2. Chemistry, Matter & Properties

3. What is Chemistry? Chemistry is the study of the properties and behavior of matter Matter is anything that has mass and takes up space A property is a characteristic that distinguishes one type of matter from another

4. All matter is made up of about 118 elements. Elements come in pieces called atoms Atoms can combine to form molecules

5. States of Matter Gas (Vapor) –No fixed volume or shape –Compressible –Molecules far apart Liquid –Fixed volume –No fixed shape –Noncompressible (practically) –Molecules closer but slide around Solid –Fixed volume and shape –Noncompressible –Molecules packed together

6. Classification of Matter Heterogeneous (beef stew) Homogeneous (solution) (salt water) Substance (chemically combined) Element (Na, K, Pb) Compound (H 2 O) Matter Mixture (physically combined)

7. Law of Constant Composition or Law of Definite Proportions A compound is always made up of the same elements in the same proportion Water is always H 2 O and is always 11% hydrogen and 89% oxygen by mass…there are other compounds containing hydrogen and oxygen, but if they don’t have these properties then they aren’t water!

8. Physical Properties Measured without changing the identity and composition of the substance. Examples –Color –Odor –Hardness –Melting/Boiling Points –Density

9. Chemical Properties Measured by reacting (changing) the substance to form a new substance Examples: –Flammability –Reaction to water or another substance

10. Extensive/Intensive Extensive – Depends on the amount of material Examples: mass and volume Intensive – Does not depend on the amount of material Examples: temperature, density, boiling point

11. Physical Changes Physical appearance may change but NOT THE COMPOSITION (it has to stay the same stuff) Changes of state (solid  liquid  gas) are physical changes

12. Chemical Changes or Chemical Reactions One substance is changed into another substance

13. Nuclear Changes a new substance is formed by changes in the atoms themselves - not just by rearranging the atoms like in chemical changes

14. Changes are either…. Endothermic – absorbing energy ex. boiling water Exothermic - releasing energy ex. Burning a candle

15. STEPS OF SCIENTIFIC METHOD 1) observation 2) hypothesis - a preliminary (before any testing) explanation based on observation the hypothesis is then tested by experimentation and 1 of 3 things happens: 1)hypothesis is totally wrong - hypothesis is thrown out 2)hypothesis is partially correct - modify hypothesis and retest 3)hypothesis passes repeated experiments

16. 3) hypothesis leads to a theory after it passes many repeated experiments Theory - explanation of why something is observed (supported by experimental evidence) Law - generalization describing the observed behavior of matter a LAW tells you what happens, a THEORY tells you why it happens.