1. Section 3.3 Atomic Structure Dalton described the atomic nature of matter – is that the end of the story?

2. Section 3.3 Atomic Structure JOHN DALTON Thought that atoms were solid spheres- kinda like a billiard (pool) ball. This theory had to later be revised. WHY?

3. Section 3.3 Atomic Structure A. The Structure of the Atom Experiments by J.J. Thomson in the 1890’s showed that atoms contain electrons. Cathode ray tube Electric Potential = Voltage The Discovery of the Electron

4. Section 3.3 Atomic Structure A. The Structure of the Atom by JJ Thomson The Plum Pudding (Chocolate Chip Cookie) Model The Discovery of the Electron

5. Section 3.3 Atomic Structure A. The Gold Foil Experiment Ernest Rutherford’s Experiment (1911) He discovered the positively charged nucleus

6. Section 3.3 Atomic Structure A. The Structure of the Atom Results of the Rutherford experiment (a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct (b) Actual results

7. Section 3.3 Atomic Structure B. Introduction to the Modern Concept of Atomic Structure Ernest Rutherford showed that atoms have internal structure. –The nucleus, which is at the center of the atom, contains protons (positively charged) and neutrons (uncharged). –Electrons move around the nucleus. The Discovery of the Atomic Nucleus

8. Section 3.3 Atomic Structure B. Introduction to the Modern Concept of Atomic Structure Comparing the Parts of an Atom

9. Section 3.3 Atomic Structure Determining the number of subatomic particles Protons are equal to the atomic number above the symbol on the periodic table. Electrons are equal to the number of protons only in NEUTRAL atoms. Neutral atoms have no charge so the positively charged protons must cancel the negatively charge electrons Neutrons: subtract the number of protons from the mass number

10. Section 3.3 Atomic Structure C. Isotopes Isotopes are atoms with the same number of protons but different numbers of neutrons.

11. Section 3.3 Atomic Structure C. Isotopes A particular isotope is represented by the symbol. e.g. Carbon: What is Z for 12 C, 13 C and 14 C?

12. Section 3.3 Atomic Structure Isotopes True or False? Atoms that have the same number of neutrons but different number of protons are called isotopes True or False? The mass number of a nucleus represents the number of protons in the nucleus Are all atoms of the same element identical? If not, how do they differ? Is this consistent with Dalton’s atomic theory?

13. Section 3.3 Atomic Structure Isotope Math What is the symbol for the isotopes below?  Z = 8, number of neutrons = 9  Isotope of chlorine with A = 37  Z = 27, A = 60  Number of protons = 26, number of neutrons = 31  The isotope of iodine with a mass number of 131  Z = 3, number of neutrons = 4