1. Atoms and Atomic Theory
Essential Questions: How and why has the Atomic Theory changed over time? How can we describe the molecular motion of the states of matter?

2. Atoms
Matter is anything that takes up space and has mass. All matter is made of atoms.
Atoms are the basic building blocks of matter. They make up everything around us; Your desk, the board, your body, everything is made of atoms!
Atoms are too small to see without powerful microscopes.

3. Atomic Structure
There are two basic components in every atom: Electron Cloud Nucleus

4. Subatomic Particles Three subatomic particles make up every atom:
Charge
Location
Proton
Positive (+)
Nucleus or “Core”
Neutron
No Charge (0)
Electron
Negative (-)
Electron Cloud

5. Subatomic Particles Electron Cloud: Electrons orbit the nucleus.
Nucleus or “Core”:
Protons and Neutrons are found in the nucleus.

6. Atomic Theory
Changes over time…

7. Atomic Theory
Because we can not see atoms, we use models to teach and learn about atoms.
The atomic theory has changed over time as new technologies have become available.
Remember: Scientific knowledge builds on past research and experimentation.

8. In 1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them.

9. Atomic Theory Timeline
Scientist
Information
Model
John Dalton
All matter is made of atoms. Atoms are too small to see, indivisible and indestructible. All atoms of a given element are identical.

10. Atomic Theory Timeline
Scientist
Information
Model
J.J Thompson
Discovered the negative electron, and predicted that there also must be a positive particle to hold the electrons in place.

11. Atomic Theory Timeline
Scientist
Information
Model
Ernest Rutherford
Discovered the nucleus of an atom and named the positive particles in the nucleus “protons”. Concluded that electrons are scattered in empty space around the nucleus.

12. 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

13. Atomic Theory Timeline
Scientist
Information
Model
Neils Bohr
Concluded that electrons are located in planet-like orbits around the nucleus in certain energy levels.

14. Scientist Information Model
(Many Scientists!)
The Modern Atomic Theory
Electrons do not orbit the nucleus in neat planet-like orbits but move at high speeds in an electron cloud around the nucleus.

15. Think-Pair-Share!
Take a minute to read the essential question as I read it aloud: “How and why has the Atomic Theory changed over time?” After you have jotted down your notes in the space on your guided notes, exchange your thoughts with your partner. We will have share-outs and discuss the answer.