1. MAIN IDEAS 1.Atom 2.Dalton’s Atomic Theory KEY CONCEPTS 1.How did Democritus describe atoms? 2.How did John Dalton further Democritus’s ideas on atoms 3.What instruments are used to observe individual atoms? IaN pg. 3

2. A.Democritus (460-370 B.C.) 1. Atoms indivisible & indestructible 2. Couldn’t explain chemical behavior 3. No experimental evidence! 4. Atomos (Greek) = indivisible I. Theories about the Atom

3. B. John Dalton (1766 - 1844) 1. English Chemist & School Teacher 2. Experimentation supports Democritus’ theories a. Ratios of elements in reactions

4. a. All elements are composed of tiny indivisible particles called atoms. b. Atoms of the same element are identical. The atoms of any one element are different from those of another element. c.Atoms of different elements can physically mix together or can chemically combine in simple whole # ratios to form compounds. d.Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element however are never changed into atoms of another element as a result of a chemical reaction 3. DALTON’S ATOMIC THEORY

5. II. Sizing up the Atom A. Radii range of atoms 5 X 10 -11 m to 2 X 10 -10 m B. Scanning Tunneling Microscope = observable individual atoms!