1. Chemical Formulas and Chemical Compounds
Chapter 7

2. Molecular and Ionic Compounds
Molecular Compound
(Covalent)
Composition
metal-nonmetal
nonmetal-nonmetal
Smallest unit
formula unit
molecule
Smallest particles
ions
atoms

3. Significance of Chemical Formulas
Subscripts—refer only to the atom (or atoms in parentheses) that come BEFORE it
Al2(SO4)3
NOTE: multiply subscripts outside parentheses with the subscripts inside them to get the total number of each atom

4. Naming Monatomic Ions Monatomic: made up of only ONE atom
All group A (main group) monatomic CATIONS: simply name the name of the element and add “ion” to it
All monatomic anions: change ENDING to
“-ide” (NOTE: most elements lose a significant amount of their name. Ex. sulfur  sulfide; phosphorus phosphide; oxygen  oxide)

5. Naming Monatomic Ions Cont…
Stock System: uses roman numerals to indicate the positive charge an ion has
Copper (II) means Cu+2
USE THIS SYSTEM ONLY WHEN NAMING TRANSITION METAL IONS
Exceptions: Tin (Sn) and Lead (Pb) also get the roman numeral

6. Naming Monatomic Ions Cont…
Name
Stock System
Fe2+
ferrous
iron(II)
Fe3+
ferric
iron(III)
Ag1+
silver
Silver(I)
Pb2+
plumbous
lead(II)
Pb4+
plumbic
lead(IV)

7. Polyatomic Ions Some Transition Metal naming rules:
“ic” ions have a greater (+) charge than “ous” ions
Ex. ferric (Fe3+) and ferrous (Fe2+)
Polyatomic ions—made up of two or more atoms (charge applies to the entire species)
for anions:
hypo-anion-ite < anion-ite < anion-ate < per-anion-ate in terms of O’s in the ion (all will have the same NEGATIVE charge)
Ex. ClO ClO2- ClO3- ClO4-
NOTE: not all “ate” ions will have “ite” ions

8. Writing formulas for Ionic Compounds
If you are given the name of an ionic compound, you need to follow these rules in order to write its formula:
1. Write out the formula (with charge) of the cation (first name)
2. Write out the formula (with charge) of the anion (second name)
3. The positive charges must cancel out the negative charges (criss-cross the charges)
4. The formula must show the LOWEST whole-number ratio of cations to anions.
** You CANNOT change the formula of POLYATOMIC IONS

9. Rules for Ionic Formulas
All Ionic Compounds are Neutral
This means the total Charge must be ZERO
CATIONS + ANIONS = ZERO
All Ionic Compounds start with the cation (Positive Ion) first.
All Ionic Compounds are in their lowest whole number ratio.

10. Example… Na2O Na+1 O-2 Identify the symbol for each element
Find the charge for each based on group
Criss – Cross the number without the charge
Check to make sure all rules have been followed
Sodium and Oxygen
Na O
Na O-2
Na2O

11. Example

12. More Examples Calcium and Chlorine Aluminum and Sulfur
Gallium and Phosphate

13. Nomenclature for Ionic Compounds
To name an ionic compound:
* Identify the compound as ionic (m-nm or polyatomic ion present)
* Identify the cation (first ion). Ignore how many are present.
*Identify the anion (second ion). Ignore how many are present.
* You MUST be able to recognize polyatomic ions by sight.
* Name is: cation anion
If the cation is a TRANSITION METAL you will need a roman numeral

14. The name must identify which ion it is, because transition metals have multiple Oxidation Numbers (Charges)
Name is: cation ( ) anion
*Work backwards to figure out the charge.