Naming Ionic and Molecular Compounds and Writing Formulas
A compound is made of
two or more elements.
The name should tell
us how many and what type of atoms there are.
have already examined two types of compounds:
A. Ionic compounds
Made of cations and anions.
Metals and nonmetals.
The electrons lost by the cation are gained by the anion.
Naming Monoatomic Ions
Representative metal - if the charge is always the same (Group A)
just write the name of the metal. (It does not change)
Transition metals can have more than one type of charge. Indicate
the charge with roman numerals in parenthesis.
Write Formulas for these:
Magnesium ion Copper (II) ion
Chromium (VI) ion Barium
ion Mercury (II) ion
Change the element ending to – ide
Ie. Fluorine (F) would become Fluoride (F-1)
Write Formulas for these:
Sulfide ion Iodide
ion Phosphide ion
Naming Polyatomic Ions
Polyatomic ions are groups of atoms that stay together and have a charge.
must memorize the following common polyatomic ions:
Naming Binary Ionic Compounds
Compounds consist of 2 elements. Simply name the two ions.
1. NaCl = Na+
= sodium chloride
to first figure out their charges, then indicate the charge in brackets following
the name of the metal.
The compound must be neutral (same total number of + and – charges).
Use the anion to determine the charge on the positive ion.
Examples: Naming Binary Ionic Compounds Containing Transition
Write the name of CuO - Need the charge of Cu
- The charge of O is -2
- Therefore copper must be +2
- Name: Copper (II) chloride
2. Name CoCl3
- Cl is -1 and
there are three of them = -3
- Co must be +3
- Name: Cobalt (III) chloride
- Since S is -2, the Cu2
must have an overall charge of +2, so each ion is +1.
- Name: Copper (I) sulfide
- Each O is –2; therefore 3 x
-2 = -6 charge
- 3 Fe must = +6, so each Fe ion is +2.
- Name: Iron (III) oxide
Write the names of the following binary ionic compounds:
Naming Ternary Ionic Compounds
Compounds consist of 3 or more elements. Name the two ions. At least one of the
ions will be polyatomic – note: the suffix of the polyatomic ion does not
change. Example: K3PO3 is potassium phosphite
Write the names of the following ternary ionic
Writing Chemical Formulas
chemical formula shows the kind and number of atoms in the smallest piece of a
The overall charge of the compound is zero.
Balance the charges by adding subscripts.
Put polyatomic ions in brackets when using a subscript.
Example: Write the formula for calcium chloride.
Calcium is Ca+2,
Chloride is Cl-1,
would have a +1 charge, therefore another Cl-1
Chemical formula: CaCl2
Write the chemical formula of the following compounds:
Copper (II) sulfate
Iron (III) phosphide
Iron (III) sulfide
Things to look for
cations have brackets in the name, the number is their charge.
anions end in -ide they are probably off the periodic table (Monoatomic)
anion ends in -ate or -ite it is polyatomic
- Made of molecules.
- Made by joining nonmetal atoms together.
Naming Molecular Compounds
name of a molecular compound indicates the type and number of atoms. Prefixes
are used to tell you the number. You must memorize the following prefixes.
To name a molecular compound, write two words:
Prefix + Name of first nonmetal + Prefix + Name of second
nonmetal + ide
- don’t write mono- if there is only
one of the first element.
- don’t use the following double vowels when writing names (oa oo)
Name these molecular compounds:
Write formulas for these:
1. diphosphorus pentoxide
2. tetraiodide nonoxide
6. phosphorus trifluoride