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 compounds2) Nonmetal-nonmetal: Molecular compounds

AKA Covalent compounds3) 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 groupsDiagnostic 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. NaClMade from Na cation (Positively charged ion)

and a Cl anion (Negatively charged ion)

Ionic Compounds

Empirical Formula of Ionic Compounds:

Made by measurements taken1) 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 theory2) Balance the charges of the ions that you are

combining by multiplying Eg. Al = 3+Cl = 1-Al = 3+ 3 xCl = 3-Tells 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

HydratesHydrates: 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