1. + ATOMIC THEORY

2. + Democritus Atom Democritus is an Ancient Greek philosopher born in Abdera, Thrace, Greece He was said to be the first step toward the current atomic theory. Hypothesized that all matter is composed of tiny indestructible units, called atoms.

3. + His atomic theory contradicted the idea that matter can be infinitely divided. According to him, atoms cannot be divided forever. In the long run, the object will become so small and invisible that you cannot divide it any further. He said that these indivisible invisible particles are ATOMS. The word “atomos” means not to be cut or indivisible.

4. + Aristotle 384 to 322 B.C. A popular Greek Philosopher Disagreed with Democritus ideas He believed that you would never end up with an indivisible particle. His ideas were proven incorrect. He had such a strong influence. So people believed him and ignored Democritus.

5. + John Dalton English, chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory.

6. + 5 POINTS of Dalton’s Theory All matter consists of tiny particles called atoms. These are indivisible and indestructible. All atoms of a given element are identical in mass and properties. The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative atomic weights.

7. + Compounds are formed by a combination of two or more different kinds of atoms. Compounds are pure substances. They can’t be separated into elements by phase changes because the atoms of different elements are bonded to one another and are not easily separated from one another. A chemical reaction results to rearrangement of atoms.

8. + Joseph John “JJ” Thomson British physicist Discoverer of Electrons Discoverer of Isotopes Isotopes have the same number of protons and electrons, thus they have the same atomic number and the same chemical reactions. But they have different numbers of neutrons giving them different atomic masses. Some isotopes are heavier or lighter than others.

9. + Thomson’s Cathode-Ray Tube

10. + Proposed the Plum pudding model Awarded the 1906 Nobel Prize in Physics

11. + PLUM PUDDING MODEL Also known as the “Chocolate Chip Cookie or Blueberry Muffin Model.” Atom is composed of electrons surrounded by a soup of positive charge to balance the electron’s negative charge, like negatively- charged “plums” surrounded by positively-charged “pudding”.

12. + Sometimes visualized as having a cloud of positive charge, a striking contrast to the most recent atomic model, which describes the positive nucleus to be surrounded by an electron cloud. Electrons were free to rotate within the cloud of positive substance. These orbits were stabilized in the model by the fact that when an electron moved farther from the center of the positive cloud, it felt a larger net positive inward force, because there was more material of opposite charge, inside its orbit.

13. + Ernest Rutherford New Zealand chemist and physicist Father of Nuclear Physics Discovered that atoms have their positive charge concentrated in a very small nucleus. Rutherford Model

14. + Gold Foil Experiment Discoverer of proton Awarded Nobel Prize in Chemistry in 1908 Widely credited as splitting the atom in 1917 Leading the first experiment to “split the nucleus”

15. + Gold Foil Experiment

16. + The unexpected results of the experiment demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of the plum pudding model of the atom, and the development of the Rutherford (or planetary) model.

17. + Bohr’s Model Also known as the planetary model Neutrons and protons are in the nucleus while the electrons are orbiting the nucleus Electrons are able to jump from one orbit to another

18. + Electron Cloud Model 1920 Consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels. Erwin Schrodinger and Werner Heisenburg developed probability functions to determine the regions or clouds in which electrons would most likely be found.