1. Unit 2: Atomic Theory and Structure

2. (c. 400 B.C.) Democritus proposed that “atomos” are indivisible. Atom: smallest particle of matter that retains its properties. Early Models of the Atom (1803) Dalton’s experiments developed a scientific theory of atoms. Dalton’s Atomic Theory (4 conclusions)

3. 1)All matter is composed of tiny, indivisible atoms. Dalton’s Atomic Theory 2)In size, mass, & prop’s atoms of the same element are identical, atoms of different element are different

4. 4)Atoms combine in simple whole-number ratios to form compounds. 3)Atoms chemically combine, separate, or rearrange. (Law of Definite Proportions) (Law of Conservation of Mass) Dalton’s Atomic Theory

5. Cathode Ray Tube (1904) J.J. Thomson Cathode Ray Tube Experiment

6.  cathode rays deflect toward a positive plate (1904) J.J. Thomson Cathode Ray Tube Experiment WHY? negatively charged

7. Conclusion:  atoms contain negatively charged particles called electrons Thomson’s Plum Pudding Model atoms are + charged material with – charged electrons evenly distributed (1904) J.J. Thomson Cathode Ray Tube Experiment

8. 1908 Nobel Prize for work with radiation (+ alpha particles) (1911) Ernest Rutherford Gold Foil Experiment (expected)

9. 1/10,000 + alpha particles deflect from the gold foil (1911) Ernest Rutherford Gold Foil Experiment +

10. Conclusion:  atoms are mostly empty space filled with e –  the + charge and mass are in a tiny central nucleus nucleus: tiny, massive, core of atoms containing + protons and (neutral) neutrons (1911) Ernest Rutherford Gold Foil Experiment

11. (1 trillionth of the atom) the atomic nucleus

12. 17.7 The Atomic Nucleus 3 subatomic particles: ≈ 0≈ 0

13. 4.2

14. 1. The ancient Greek philosopher Democritus is credited with suggesting that ____. A.atoms react in whole number ratios B.atoms can change into other elements C.all matter is made of indivisible atoms D.atoms are stupid anyway Quick Quiz!

15. 2. Dalton's atomic theory improved earlier ideas about atoms by ___. A.teaching that all matter is composed of tiny particles called atoms B.theorizing that all atoms of the same element are identical C.using experimental methods to establish a scientific theory D.not relating atoms to chemical change Quick Quiz.

16. 3. Which of the following is NOT part of Dalton’s atomic theory? A.All elements are made of atoms. B.Atoms of the same element are identical. C.Different elements can mix or combine in simple whole-number ratios called compounds. D.Atoms can be changed into other atoms through chemical reactions. Quick Quiz.

17. 4. Which of the following is TRUE about subatomic particles? A.protons and neutrons are positively charged B.electrons have practically no mass C.protons and electrons are in the nucleus D.neutrons and electrons have no charge Quick Quiz.

18. 5. Most of the volume of the atom is occupied by the ________________. A.electrons B.protons C.neutrons D.protons and neutrons