1. Introduction to Compounds

2. What is a compound?
A compound is a substance in which the atoms of 2 or more elements are combined in a fixed ratio
They can only be separated using chemical reactions
Represented using chemical formulas
Examples:
CO2 = carbon dioxide
C12H22O11 = sucrose (table sugar)
C3H7OH = isopropyl alcohol (rubbing alcohol)

3. The properties of the compound differ from the properties of the elements forming them because you are changing their electron structure.
Example: Forming table salt
Sodium (Na)
a very reactive metal
Chlorine (Cl)
a pale yellow poisonous gas
very reactive halogen
Sodium Chloride = NaCl
white unreactive crystal

4. Why do atoms form compounds?
Atoms form compounds to become stable.
Stable = unreactive (inert)
Electron arrangement of Noble Gases (Group 18)
Two Methods to Achieve electron stability:
Atoms can transfer valence electrons. One atom loses, another atom gains.
Ionic Compounds (salts) are formed.
Atoms can share pairs of valence electrons.
Molecular Compounds (molecules) are formed.
Valence Electrons: e- located in outermost occupied energy level of atom

5. Properties of Ionic Compounds
Usually formed by a metal w/ one or more nonmetals.
Composed of ions = charged atom
Solid, crystal room temp.
Hard and brittle
High MP due to strong crystal structure
High solubility in H20. (dissolves well)
They are electrolytes = forms ions in solution and conducts electricity when dissolved or in liquid state.

6. Crystal Structure

7. Pictures of Crystal

8. Crystal Structure of NaCl

9. Forming Ions in Solution

10. Properties of Molecular Compounds
Formed by all nonmetals.
Composed of molecules = a neutral chemically bonded group of atoms that act as a unit.
Can be a solid, liquid or room temp.; lacks crystal appearance
Low MP due to weak intermolecular forces.
Low solubility in water.
They are nonelectrolytes.

11. Model of a Molecule