IONIC COMPOUNDS
Ionic Compounds:

Form when metals and nonmetals combine
by transferring electrons
 Metal atoms lose electrons to form positive
ions
 Nonmetal atoms gain electrons to form
negative ions
 Electrons are transferred from metal to
nonmetal, and the resulting charged
particles (ions) form an IONIC BOND
Ionic Charges

Determined by the number of electrons in
the outermost “shell” – VALENCE
 Eg. Aluminum: Al has 13 protons, 13
electrons (2 in first shell, 8 in second, 3 in
third)
 Al will lose the 3 electrons in the outermost
shell and therefore has a valence of 3
Formulas for Ionic
Compounds:

Eg. Calcium iodide
 Write the symbols for elements: Ca I
 Write the ionic charges: Ca 2+
I 1 Select the number of ions to balance the
charge CaI2
Criss-Cross Rule
Calcium Iodide
2+
1-
Ca
I
Nickel and Oxygen

Write chemical symbols: Ni
O
 Determine valence or ionic charges Ni2+
O 2
Use criss cross rule:
2+
2-
Ni
O

Write formula: Ni2O2

Reduce formula: NiO
POLYATOMIC COMPOUNDS

Pure substances involving combinations of
metals and polyatomic ions
 POLYATOMIC IONS are groups of atoms
that tend to stay together and carry an
overall ionic charge
 Eg. Nitrate NO3 Eg. Sulfate SO42-
Formulas for polyatomic
compounds:





Eg. What is the formula for the ionic compound
formed by sodium and a hydroxide ion?
WRITE THE SYMBOLS FOR THE IONS:
Na
OH
WRITE THE CHARGES ABOVE EACH:
1+
1Na
OH
CRISS CROSS CHARGES AND SYMBOLS
WRITE THE FORMULA: NaOH
Naming polyatomic
compounds:

Combination of the metal and the name of
the polyatomic ion

Eg. NaOH
sodium hydroxide
Determine the formula and
name the compound formed
by combining calcium and
carbonate ion.
2+
Ca
2-
CO3
-
CaCO3
Calcium carbonate
MOLECULAR COMPOUNDS

Most of the compounds you encounter
everyday do not contain ions. Instead they
contain molecules which share electrons to
form stable arrangements.
 This sharing of electrons is called a
covalent bond.
 Many nonmetals form covalent bonds.
Diatomic Molecules

Certain elements such as oxygen exist as
covelently bonded molecules.
 The table on p. 202 of your text lists the
elements that form diatomic molecules.
Copy the information into your notes.
Prefixes in Molecular Compounds
Prefix
mon(o)ditritetrapent(a)-
Number
1
2
3
4
5
Example
CO
CS2
SO3
CF4
PBr5
Formulas for molecular compounds:
•
E.g. What is the formula for a compound formed between
carbon and sulfur?
• Write the symbols and their combining capacities. Write the one
with the larger combining capacity first:
4
2
C
S
• Criss cross combining capacities to produce subscripts:
C2S4
•
Reduce the subscripts if possible:
CS2
Naming Molecular Compounds:




Molecular compounds containing hydrogen are named
as if they were ionic compounds.
eg. H2S hydrogen sulfide
Others have common names such as water (H2O),
ammonia (NH3), or methane (CH4).
In general, prefixes are used to count the number of
atoms when the same two elements form different
combinations.
IF there is only one atom of the first element, the
prefix “mono” is not used.
eg. CO Carbon monoxide
eg. CO2 Carbon dioxide