Development of Atomic Theory (11.1)

1. Development of Atomic Theory (11.1) Famous Scientists and their theories…

2. Democritus 440 BCE – thought that if you kept cutting an object in half, the piece would eventually get too small to cut. This particle is called an “atom”. Thought that atoms were small hard particles made of a single material formed into different shapes and sizes.

3. Aristotle Thought you would NEVER end up with a particle that couldn’t be cut… He was WRONG!!!

4. John Dalton • Atomic Theory was published in 1803 • All substances are made of atoms. Atoms cannot be divided. • Atoms of the same element are exactly the same. • Atoms join with other atoms to make different substances. Not all of his theory was correct!...

5. J. J. Thomson • Discovered that there are smaller particles WITHIN an atom. Disproved Dalton’s theory that atoms could be divided into smaller particles. • Used a cathode-ray tube and discovered that ELECTRONS were spread throughout the atom, like plums in plum pudding (or chocolate chips in ice cream. • Created the plum-pudding model. Plum- Pudding model: Electrons were located throughout an atom like chocolate chips in ice cream.

6. Ernest Rutherford 1909- Created an experiment where some atom particles were deflected instead of passing through gold foil. This led to the discovery that atoms are mostly empty space with a very dense nucleus. When he calculated the diameter, the nucleus was 100,000 times smaller than the diameter of the atom.

7. Niels Bohr 1913 – studied how atoms react to light. Proposed that electrons move around the nucleus in energy levels. Electrons were able to “jump” to different levels. - + - N + N N + -

8. Schrodinger and Heisenberg Explained that electrons do not travel in definite paths and their paths cannot be predicted. Proposed that there are regions where electrons are likely to be found called the “electron cloud”. Erwin Schrodinger Werner Heisenberg