Name:_____________________________________ Date:____________ Per.:_____
Unit 5 – Covalent Molecule Problems #3
Ionic Compound Formulas:
METAL + NON-METAL (or polyatomic ion)
Example: Iron (II) Chloride
1. Write the ions with the charges.
 Roman numeral tells you the charge of the metal
 If the ion name ends in “ate” or “ite” it is polyatomic.
 If the ion name ends in “ide” (except hydroxide, OH-, and cyanide, CN-) it is monatomic.
2. If the sum of the charges do not equal zero (0), do the cross rule to determine formula
Fe2+ Cl-
Fe 1 Cl 2
Write the formula, without charges (don’t write a 1).
FeCl 2
Use parentheses ( ) if you need more than one polyatomic ion! (ex. Mg(OH)2)
3. Check:
(a) All numbers are subscripts (on the bottom).
(b) There are no charges or Roman numerals in the formula.
Molecular Compound Formulas:
NON-METAL + NON-METAL
Example: Sulfur trioxide
1. Write the two elements side by side
SO
2. The prefixes tell you the subscripts
SO3
(No prefix on first element means the subscript is 1)
3. Check:
(a) All numbers are subscripts (on the bottom).
(b) There are no charges or Roman numerals in the formula.
(c) You did NOT use the cross rule.
Name
Beryllium fluoride
Dinitrogen trichloride
Cobalt (III) phosphide
Phosphorous disulfide
Disulfur hexafluoride
Calcium phosphate
Sodium sulfite
Nickel (II) nitrite
Ionic (I) or
Covalent (C)
Cross Rule?
(Y or N)
Formula
Check
(see above)
Ionic Compound Names:
METAL + NON-METAL (or polyatomic ion)
Example: Cu(NO3)2
1. Circle each ion.
2. Name each ion.
Cu ( NO3 )2
 Look up name of polyatomic ions on your ion list
 Monatomic anion name ends in “ide”
 Transition metals and Pb and Sn must include Roman numeral to indicate ion
charge.
Each NO3 has a -1 charge, so total negative charge is -2. Therefore, copper
must have a +2 charge:
Copper (II) nitrate
1. Check:
(a) There are NO prefixes in the name.
(b) Roman numerals shown for transition metals, Pb & Sn (but not Zn, Ag, or Cd)
Molecular Compound Names:
NON-METAL + NON-METAL
Example: N2O4
1. Use prefixes to indicate number in compound.
 If first element has a subscript of 1, don’t include the mono- prefix.
2. Name the first element. Second element, change end of name to “ide”
Dinitrogen tetroxide
3. Check:
Formula
SnO
PO3
Cr2S3
PbI4
Ag3PO4
N2O3
K2CO3
CS2
Mg(OH)2
Al2(SO3)3
(a) There are NO Roman numerals
(b) You included prefixes for all elements unless the first element has a subscript of 1.
Ionic (I) or
Covalent (C)
Prefixes?
(Y or N)
Roman
Numeral?
(Y or N)
Name
Check
(see
above)