1. Chapter 19 Properties of Atoms Periodic Table

2. Unit 1 Investigation III What do you know? In the 5 th century BCE a Greek philosopher named Leucippus and his student, Democritus, stated, “All matter is made up of particles that cannot be divided called atoms.” – What do you think atoms are?

3. Unit 1 Investigation III Essential Question How have chemists thought about the atom through history?

4. Unit 1 Investigation III You will be able to: – Describe some models of an atom and explain how they differ.

5. Unit 1 Investigation III – Atoms are extremely small particles, which cannot be seen, even with microscopes. – All matter is made up of atoms. – Scientists have created models to describe atoms. Models are similar to theories, but often include a picture or physical representation. Notes (cont.)

6. Unit 1 Investigation III – When a model is supported by scientific evidence it is often accepted by the scientific community. – Scientific evidence is a collection of observations that many people have made. Everyone agrees on the same collection of observations. – As new evidence is gathered, models are refined and changed. (cont.)

7. Unit 1 Investigation III Activity Purpose: This lesson will introduce you to various models for the atom that have appeared over the past two hundred years. The descriptions of five models of the atom are on a separate handout. (cont.)

8. Unit 1 Investigation III Five Models of the Atom (cont.)

9. Unit 1 Investigation III Making Sense – Examine the date of the atomic evidence and then put the five models in the correct order of their introduction to the world of science.

10. Correct Order is… Unit 1 Investigation III

11. – An atom is mostly empty space. – The rest consists of a nucleus, which is located in the very center of the atom, and electrons, which are located around the nucleus. – The nucleus is very small (it would be nothing more than a tiny speck in our drawings, if we were to draw it to scale). Notes (cont.)

12. Unit 1 Investigation III – The nucleus is also very dense and consists of two types of particles— neutrons and protons. – A neutron is a neutral particle with no charge on it. – A proton is a positively charged particle. – Tightly bound together, neutrons and protons make a positively charged nucleus. (cont.) Notes (cont.)

13. Unit 1 Investigation III Notes (cont.)

14. Unit 1 Investigation III Check-In Here is a Bohr model of a carbon atom. – List two things this model tells you about atoms. – List something this model does not tell you about atoms.

15. Unit 1 Investigation III Wrap-Up – All matter is made up of extremely small particles called atoms. These particles are too small to be seen even with a microscope. – Science is theoretical and dynamic. Models and theories are continually being revised, refined, or replaced with new models and theories.