2. –Chemical reactions occur when bonds between the outermost parts of atoms (valence electrons) are formed or broken.

3. –Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.

4. –A chemical reaction is a change in matter that produces one or more substances. -Evidence of a chemical reaction: -A gas may be produced (shown as bubbles in liquids) -A change in color -A precipitate can formIntroduction

5. Reactions that release heat.

6. Reactions that absorb heat.

7. Chemical Reactions on a Small Scale In chemical reactions, changes involve the rearrangement of atoms. The force that holds atoms together is called chemical bond. Individual atoms are bonded to other atoms in molecules Molecule- a particle made of two or more atoms bonded together.

8. Elements Forming Compounds Compound- a substance made of two or more elements that have been chemically combined. Water, carbon dioxide, table salt, and baking soda are familiar compounds.

9. Chemical vs. Physical Reactions Chemical: –One or more substances are formed Ex. –Rusting Metal –Burning Candle –Milk Spoiling Physical: –Object may change its state of matter but will still contain the same particles as the starting substance Ex. –Water Boiling –Ice Melting

10. –Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction