________________
4)
manganese (IV) nitride ____________________________________
5)
beryllium oxide ____________________________________
6)
sodium sulfate ____________________________________
7)
aluminum arsenide ____________________________________
8)
potassium permanganate ____________________________________
9)
chromium (VI) cyanide ____________________________________
10)
tin (II) sulfite ____________________________________
11)
vanadium (V) fluoride ____________________________________
12)
ammonium nitrate ____________________________________
Chemical Formula Writing Worksheet Solutions
Write chemical formulas for the compounds in each box.
zinc
ZnCl2
iron (II)
FeCl2
iron (III)
FeCl3
gallium
GaCl3
silver
AgCl
lead (IV)
PbCl4
chloride
acetate Zn(C2H3O2)2 Fe(C2H3O2)2 Fe(C2H3O2)3 Ga(C2H3O2)3 Ag C2H3O2 Pb(C2H3O2)4
nitrate Zn(NO3)2 Fe(NO3)2 Fe(NO3)3 Ga(NO3)3 AgNO3 Pb(NO3)4
ZnO
FeO
Fe2O3
Ga2O3
Ag2O
PbO2
oxide
Zn3N2
Fe3N2
FeN
GaN
Ag3N
Pb3N4
nitride
Fe
(SO
)
Ga
(SO
)
Pb(SO
2
4 3
2
4 3
4)2
ZnSO4
FeSO4
Ag2SO4
sulfate
Write the formulas for the following compounds:
1)
copper (II) chloride CuCl2
2)
lithium acetate LiC2H3O2
3)
vanadium (III) oxide V2O3
4)
manganese (IV) nitride Mn3N4
5)
beryllium oxide BeO
6)
sodium sulfate Na2SO4
7)
aluminum arsenide AlAs
8)
potassium permanganate KMnO4
9)
chromium (VI) cyanide Cr(CN)6
10)
tin (II) sulfite SnSO3
11)
vanadium (V) fluoride VF5
12)
ammonium nitrate NH4NO3
Names & Formulas for Ionic Compounds
Give the name or formula of the following ionic compounds:
21)
sodium phosphide _____________
22)
magnesium nitrate _____________
1)
Na2CO3 ____________________
23)
lead (II) sulfite _________________
2)
NaOH ______________________
24)
calcium phosphate _____________
3)
MgBr2 ______________________
25)
ammonium sulfate _____________
4)
KCl ________________________
26)
silver cyanide _________________
5)
FeCl2 _______________________
27)
aluminum sulfide ______________
6)
FeCl3 _______________________
28)
beryllium chloride ______________
7)
Zn(OH)2 _____________________
29)
copper (I) arsenide _____________
8)
Be2SO4 _____________________
30)
iron (III) oxide _________________
9)
CrF2 ________________________
31)
gallium nitride _________________
10)
Al2S3 _______________________
32)
iron (II) bromide _______________
11)
PbO ________________________
33)
vanadium (V) phosphate ________
12)
Li3PO4 ______________________
34)
calcium oxide _________________
13)
Cu2CO3 ______________________
35)
magnesium acetate ____________
14)
Co3N2 ______________________
36)
aluminum sulfate ______________
15)
Mg3P2 ______________________
37)
copper (I) carbonate ____________
16)
Ga(NO2)3 ____________________
38)
barium oxide __________________
17)
Ag2SO3 ______________________
39)
ammonium sulfite ______________
18)
NH4OH ______________________
40)
silver bromide _________________
19)
Al(CN)3 ____________________
20)
Be(CH3COO)2 ________________
Naming Ionic Compounds – Answer Key
1)
Na2CO3
sodium carbonate
2)
NaOH
sodium hydroxide
3)
MgBr2
magnesium bromide
4)
KCl
potassium chloride
5)
FeCl2
iron (II) chloride
6)
FeCl3
iron (III) chloride
7)
Zn(OH)2
zinc hydroxide
8)
Be2SO4
beryllium sulfate
9)
CrF2
chromium (II) fluoride
10)
Al2S3
aluminum sulfide
11)
PbO
lead (II) oxide
12)
Li3PO4
lithium phosphate
13)
Cu2CO3
copper(I)carbonate
14)
Co3N2
cobalt (II) nitride
15)
Mg3P2
magnesium phosphide
16)
Ga(NO2)3
gallium nitrite
17)
Ag2SO3
silver sulfite
18)
NH4OH
ammonium hydroxide
19)
Al(CN)3
aluminum cyanide
20)
Be(CH3COO)2
beryllium acetate
21)
sodium phosphide
Na3P
22)
magnesium nitrate
Mg(NO3)2
23)
lead (II) sulfite
PbSO3
24)
calcium phosphate
Ca3(PO4)3
25)
ammonium sulfate
(NH4)2SO4
26)
silver cyanide
AgCN
27)
aluminum sulfide
Al2S3
28)
beryllium chloride
BeCl2
29)
copper (I) arsenide
Cu3As
30)
iron (III) oxide
Fe2O3
31)
gallium nitride
GaN
32)
iron (II) bromide
FeBr2
33)
vanadium (V) phosphate
V3(PO4)5
34)
calcium oxide
CaO
35)
magnesium acetate
Mg(CH3COO)2
36)
aluminum sulfate
Al2(SO4)3
37)
copper (I) carbonate
Cu2CO3
38)
barium oxide
BaO
39)
ammonium sulfite
(NH4)2SO3
40)
silver bromide
AgBr
Polyatomic Ionic Formulas Worksheet
IONS
nitrate
sulfate
sodium
NaNO3
Na2SO4
silver
ammonium
mercury(I)
zinc
calcium
magnesium
copper(I)
lead(II)
aluminum
manganese(III)
cobalt(III)
copper (II)
iron (III)
lead (IV)
potassium
barium
carbonate
phosphate
hydroxide
chromate
Polyatomic Ionic Formulas Worksheet
IONS
nitrate
sulfate
carbonate
phosphate
hydroxide
chromate
sodium
NaNO3
Na2SO4
Na2CO3
Na3PO4
NaOH
Na2CrO4
silver
AgNO3
Ag2SO4
Ag2CO3
Ag3PO4
AgOH
Ag2CrO4
ammonium
NH4NO3
(NH4)2SO4
(NH4)2CO3
(NH4)3PO4
NH4OH
(NH4)2CrO4
mercury(I)
HgNO3
Hg2SO4
Hg2CO3
Hg3PO4
HgOH
Hg2CrO4
zinc
Zn(NO3)2
calcium
magnesium
copper(I)
lead(II)
aluminum
manganese(III)
cobalt(III)
copper (II)
iron (III)
lead (IV)
potassium
barium