2. History at a Glance Atoms

3. John Dalton 1803 Created Atomic Theory (studied chemical reactions) 1.All elements are composed of tiny indivisible particles called atoms. Atoms cannot be divided (wrong idea.) 2.Atoms of the same element are identical; the atoms of different elements are different. 3.Atoms combine in predictable ratios to make compounds. 4.Atoms are rearranged in chemical reactions.

4. Jingle-Dalton John DALTON said atoms are indivisible, they can’t be divided. (3x) But that’s the wrong idea. (3x)

5. J.J. Thomson Experimented with cathode ray tube. Bent negative particles with an electromagnet Discovered that every atom has negatively charged particles called electrons.

6. Plum Pudding Model J. J. Thomson proposed this model of the atom after the discovery of the proton, a positively charged particle in the atom. Proton (+ charge) Electron (- charge)

7. Jingle- JJ Thomson J.J. Thomson Cathode Ray Experiment. It’s like a battery bending negatively charged particles toward a positive plate Plum-Pudding model (JJ Thomson) Or Cookie Dough Negative Electrons are the Little Chocolates And the Positive Protons are the dough!

8. Ernest Rutherford 1911- Gold Foil Experiment What if I shot alpha particles (radiation- helium nuclei) at an atom? What will I see? Prediction:

9. What he got: Animation for Rutherford's Gold Foil experiment.

10. Gold Foil Experiment (nuclear Atom model) Rutherford shot alpha particles(+) at a thin piece of gold foil and captured particles on a screen around the foil. The screen helped him trace the path of the alpha particles. Most of the alpha particles passed straight through the foil, but some alpha particles were deflected by the center of the atom (+ nucleus). +

12. Rutherford’s Conclusions: There is a central, tiny, dense, positive region of the atom called the nucleus(contains the protons and neutrons) The atom consists mostly of empty space through which electrons move about. The size of the atom is large compared to the size of the nucleus. Ex. Ant (nucleus) in the middle of football field…the rest of the field would be electron cloud.

13. Jingle- Rutherford Ernest Rutherford Gold Foil Experiment Probing Gold Foil with Alpha Particles Some particles Deflect. WHAT? Some particles deflect. But Why? Atoms have a small nucleus with positive charges (PROTONS) surrounded by a large space with negative charges (ELECTRONS)

14. Niels Bohr’s Model (1913) Said electrons travel in orbits (energy levels) around the nucleus We use his model to diagram atoms Central nucleus with electrons located on rings around it. Ex: Silicon

15. Jingle- Bohr Atom The BOHR ATOM! Electrons TRAVEL In Energy orbitals Around the nucleus

16. What is the Modern View of the atom? The atom is mostly empty space. Two regions Nucleus- protons and neutrons. Electron cloud- region where you might find an electron.

17. What is our modern view? The atom is mostly space with a small dense nucleus surrounded by electrons in that space.