Section 3.3

Atomic Structure

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

Section 3.3

Atomic Structure

Objectives

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

2. To learn about the internal parts of an atom

3. To understand Rutherford’s experiment

4. To describe some important features of subatomic particles

5. To learn about the terms isotope, atomic number, and mass number

6. To understand the use of the symbol to describe a given atom

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

Section 3.3

Atomic Structure

A. The Structure of the Atom

The Plum Pudding (Chocolate Chip Cookie) Model

The Discovery of the Electron

Section 3.3

Atomic Structure

A. The Structure of the Atom

Rutherford’s Experiment (1911)

α particles are very small and positively charged

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 theplum pudding model had been correct

(b) Actual results

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

Section 3.3

Atomic Structure

B. Introduction to the Modern Concept of Atomic Structure

Comparing the Parts of an Atom

Section 3.3

Atomic Structure

Circular tunnel 27km in circumference near Geneva

Protons or lead nucleii smashed into targets

$4 billion cost – limited operation to date

Large Hadron Collider

video

Section 3.3

Atomic Structure

C. Isotopes

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

Section 3.3

Atomic Structure

C. Isotopes

• A particular isotope is represented by the symbol .

e.g. Carbon: What is Z for 12C, 13C and 14C?

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?

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

• WOC page 88 - Q 29, 30