Classification of Compounds
Classifying Pure Substances
• Last class: Classification of elements into
metals nonmetals metalloids
• This class: Classification of Compounds
Three classes of Compounds
1) Metal-nonmetal: Ionic compounds
2) Nonmetal-nonmetal: Molecular compounds
AKA Covalent compounds
3) Metal-metal: Alloys
Example of Alloys:
Brass = Cu5Zn8
Empirical Classification of Ionic and
Molecular Compounds
Identifying ionic compounds and molecular
compounds:
- divided by their properties.
- leads to an empirical definitions of both
groups
Diagnostic Tests: A lab procedure. Using easy to
obtain properties that are different between
inorganic and molecular (organic) compounds
to identify compounds.
Examples of Diagnostic Tests
- Using acid base indicators
- Cobalt chloride paper changes from blue to
pink if it comes in contact with water.
- Hydrogen makes a popping sound when it
comes into contact with a flame
- Oxygen gas will relight a snuffed out match
Empirical Definitions of Compounds
Empirical Definition: List of empirical properties
that define a class of chemicals
Ionic Compounds:
- Solid at standard atmospheric temperature
and pressure (SATP).
- When dissolved in water they conduct
electricity
Empirical Definitions of Compounds
Molecular Compounds:
- Solid, liquid or gas at standard atmospheric
temperature and pressure (SATP).
- When dissolved in water they do not conduct
electricity
Empirical Definition of Acids
Acids are a group of compounds that have
characteristics of more than one class
Characteristics of…
Organic (molecular) compounds: Acids are
composed of nonmetal elements.
Ionic compounds: Acids conduct electricity
Empirical Definition of Acids
Acids:
-Solids, liquids or gases (at SATP)
-Conduct electricity when dissolved in water
-Turns blue litmus paper red
Empirical Definition of Bases
Bases: Turns red litmus paper blue.
Neutral Compounds: Do not change the color of
either red or blue litmus paper.
Binary Ionic Compounds
The first class of ionic compounds
- Binary ionic compounds: Made of 2 kinds of
atoms (2 kinds of monatomic ions)
Eg. NaCl
Made from Na cation (Positively charged ion)
and a Cl anion (Negatively charged ion)
Ionic Compounds
Empirical Formula of Ionic Compounds:
Made by measurements taken
1) by combining elements into compounds
2) by chemically decomposing compounds into
elements
Balancing Charges
How do we explain the empirically determined ionic
formula for compounds?
1) Predict the charges on an ion based on atomic
theory
2) Balance the charges of the ions that you are
combining by multiplying
Eg. Al = 3+Cl = 1Al = 3+
3 xCl = 3Tells you that 3 Cl ions are needed in the formula
AlCl3
Explaining Polyatomic ions
Not all ions were monatomic = New class of
ionic compounds  Polyatomic ions (Poly =
more than 1)
Use the same steps as binary ionic compounds
to find chemical formula
Explaining Multivalent Ions
Multivalent ions: Valent = valence shell or outer
most ion shell Multi = more than one
Result: They have more than one possible
number of electrons on their outer shell
Eg. Cu 2+ Versus Cu 3+
Cu 2+ = Has 2 electrons on the outer shell
Cu 3+ = Has 3 electrons on the outer shell
Hydrates
Hydrates: Decompose at low temperatures to
produce water along with another compound.
The water acts like part of the compound not as a
solvent
Eg. Bluestone: CuSO4. 5H2O = Blue crystal
Heat to evaporate water = CuSO4 = White powder
Summary Table mixes to hydrates