When two or more substances react to produce new compounds with different physical and chemical properties.

Molecules -- Substances composed of 2 or more atoms. Examples: O 3 -- Ozone Gas 3 atoms H 2 -- Hydrogen Gas 2 atoms H 2 SO 4 -- Sulfuric Acid 7 atoms HCl -- Hydrochloric Acid 2 atoms

Compounds – a pure substance composed of 2 or more different elements that are chemically combined. The elements are held together with chemical bonds. Examples: H 2 0 Water 2 Hydrogen and 1 Oxygen CO 2 Carbon Dioxide 1 Carbon, 2 Oxygen. C 2 H 6 O 2 Sugar 2 Carbons, 6 Hydrogens, 2 Oxygens

Reactants - the substances that you start with before the reaction. – the ingredients Products – the substances that are made from the chemical reaction ENERGY CAN BE A REACTANT OR A PRODUCT TOO!!!ENERGY CAN BE A REACTANT OR A PRODUCT TOO!!! Parts of a chemical reaction:

How do you know if a chemical reaction is happening? Bubbling - gas is being made Odor or smell not there before Color change in any of the substances New phase or state appears Size or shape change in materials Heat / light / sound / Electric energy is produced

Types of Chemical Reactions. Exothermic Reaction productExothermic Reaction – a reaction that has HEAT energy as a product – It is released out during the reaction Ex: Burning wood, Mg and HCl, Sodium and water, fireworks. Endothermic Reaction reactantEndothermic Reaction – a reaction that has HEAT energy as a reactant – It is absorbed in from the surrounding objects or materials. Ex: Medical cold packs

Chemical Formula A short-hand method of showing the composition of a compound or other substance. H 2 SO 4 Mg(OH) 2 Subscript Subscript – multiple number of the element it follows Polyatomic Ion Polyatomic Ion – a group of elements acting as one ‘atom’ It is shown using ( ).

Chemical Bonds Atoms form bonds when going through chemical reactions. These bonds hold the atoms together to form compounds. IonIon – an atom with a (+) or (-) charge that is formed through chemical reactions. Two types of bonds: Ionic Bond: occurs between metals – nonmetals Covalent Bond: occurs between nonmetals.

Ionic Bond Ionic Bond: occurs between metals & nonmetals. Metals give away their valence electrons causing them to become (+) charged ions. They give all of them away until the ring is empty. Nonmetals take the valence e- from the metal and they become (-) charged ions. They will take e- until they have 8e- on their last shell. Opposite charged particle attract to each other. So the (+) ions attract to the (-) ions. All atoms want to have a full outer shell with 8 valence electrons.