Developing the Atomic Theory

1. Developing the Atomic Theory Text 5.1: Page170-175

2. Agenda • Just How Small is an Atom? • Developing Atomic Theory • Modern Model • Check & Reflect • Assignment – Timeline of the Development of Atomic Theory

3. Learning Goals • By the end of the class, we should be able to • Describe how the model of the atom has changed over time • Describe the structure of the atom according to modern atomic theory • Calculate the number of protons, neutrons and electrons in an atom based on the periodic table

4. Minds On: Just How Small is an Atom?

5. Development of Atomic Theory • Philosophers of Ancient Greece reasoned there were 4 basic forms of matter • Fire, Water, Earth and Air

6. Development of Atomic Theory • In ancient China they reasoned there were 5 basic forms of matter • Fire, water, wood, metal and earth

7. Development of Atomic Theory • 440 BCE, Greek philosopher Democritus also hypothesized about the atom • He thought that breaking down rock into powder would reduce it to tiny bits of matter that couldn’t be broken down any more • Wasn’t popular at time because there was no experimental evidence to support his claim

8. Modern Atomic Theory • Rooted in the idea that an understanding of atoms and their structure can help us predict the properties of matter • Began with John Dalton, who reconsidered the ancient idea that each different kind of element is composed of a different type of atom

9. Dalton’s Atom • Dalton’s theory stated: • All matter is made of small, invisible particles called atoms • Atoms of different elements have different properties • Atoms of different elements can combine in specific ways to form new substances • All atoms of an element are identical in proprieties such as size and mass

10. Sound Familiar?

11. Building Off Dalton… • He had it right! • All matter is made of small, invisible particles called atoms • Atoms of different elements have different properties • Atoms of different elements can combine in specific ways to form new substances • All atoms of an element are identical in proprieties such as size and mass

12. The Atom • JJ Thompson researched the idea that atoms may be made of smaller parts that are charged • Experiment included using electric currents in glass tubes called cathode ray tubes.

13. The Atom • JJ Thompson researched the idea that atoms may be made of smaller parts that are charged • Through experimentation he determined atoms must be made of both + and – charged pieces • We now know these to be electrons (-) and protons (+)

14. The Atom • Ernest Rutherford expanded on the idea of the size of the parts of the atom • He calculated through experimentation that there was a tiny nucleus in the center of orbiting electrons

15. Finishing Touches • James Chadwick suggested in the nucleus also contained neutral particles • Now known as neutrons • Niels Bohr suggested electrons traveled in shells or energy levels • With each shells having a specific number of electrons in them • Also now sometimes described as “electron clouds”

16. So What’s the Big Picture?

17. So What’s the Big Picture?

18. More Info on the Atom • Note: Atomic Mass= # Protons + # Neutrons

19. Check & Reflect • Skim & Scan Chapter 5.1 • Complete questions 1-6 on page 175 ‘Learning Checkpoint’. • Answer in complete sentences in your notebook.

20. Assignment - TimeToast • Create a timeline of the development of the atomic theory. • Include pictures, text, and info on two scientists per time period. • Use p.g. 176 to help you…