1. Grade 9 Science: Unit 1: Atoms, Elements, and Compounds
Chapter 3: Elements combine to form compounds

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. Model of HCl ( hydrochloric acid)

4. 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.

5. Formed from non-metals only.
They do not conduct electricity.
May be a solid, liquid, or gas at room temperature.

6. Methane CH4

7. H C H C H H H

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

9. 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.

10. All are solid at room temperature.
High melting and boiling points.
Will conduct electricity when melted or dissolved in water.
Are also called “salts”.

11. Magnesium Chloride MgCl2

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

13. Naming Compounds
Every compound has a...
Name: indicates the elements present in the compound
Formula: indicates the symbols and ratio of each element present in the compound.

14. Rules for Naming Compounds
Ionic Compounds
See page 81-2
Covalent Compounds
See page 83
Complete practice problems on
pages 82 &83

15. Physical & Chemical Changes
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.

16. Tend to be easy to reverse.
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.

19. Chemical equations can be written for all chemical changes.
For example the composition of water.

20. 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

21. Evidence of a Chemical Change:
Color change
Heat, light, sound produced or consumed
Gas bubbles released
A precipitate formed
Difficult to reverse

23. 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.

24. 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)

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

26. CORE STSE: “Plastics and Modern Life”