Formulas of Binary Ionic Compounds
• Composed fron only two elements: one metal
and a nonmetal (NaCl, CaF2, FeCl3)
• Group IA : +1 charge
• Group IIA: +2 charge
• Group IIIA: only Al 3+ charge
• Group VIIA: -1 charge
• Group VIA: -2 charge
• Group VA: only N and P -3 charge.
Rule for writing binary ionic
compounds
• Cation always comes before the symbol of the
anion.
• Sum of the positive charges on the cation
must equal the sum of the negative charges
on the anions so that the formula of the
compound is electrically neutral.
• Whole numbers, writes as subscripts indicate
the number of each ion in the formula unit.
• The smallest set of numbers must be used.
Example:
• Fe3+ & Cl• Fe 3+
=3+
• Cl-Cl-Cl- = 3--------------------FeCl3
= 0 net charge
Another way
• Use the size of the charges on the two ions to
get the subscript numbers for the formula:
Example Problems:
• Use the two ions to write a correct formula for
an ionic compound
• Mg2+ O2• Na+ N3• Hg22+ Cl-
Naming Binary Compounds
• Using systemic names:
• Single-cation metals: main group metals. Name of
the cation followed by the name of the anion
– Eg: Li+ : lithium ion, Ca2+: Calcium ion, Al3+: aluminum
ion
Rules:
Name of the cation comes first
Cation is the name of the metal
the name of the anion ends in –ide
KBr: potassium bromide, Al2O3: aluminum oxide,
Na2S: sodium sulfide
Example Problems
•
•
•
•
Correctly name these ionic compounds:
LiCl & CaCl2
Mg3N2 & Na3N
AlP & AgCl
Naming Compounds w/ Multiple
Cation Metals
• Mostly used with transition metals because
they are able to form two or more ions.
• Uses the Stock System: name of the metal
with its charge written as a Roman numeral.
• Classical system: not common anymore, uses
the –ous, -ic ending on the name of the metal
to indicate the lower and higher charge.
Stock Name v. Classical Name
•
•
•
•
•
•
•
Copper Ion
Copper (II) ion
Mercury (I) ion
Mercury (II) ion
Chromium (II) ion
Chromium (III) ion
•
•
•
•
•
•
Cuprous ion
Cupric ion
Mercurous ion
Mercuric ion
Chromous ion
Chromic ion
Example Problems
• Use the Stock method to name these ionic
compounds involving multiple-cation metals
• FeO & Fe2O3
• CrCl3 & Hg2Cl2
Chemical Formula
Indicates the relative # of atoms of each
kind in a molecular compound (covalent
bond = single molecule) and in an ionic
compound (ionic bond= one formula unit)
CH4 (methane)
NaCl (salt)
How many atoms are in each compound?
Pb(NO3)4 (lead (IV) nitrate)
Naming Monatomic Ions
Cations  Elements name + cation
Al3+
is?
Anions  Drop ending of elements name,
add –ide + anion
Cl-
is?
Binary Ionic Compounds
Compounds composed of 2 elements
where the total number of + and –
charges must be = (**in the smallest
possible whole ratio though)
Stock System of
Nomenclature
Using a roman numeral to indicate an
ion’s charge when there is more than
one possible charge (cations)
No element forms more than one
monatomic anion
How do you know the charge from a
compound? Lithium is??
1 way is…
Li2O
Polyatomic Ion Compounds
Oxyanions: polyatomic ions that
contain oxygen (usually can form
more than 1 type)
2 types  -ite smaller # -ate larger #
3-4 types  hypo- plus -ite (smallest), -ite,
-ate, per- plus -ate (largest)
Sulfate
Ion
Naming Binary
Molecular Compounds
2 systems used:
1. Old System = Prefix system of nomenclature
(see Page 269 for prefixes – memorize these)
PF5
Phosphorus pentaflouride
2. New System = Stock system (using
oxidation numbers)
Oxidation Numbers
NOT ACTUAL physical
characteristics of atoms
The number of electrons that must
be added or removed from an
atom in a combined state to
convert the atom into the
elemental form
Stock System vs Prefix System
Prefix System
Carbon dioxide
Prefix System
Carbon tetrachloride
Prefix System
Phosphorus pentachloride
Prefix System
Selenium hexafluoride
Prefix System
Arsenic pentaoxide
Assigning Oxidation
Numbers
SEE HANDOUT!!
Let’s try some together……
Common Binary Acids
Acids that consist of two elements
Usually hydrogen + halogen
Oxyacids = Hydrogen ,oxygen, and a
third element (nonmetal)
MEMORIZE = Hydrochloric acid,
Phosphoric acid, Nitric acid,
Sulfuric acid, Acetic acid, Carbonic
acid (Pg 272 in textbook)
Law of Conservation of Mass
In all reactions, chemical or
physical, mass is
neither created nor
destroyed
Chemical reactions: Mass
of products always
equals mass of reactants
Law of Definite Proportions
The fact that a chemical compound
contains the same elements in exactly
the same proportions by mass
regardless of the size of the sample or
source of the compound
Water is always: 11.2% H and 88.8% O
Law of Multiple Proportions
When elements combine, they do so in
the ratio of small whole numbers
For example carbon and oxygen react to
form CO or CO2, but not CO1.8
1.00 g C + 1.33 g O = CO
1.00 g C + 2.66 g O = CO2
PRACTICE TIME!!
Chemical Quantities
Formula Masses
“Average mass”  sum of the average
atomic masses of all atoms
represented in its formula, whether it
be a formula unit, molecule, or ion
CO2
C = 12.01 x 1 = 12.01 amu
O = 16.00 x 2 = 32.00 amu
44.01 amu
Let’s try some……..
Molar Masses
Molar mass = g/mol
Grams come from mass # on the periodic
table
Grams # = 1 mol of the atom
So the molar mass of Chlorine is 35.45 g/mol
Calculated like formula mass because…
Formula mass (amu) = Molar mass (g/mol)
Molar Mass Conversion Factor
Grams
Moles
Moles
Grams
Moles
Molecules
Grams = mass
Moles = amount
Molecules = number of atoms
Volume at STP
Molar volume: The volume occupied
by 1 mole of a gas at standard
temperature and pressure
1 mol = 22.4 L (at STP)
Percentage Composition
Mass of element x 100 = % of element in
Mass of compound
compound
Find element grams based on # of moles
of each element in the compound.
Find molar mass by addition of elemental
gram results.
“Plug” in the #’s to the formula…YAY!
Calculation of
Empirical Formulas
Smallest atomic ratio possible
Change % (composition) to grams (mass
composition)
Convert g to moles using molar mass
conversion factor
Find ratio of smallest whole #’s by dividing
each # of moles by smallest # of moles you
have
Round decimals in ratios to nearest whole #
Time to Practice Again
Calculation of
Molecular Formulas
Actual formula of molecular compound
x(empirical formula {mass}) =
molecular formula {mass}
Therefore x = molecular formula mass
empirical formula mass