1. History of Atoms Notes Use the information on each slide to fill in the blanks on the student notes.

2. History of Atoms Democritus Who first thought of the atom? The Greek philosopher Democritus (about 400 BC) – he thought if you cut an object over and over and over again, there would eventually be a piece that you couldn’t cut anymore. He called that piece an atom. In Greek, atom means “not to be cut” or “indivisible”. Democritus by Agostino Carracci (1557- 1602)

3. History of Atoms John Dalton The Atomic Theory John Dalton was an English Scientist. In 1803 he proposed the atomic theory that says: -Atoms cannot be divided -Atoms are invisible -All elements are made of atoms -Atoms of the same element are the same -Atoms of different elements are different -Molecules are formed by two or more atoms joined together

4. History of Atoms Joseph J. Thomson What are atoms made of? In 1897 a scientist named Joseph J. Thomson was experimenting with gases and electricity and discovered that atoms have negatively and positively charged particles. The negatively charged particles are called electrons and the positively charged particles are called protons.

5. Lesson 11: History of Atoms Ernest Rutherford What else are atoms made of? Ernest Rutherford discovered in 1908 that atoms are mostly made of empty space! In the center of the atom is a dense nucleus of protons surrounded by electrons. In fact, if the nucleus of an atom was the size of a pea, the atom would be as big as a football stadium! The electrons would be flying around the outside of the stadium, and the rest of the atom would be empty space!

6. Lesson 11: History of Atoms Ernest Rutherford Imagine one of these in the middle of there. All the rest of the stadium is empty space and the electrons are flying around the outside.

7. Lesson 11: History of Atoms Niels Bohr What do atoms look like? In 1913, Niels Bohr proposed that the atoms look like a solar system, with the protons in the nucleus acting like the sun, and the electrons flying around the nucleus like planets orbiting the sun. Proton Neutron Electron

8. Lesson 11: History of Atoms Werner Heisenberg What do atoms look like? In 1926, Werner Heisenberg proposed that electrons don’t really fly all around the atom. He said that electrons had certain spots they floated around in called orbitals (kinda like balloons). http://lifesciencereality.wordpress.co m/2008/05/10/models/

9. Lesson 11: History of Atoms James Chadwick The Last Piece In 1932, James Chadwick discovered that atoms also contain neutrons. Neutrons do not have a charge they are “neutral”. The neutrons and the protons make up the nucleus, or the center of the atom.