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

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

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

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

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.

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

Chemical Bonds

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

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

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

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)

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

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

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

Ionic Bonds: One Big Greedy Thief Dog!

COVALENT BOND bond formed by the sharing of electrons

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

Covalent Bonds: Unevenly matched, but willing to share.

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

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

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

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