1. Introduction to Atoms 8th Grade Science
© Fall 2005, Pflugerville ISD, 8th Grade

2. Introduction to Atoms PISD PowerPoint Lessons Developed By
8th Grade Science
Introduction to Atoms
PISD PowerPoint Lessons
Developed By
Ryan Gross, Park Crest Middle School
Edited By
Kenn Heydrick, Coordinator of Science & Health
© Fall 2005, Pflugerville ISD, 8th Grade

3. Development of the Atomic Theory
Introduction to Atoms
Section 1:
Development of the Atomic Theory
Section 2:
The Atom
Unit A : Chapter 2

4. Development of the Atomic Theory
What Do You Think?
Imagine that you have cut a penny in half. Then, you take one piece and half it again. Will this continue forever, or will you come to a point where no more cutting is possible?
Unit A : Chapter 2

5. Development of the Atomic Theory
Democritus was a Greek philosopher who theorized that all matter was made of invisible particles called atoms.
Democritus of Abdera,
about BCE
Unit A : Chapter 2

6. Development of the Atomic Theory
His views contrasted those of Aristotle, who believed in the four elements; earth, water, air, fire.
Unit A : Chapter 2

7. Development of the Atomic Theory
Most of our knowledge of Democritus comes from negative remarks about him in others’ writings.
Unit A : Chapter 2

8. Development of the Atomic Theory
Dalton, a British chemist and teacher, did studies and experiments in weather, colorblindness, and gases.
John Dalton
Unit A : Chapter 2

9. Development of the Atomic Theory
He noticed that elements combine in specific proportions to form compounds, and theorized that their atoms combine at the same proportions
Unit A : Chapter 2

10. Development of the Atomic Theory
Thomson’s experiments using a cathode-ray tube showed that smaller particles make up atoms
Joseph John
“J.J.” Thomson
Unit A : Chapter 2

11. Development of the Atomic Theory
Thomson received the Nobel Prize in physics in 1906 for his discovery of the electron.
Unit A : Chapter 2

12. Development of the Atomic Theory
Rutherford, a former student of Thomson’s from New Zealand, tested his teacher’s theories in his Gold Foil Experiment.
He expected his alpha particles to go straight through the foil, and most of them did.
Ernest Rutherford
Unit A : Chapter 2

13. Development of the Atomic Theory
But some of the particles were deflected or bounced straight back!
This showed that a nucleus with a positive charge makes up the center of an atom.
Rutherford’s Gold Foil Experiment
Unit A : Chapter 2

14. Development of the Atomic Theory
Bohr, a Danish scientist who worked with Rutherford, described the motion of electrons around the nucleus.
Niels Bohr
Unit A : Chapter 2

15. Development of the Atomic Theory
Bohr said that electrons orbit the nucleus at specific energy levels, and can move from one level to another.
Bohr’s Atomic Model
Unit A : Chapter 2

16. Development of the Atomic Theory
To do this, Bohr said, the electrons must absorb or release energy, often in the form of light.
Unit A : Chapter 2

17. Development of the Atomic Theory
Erwin Schrödinger and Werner Heisenberg’s work with the uncertainty principle explained that electrons do not travel in orbits.
In fact, the exact path of a moving electron cannot be predicted.
Schrödinger & Heisenberg
Unit A : Chapter 2

18. Atomic Theory Timeline
Scientist
Information
Model
James Chadwick
Discovered that neutrons were also located in the nucleus of an atoms and that they contain no charge.
Neutrons

19. Development of the Atomic Theory
The current atomic theory states that there are regions inside an atom where electrons are likely to be found.
These regions are called electron clouds.
Electron Cloud Model
Unit A : Chapter 2

20. The Atom
What Do You Think?
What is the smallest thing you have ever seen? How does it compare to the size of an atom?
Unit A : Chapter 2

21. Parts of the Atom
The nucleus is the small, dense, positively charged center of the atom.
Protons are positively charged particles in the nucleus
Neutrons are particles in the nucleus that have no charge
Nucleus
Unit A : Chapter 2

22. Parts of the Atom
The current atomic theory states that there are regions inside an atom where electrons are likely to be found.
These regions are called electron clouds.
Electron Cloud Model
Unit A : Chapter 2

23. The Atom
What Do You Think?
What are some differences you use to tell one of your classmates from another?
Unit A : Chapter 2

24. Atomic Number- the Number of Protons
The Helium atom has two protons in its nucleus.
This means that it has the atomic number 2.
Helium Atom
Unit A : Chapter 2

25. Atomic Number- the Number of Protons
The Lithium atom has three protons in its nucleus.
This means that it has the atomic number 3.
Lithium Atom
Unit A : Chapter 2

26. Atomic Mass Number- Protons plus Neutrons
The Helium atom has two protons and two neutrons in its nucleus.
This means that it has the atomic mass number 4.
Helium Atom
Unit A : Chapter 2

27. Atomic Mass Number- Protons plus Neutrons
The Lithium atom has three protons and four neutrons in its nucleus.
This means that it has the atomic mass number 7.
Lithium Atom
Unit A : Chapter 2

28. Atomic Mass Number- Isotopes
Notice that these isotopes of hydrogen have the same number of protons, but different numbers of neutrons.
Isotopes of Hydrogen
Unit A : Chapter 2

29. Atomic Mass Number- Isotopes
These isotopes are also known as Hydrogen-1, Hydrogen-2, and Hydrogen-3
Unit A : Chapter 2

30. Let’s Review!
- 1 -
In the history of science, what are some ways scientists have described the atom?
Unit A : Chapter 2

31. What are the parts of an atom, and how is an atom structured?
Let’s Review!
2 -
What are the parts of an atom, and how is an atom structured?
Unit A : Chapter 2

32. Let’s Review!
3 -
What is the atomic number of an atom? How is this different from the atomic mass number?
Unit A : Chapter 2

33. Atomic Theory Web Sites to Visit
Unit A : Chapter 2