1. Science 9
Chapter 3

2. Compounds
A pure substance made of two or more kinds of elements combined in fixed proportions.
Represented by a chemical formula.
Chemical bonds hold them together.
Are either ionic or covalent.

3. Covalent Compounds
Atoms combine by sharing electrons to form molecules.
Molecules: a group of atoms held together by sharing one or more pairs of electrons.
Examples include carbon dioxide and water.
Formed from non-metals only.
They do not conduct electricity.
May be a solid, liquid, or gas at room temperature

4. Methane, CH4

5. Examples of Common Covalent Compounds
Table sugar C12H22O11
Carbon Dioxide CO2
Water H2O
Methane CH4

6. Ionic Compounds Atoms gain or lose electrons to form ions.
All the positive ions attract all the negative ions everywhere in the same crystal.
Formed from metals and non-metals.
All are solid at room temperature.
High melting and boiling points.
Will conduct electricity when melted or dissolved in water.
Are also called “salts”.

7. Cation – an atom that has lost electrons to become positively charge.
Anion – an atom that has gained electrons to become negatively charged.
Always formed by non-metals
Cation – an atom that has lost electrons to become positively charge.
Always formed by metals
Therefore in ionic compounds, anions and cations are attracted to each other and bond to from the compounds by the cation transferring electrons to the anion.

8. Examples of Common Ionic Compounds
NaCl Sodium Chloride
CaCO3 Calcium Carbonate
Na2SO4 Sodium Sulfite
NaOH Sodium Hydroxide

9. Naming Compounds Every compound has a...
Name: indicates the elements present in the compound (ionic only! In covalent compounds the name also indicates the ratio of each element present)
Formula: indicates the symbols and ratio of each element present in the compound.

10. Rules for Naming Ionic Compounds
Name the metal
Name the non-metal using the root word and add the ending “ide”
Ex. MgBr2
Magnesium bromide
Ex. Li3N
Lithium nitride

11. Practice Problems
Page 82

12. Rules for Naming Covalent Compounds
Prefixes
Name the first atom
Name the second atom using the root word and add the ending “ide”
Add prefixes to the atom names to indicate the number of each atom in the compound
Exception to the rule: If the first element has only one atom, you do not need to add the prefix “mono”
1 – mono 2- di 3 – tri 4 – tetra 5 – penta 6 – hexa 7 – hepta 8 – octa 9 – nona 10 - deca

13. Ex: CO
Carbon monoxide
Ex: SiCl4
Silicon tetrachloride

14. Practice Problems
Page 83

15. Physical and Chemical Changes

16. Physical Changes
the appearance of a substance may have changes but the bonds holding the atoms together in molecules and ions have not been broken and no new bonds have been made.
Includes:
all changes in state (melting, evaporation, condensation, freezing)
Dissolving
Cutting
Tend to be easy to reverse.

18. Chemical Changes
Produce new substances with new properties; may or may not be noticeable.
New bonds are formed while others are broken.
Chemical equations can be written for all chemical changes.
For example the composition of water.
2 H O2  2 H2O
Reactants Products

19. In a chemical reaction the mass of the reactants = the mass of the products. The elements are conserved but not the compounds.
Ex. Corrosion, fruit ripening, combustion

20. Evidence of a Chemical Change
1. Color change
2. Heat, light, sound produced or consumed
3. Gas bubbles released
4. A precipitate formed
5. Difficult to reverse

22. Applications of Chemical Changes
Harnessing combustion
Combustion releases large amounts of energy which can be used to provide heat and light, electrical and mechanical energy.
Solving the corrosion problem (a process by which metals combine with oxygen; oxidation)
Using chemical change for traditional products (example: tanning hides, making dyes and medicines from plants, and preserving food)

23. Core Lab Activity 3-3C pg. 92-3
Observing Changes in Matter

24. :“Plastics and Modern Life”
CORE STSE
:“Plastics and Modern Life”