1. Go to section Chapter 4 Atomic Structure

2. Go to section History of Atom Democritus (2500 YEARS AGO) Greek philosopher –Atmos – “uncut” or “indivisible” Dalton (1800’s) British Scientist –Proposed the first Atomic Theory All elements are composed of atoms All atoms of the same element are the same Compounds contain atoms of more than one element In a compound, atoms combine in the same way

3. Go to section History of Atom

4. Go to section History of Atom J.J. Thompson (early 1900’s) –Cathode Ray Tube Experiment –Discovered the first sub-atomic particle, the electron A particle smaller than the atom Has a negative charge –Change: Proposed the “plum pudding” model Milikan did the oil-drop experiment –Determined the charge of the electron

5. Go to section Thomson’s Experiments Figure 5 Cathode Ray Tube Experiment

6. Go to section History of Atom Rutherford (1900’s) –Gold-foil experiment Alpha particles shot at a thin gold foil Particles were expected to go right through Some were deflected and even bounced back Conclusion – there was a nucleus in the middle where the + charge is found Model changed again

7. Go to section The Gold Foil Experiment Figure 5

8. Go to section History of the Atom From Dalton to Rutherford

9. Go to section A Scientific Method Figure 12

10. Go to section Structure of Atom Atomic number: the number of protons found in the nucleus –Unique to each element –A whole number (count the # of protons) –Will be found on the periodic chart Mass number: the number of protons AND neutrons in the nucleus. –This will change because it can gain or lose neutrons # of neutrons = Mass # - atomic #

11. Go to section a.16 – 8 = 8 b.32 – 16 = 16 c.108 – 47 = 61 d.80 – 35 = 45 e.207 – 82 = 125

12. Go to section Structure of Atom Isotopes: Will have the same atomic number ( # of P+) But different mass number –This is because there will be more or less neutrons –Isotopes are still neutral because the neutrons are neutral Atomic mass it the average mass of the commonly occurring isotopes.

13. Go to section History of Atom Bohr’s Model (1900’s) He focused on the electrons –Found that they had certain energy levels –Proposed that the have fixed, specific orbits Change: Orbit model Evidence for this – gaining and releasing of energy from an atom

14. Go to section History of Atom Schrodinger – mathematician (1900’s) Electron Cloud Model –Found that they had certain energy levels –Instead of fixed, specific orbits, there are orbitals Orbital is a proposed area where the electron is likely to be found Change: Electron cloud model

15. Go to section History of Atom Modern Theories: Bohr Model to Electron Cloud Model

16. Go to section Structure of Atom quantum mechanical modelIn the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high.

17. Go to section The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.

18. Go to section Reading Strategy a.Electron moves to higher energy level. b.Electron moves to lower energy level. Section 4.3 Sequencing

19. Go to section Number of Orbitals and Electrons in Energy Levels Figure 15

20. Go to section Structure of Atom Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell- shaped. These are probable locations where an electron is most likely to be found.

21. Go to section Structure of Atom Four of the five d orbitals have the same shape but different orientations in space.

22. Go to section Reading Strategy Summarizing Section 4.1 a.Daltonb.Indivisible, solid spheres c. Thomsond. Negative charges evenly scattered through a positively charged mass of matter (plum pudding model) e.Deflection of alpha particles passing through gold foil