1. Atoms

2. Sizes of Atoms Atoms are so small it would take about 1 million of them lined up in a row to equal the thickness of a human hair.

3. Dalton’s Atomic Model Believed matter was made up of atoms Also thought matter was only one kind of atom Iron makes iron, gold makes gold Become the atomic theory of matter

4. Thomson’s Model He discovered electrons by conducting an experiment that dealt with positive and negative charges Electron- invisible, negatively charged particle located in a cloudlike formation that surrounds the nucleus of an atom

5. Thomson’s Model

6. Rutherford- The Nucleus He discovered that atoms have a positively charged center called a nucleus, he named the particles in the nucleus protons Nucleus- positively charged, central part of an atom Proton- positively charged particle located in the nucleus of an atom

7. Rutherford- The Nucleus

8. The Neutron Rutherford was confused about the extra mass in the atom that wasn’t accounted for Chadwick his student answered this problem by discovering the neutron Neutron- an uncharged particle located in the nucleus of an atom

9. Improving the Atomic Model Niels Bohr found evidence that electrons in atoms are arranged according to energy levels Lower energy levels are closest to the nucleus, Higher energy levels are farther from the nucleus

10. Modern Atomic Model

11. The Electron Cloud Electron Cloud- a spherical cloud of varying density surrounding the nucleus The varying density shows where an electron is more or less likely to be Usually the electron cloud has a radius 10,000 times that of the nucleus

12. The Electron Cloud