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

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

                                       

–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 form

IntroductionIntroduction

Reactions that release heat.

Reactions that absorb heat.

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.

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.

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

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