1. Physical Change
change in matter from one form to another WITHOUT changing what it is made of

2. Physical Change Many physical changes can be reversed.
Example: If you fold a piece of paper – this is a physical change.

3. Physical property of water
A physical property of water is that its freezing point if 0C

4. Chemical Changes
one or more substances change into new substances with DIFFERENT properties
Most of the time the change cannot be reversed
Indicators of change: bubbles of gas, odor, change in color

5. Chemical Change
If you burn paper – this is a chemical change because it cannot be reversed.
The burned piece of paper turns into ash, gases, and smoke.

6. Have you ever seen a chain that’s been left outside for a long time?
A chemical property of iron is that it combines slowly with oxygen in the air to form a different substance, RUST.
Silver reacts with sulfur in the air to form tarnish
In contrast, a chemical property of gold is that it does NOT react easily with oxygen or sulfur

7. Chemical Bonds

8. Electrons
closer to nucleus - lower energy
further from nucleus – higher energy

9. Chemical bond is an attempt to fill an electron shell.
Valence – outer shell
4 Energy Levels:
Holds just 2 electrons
Holds just 8 electrons
Maximum of 18 electrons
Maximum of 32 electrons

10. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to
N would like to
O would like to
Gain 4 electrons
Gain 3 electrons
Gain 2 electrons

11. Bonding (an attempt to fill electron shell)
Forces that hold the atoms together in compounds are called chemical bonds
The bonds form when atoms share or exchange electrons
Only those electrons having highest energies can form bonds (valence electrons)

12. Why are electrons important?
different electron configurations mean different type of bonding

13. Types of Bonds:
Ionic bonds
Covalent bonds
Hydrogen bonds
Metallic bonds

14. IONIC BOND bond formed between two ions by the transfer of electrons

16. Ionic Bonds: One Big Greedy Thief Dog!

17. COVALENT BOND bond formed by the sharing of electrons

18. 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)

19. Covalent Bonds: Unevenly matched, but willing to share.

20. Hydrogen Bonds
This type of bond is easily broken, indicating that the charges are weak.
Hydrogen bonds are responsible for several properties of water, some of which are unique

21. Hydrogen Bonds
Cohesion is the attraction between water molecules that allows them to form raindrops and to form beads on flat surfaces

22. Metallic Bond Formed between atoms of metallic elements
electrons are free to move
Good conductors of electric currents, very high melting points
Examples: Fe, Al, Au, Co

23. Metallic Bonds: Mellow dogs with plenty of bones to go around.