Ionic and Molecular Compounds

Classifying Compounds

There are about 109 elements but they can be combined to make millions of compounds.

Elements are commonly classified as METALS and NONMETALS, therefore compounds are formed three combinations:

1. metals-nonmetals: ionic compounds NaCl

2. nonmetal-nonmetal: molecular compounds

SO3

3. metal-metal: inter-molecular compounds

Brass (CuZn) an alloy

Method for Classification

The properties of compounds can be used to classify compounds as ionic or molecular.

Diagnostic Tests- a lab procedure conducted to identify or classify chemicals.

Important states of matter in chemical formulas: solid (s), liquid (l), gas (g), and aqueous (aq).

Investigation 3.1Empirical Definitions of Compounds

Based on you experience, what properties might be used to classify compounds as ionic or molecular?

Why is a control conductivity test on tap water?

Disposal – all chemical waste can be disposed down the drain with lots of water.

Evidence Table

ChemicalFormulaClass (I or m)State (s, l, g)Solubility (yes/no)Solution colorElectrical conductivity (yes/no)

Evidence Table – Inv. 3.1

Chemical formula Class State Solubility Solution

Color

Electrical

Conductiv

Analysis

Empirical definitions – what properties are true for ionic and molecular

Evaluation

What is judged to be adequate: design, procedure, and skills?

Are you confident in your results?Where your prediction correct?What can you do to improve your

confidence in these definitions?

Empirical or Theoretical Information?

Both empirical and theoretical information is used to form the above definitions. Can you pick out what information is empirical on the previous slide?

Definitions of Ionic and Molecular Compounds

Ionic Compounds all solid at SATP aqueous solutions conduct electricity transfer of electrons when forming bonds metal-nonmetal

Molecular Compounds solid, liquid and gases at SATP aqueous solutions do not conduct electricity share electrons when forming bonds nonmetal-nonmetal

Lab Exercise

In science, it is not uncommon for new evidence to conflict with widely known and accepted theories. This does not create a problem but an opportunity to improve understanding

Lets test some more compounds and see if the properties turn out as we would predict

Investigation

Lets test some more compounds to support our empirical definitions for ionic and molecular compounds

Evidence Table must include:

Chemical name Formula class State Electrical conductivity

Evidence Table

Chemical Formula Class State Electrical Conductiv

Analysis Do the properties of the compounds match the

predictions?

Evaluation What is judged to be adequate: design, procedure,

and skills? Are you confident in your results? Where your predictions correct? What to do if something does not fit…restrict, revise

or replace?

Restrict, Revise or Replace

Problem – hydrogen citrate (citric acid)C3H4OH(COOH)3

This is made up of nonmetals so you would predict a molecular compound but it conducts electricity, and may be ionic.

We need to a revision…

A third class of compounds called ACIDS.

Acids and Bases

Acidsare solid, liquid or gas as pure compounds

at SATPaqueous solutions conduct electricitymakes blue litmus paper turn red

Basescontains hydroxide “OH” makes red litmus paper turn blue