1. Naming Compounds Writing Formulas and Equations
Larry Scheffler
Lincoln High School

2. Naming Compounds
The chemical formula represents the composition of each molecule.
In writing the chemical formula, in almost all cases the element farthest to the left of the periodic table is written first.
So for example, the chemical formula of a compound that contains one sulfur atom and six fluorine atoms is SF6.
If the two elements are in the same group, the symbol of the element of that is lower in the group (i.e. heavier) is written first e.g. IF3.

3. Naming Ionic Compounds
Ionic compounds are combinations of positive
and negative ions.
In writing the chemical formula, the positive ion is written first, It is then followed by the name of the negative ion.
Monatomic anions end in ide. Special endings
apply for polyatomic ions
Examples
NaCl Sodium chloride
BaF2 Barium Fluoride
ZnO Zinc Oxide

4. Names of Polyatomic Ions with Oxygen
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
NO2-
Nitrite 
NO3-
Nitrate 
PO33-
phosphite 
PO43-
phosphate 
SO32-
SO42-
sulfite 
sulfate 
Polyatomic ions usually contain oxygen in addition to another element. 
Normally, they have a negative charge. 
They end in either "ate" or "ite" depending on the number of oxygen atoms present.

5. Polyatomic Ion -- Exceptions
Most polyatomic ions contain oxygen
Their names end in “ite” or “ate”.
There are several exceptions:
OH hydroxide
CN cyanide
SCN thiocyanate

6. Elements with Multiple Cations
When an element can form more than one cation, a Roman numeral is used to distinguish the oxidation state of the compound.
Iron, Tin, Lead, Copper, and are common elements with more than one cation.
Examples
PbSO4  =  lead (II) sulfate   This compound is formed from Pb2+ and  SO42-
Pb(SO4)2 =  lead (IV) sulfate   This compound is formed from Pb4+ and  SO42-
Fe(OH)2  =  iron (II) hydroxide   This compound is formed from Fe2+ and  OH- 
Fe(OH)3  =  iron (III)  hydroxide    This compound is formed from Fe3+ and  OH-

7. Examples of Ionic Compounds
NaCl = Sodium chloride
ZnF2 = Zinc fluoride
KOH = Potassium hydroxide
Ca(NO3)2 = Calcium nitrate
BaSO3 = Barium Sulfite
Al2(SO4) 3 = Aluminum sulfate
Ca3(PO3)2 = Calcium phosphite
NH4Cl = Ammonium chloride
(NH4)2CO3 = Ammonium carbonate

8. Naming Covalent Compounds
When naming covalent compounds, the name of the first element in the formula is unchanged.
The suffix “-ide” is added to the second element.
Often a prefix to the name of the second element indicates the number of the element in the compound
Covalent molecules use prefixes; Ionic molecules use Roman Numerals (most of the time).
Examples:
SF6 – sulfur hexafluoride
P4O10 – tetraphosphorous decoxide
CO – carbon monoxide
CO2 – carbon dioxide

9. Naming Covalent Compounds
Greek Prefixes:
Mono-
Di-
Tri-
Tetra-
Penta-
Hexa-
Hepta-
Octa-
Nona-
Deca-

10. Covalent molecules with multiple possibilities
Example of exceptions:
(not normally done, but you may come across)
A Roman Numeral is used to indicate the state of the more positive element
N2O   =  Nitrogen (I) oxide   Since oxygen has a 2- charge, the nitrogen must be 1+ to  balance the charges.    Also known as dinitrogen monoxide
N2O3 =  Nitrogen (III) oxide    Since oxygen has a 2- charge, the nitrogen must be 3+ to balance the charges.  Also  known as dinitrogen trioxide

11. Binary compounds of Hydrogen
The binary compounds of hydrogen are special cases. They were discovered before a convention was adopted and hence their original names have stayed.
Water H2O is not called dihydrogen monoxide
Hydrogen forms binary compounds with almost all non-metals except the noble gases.
Examples
HF - hydrogen fluoride
HCl - hydrogen chloride
H2S - hydrogen sulfide

12. Acids
When many hydrogen compounds are dissolve in water they take on the form of an acid. Special rules apply to acids.
The “ide” suffix becomes “hydro” “-ic”,
The “ite” suffix becomes “ous”
The “ate” suffix becomes “ic”
Cl-
Chloride
HCl
Hydrochloric Acid
NO2-
Nitrite
HNO2
Nitrous Acid
NO3-
Nitrate
HNO3
Nitric Acid
SO32-
Sulfite
H2SO3
Sulfurous Acid
SO42-
Sulfate
H2SO4
Sulfuric Acid
PO33-
Phosphite
H3PO3
Phosphorous Acid
PO43-
Phosphate
H3PO4
Phosphoric Acid
CO32-
Carbonate
H2CO3
Carbonic Acid

13. Writing Formulas for Ionic Compounds
Write the positive ion (cation) first, then the negative ion.
The positive charges must balance the negative charges.
Use subscripts to show how many times each ion must appear in order for the charges to balance. A subscript is not used if the ion appears only once. (Crisscross Method)
Use parenthesis around polyatomic ions that appear more than once in the formula

14. Examples Na+ and Cl- = NaCl Zn2+ and Br- = ZnBr2 K+ and OH- = KOH
Ca2+ and OH = Ca(OH)2
Fe2+ and SO = FeSO4
Fe3+ and SO = Fe2(SO4) 3
Ca2 + and PO = Ca3(PO4)2
NH4+ and Cl = NH4Cl
NH4+ and CO = (NH4)2CO3

15. Diatomic Molecules Hydrogen Fluorine Oxygen Iodine Chlorine Bromine H2
Nitrogen F2
Fluorine O2
Oxygen I2
Iodine
Cl2
Chlorine
Br2
Bromine
Certain elements exist as diatomic molecules in nature
The “Seven at 7”
Starting at #7, in the shape of a 7 (sort of), there are 7 elements

16. Diatomic Molecules Hydrogen Have Nitrogen No Fluorine Fear Oxygen Of
Certain elements exist as diatomic molecules in nature
The “Seven at 7”
Starting at #7, in the shape of a 7 (sort of), there are 7 elements H2
Hydrogen
Have N2
Nitrogen No F2
Fluorine
Fear O2
Oxygen Of I2
Iodine
Ice
Cl2
Chlorine
Cold
Br2
Bromine
Bunnies