1. Dalton described the atomic nature of matter – is that the end of the story?

2. Objectives
To learn more about how the understanding of atomic structure developed
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

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

4. A. The Structure of the Atom
The Plum Pudding (Chocolate Chip Cookie) Model
The Discovery of the Electron

5. A. The Structure of the Atom
Rutherford’s Experiment (1911)
α particles are very small and positively charged

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

9. Large Hadron Collider
video
Circular tunnel 27km in circumference near Geneva
Protons or lead nucleii smashed into targets
$4 billion cost – limited operation to date

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

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

12. 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. 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
WOC page 88 - Q 29, 30