1. Warm-Up: October 6 What’s the smallest piece of something called?
How is silver different from sterling silver?
How does science change and grow?
What’s an atom?
What’s a molecule?

2. A journey through time…
Atom!
A journey through time…

3. Originally -
Greeks thought there were four elements: earth, fire, air and water.
Everything was a combination of two or more of the four.

4. Democritus!
Did what we just did. Cut things in half and asked “what if?”
Smallest pieces of matter – atomos (means indivisible)
Suggested that atomos were unique to the material they came from
Cut a mean toga

5. Everybody Hates Democritus
Aristotle and Plato rejected his ideas, re-adopted the idea of four elements.
Democritus’ ideas waited 2,000 years to return.
Thanks a bunch, Aristotle. You jerk.

6. In the meantime… Elements were discovered
Fundamental substances that cannot be broken down further by chemical means
Examples – oxygen, hydrogen, gold, silver, sulfur, aluminum

7. John Dalton! In 1803, developed the atomic theory
All matter is composed of atoms
All atoms of an element are identical, and atoms of different elements have different properties

8. J.J. Thomson!
1897 – discovered negatively charged particles given off by atoms (later named electrons).
His model – the atom was a positively charged pudding, with negatively charged bits (electrons) mixed in like plums.

9. Ernest Rutherford!
Discovered that atoms had a distinct nucleus by shooting positively charged particles at a gold foil in Some went through, some were deflected, some bounced back.
Atoms mostly empty space

10. Niels Bohr! (Nicholas Baker) -
Realized that different electrons had different energies
Saw electrons as “orbiting” the nucleus of the atom – the Bohr Model – the basis of what we use today.
Saw that the chemical properties of an element are determined by the electrons in the outermost orbit

11. Bohr Model in the Movies!
Dr. Manhattan in Watchmen etched a Bohr model of a hydrogen atom into his forehead

12. Today! The electron cloud theory!
You can’t be sure where an electron will be, so it’s all about probabilities.
The picture shows where the electron is likely to be.

13. Dimitri Mendeleev!
Russian chemist. First published table of elements in 1869, based on patterns.
Saw a pattern in the elements, and more importantly, predicted new elements.

14. Mendeleev’s Table: Not exactly it..
He used density, appearance, atomic mass, melting point and how the elements formed compounds to classify his elements.
He did 90% of the work, but missed one thing though…

15. 1913 – Moseley refined it. The last 10%...atomic number!
The Periodic Table of the Elements