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 SO 3 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 3.1 Empirical 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 Chemical Formula Class (I or m) State (s, l, g) Solubility (yes/no) Solution color Electrical conductivity (yes/no)

Evidence Table – Inv. 3.1 Chemical formulaClassStateSolubilitySolution 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 ChemicalFormulaClassStateElectrical 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) C 3 H 4 OH(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 Acids are solid, liquid or gas as pure compounds at SATP aqueous solutions conduct electricity makes blue litmus paper turn red Bases contains hydroxide “OH” makes red litmus paper turn blue