Understanding Atomic Structure & Isotopes

1. Objectives • To learn about the internal parts of an atom • To understand Rutherford’s experiment • To describe some important features of subatomic particles • To learn about the terms isotope, atomic number, and mass number • To understand the use of the symbol to describe a given atom

2. A. The Structure of the Atom Democritus - atomos Lavoisier Law of Conservation of Mass Dalton Atomic Theory Proust Law of Constant Composition

3. A. Atomic Structure Dalton – viewed atoms as hard round objects • Dalton’s theory led to two questions • What accounts for the differences in properties between atoms of different elements? (Why do atoms of one element behave differently than atoms of another element?) • What forces hold atoms together in compounds?

4. A. The Structure of the Atom • Experiments by J.J. Thomson showed that atoms contain electrons. • Cathode ray tube

5. A. The Structure of the Atom The Plum Pudding Model

6. A. The Structure of the Atom Rutherford’s Experiment

7. 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

8. 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.

9. B. Introduction to the Modern Concept of Atomic Structure Comparing the Parts of an Atom

10. C. Isotopes • Isotopes are atoms with the same number of protons but different numbers of neutrons.

11. C. Isotopes • A particular isotope is represented by the symbol .