2. Opener: Describe the earliest cell phone you remember. How have cell phones changed since then? Why is it important for cell phone developers to know what the older versions were like?

4.  It’s time for… THE HISTORY OF THE ATOM

5. Democritus 400 B.C. Proposed that matter is made of about 100 basic kinds of tiny particles he called “atomos” that can’t be divided into smaller particles. Nobody believed him.

6. His experiments with gases suggested that matter was composed of tiny particles. He renewed interest in the idea of atoms.

7. Antoine Lavosier 1780 Known as the Father of Modern Chemistry Developed the theory of Conservation of Matter Antoine Modern chemistry

8. John Dalton 1803 Atoms are all solid with uniform density (like a gum ball) Atoms are the smallest particles of nature. All atoms of the same element are identical. All atoms are indivisible Atoms of different sizes can combine to make compounds. An atom, according to Dalton.

9. Marie Curie 1898  Credited with the discovery of the first radioactive elements.  Theorizes that theses elements emit invisible rays called “radiation”  First person to win Nobel Prizes in TWO different sciences (chemistry and physics).  Discredits part of Dalton’s theory (indivisible atoms)  Atoms must have smaller components

10. Credited for the discovery of the electron, because he realized the “beam of light” in a Crookes tube was really made of negative particles. Realized that electrons were smaller than atoms. This information discredited part of Dalton’s atomic theory Developed the “Plum Pudding” model of the atom

11. Experimented with magnets -

12. Experiment #2 +

13. Conclusions? The stream of particles was … Negative  Overall, atoms are...  Neutral  Therefore, atoms must also contain charges that are...  Positive

14. Plum (electrons) Pudding (positive stuff) Today, it would probably be called the “Chocolate Chip Cookie” Model

15. Max Planck 1900 Developed Quantum Theory. He discovers that energy is not given off in continuous amounts. Instead, energy is released in small packets that he calls “quanta”. This idea contradicts our common-sense ideas about energy and matter – but it turns out to be correct! Energy acts like a particle!

16. Ernest Rutherford 1910 Performed Gold Foil Experiment. Discovered that atoms had a nucleus! Disproved “Plum Pudding” model. Won Nobel Prize for Chemistry.

17. The Gold Foil Experiment Bombard thin piece of gold foil with alpha particles Result: some are deflected while others are unaffected What does it all mean?

46. Dense, positively charged nucleus. Electrons surround the nucleus like bees around a hive. Atoms are mostly empty space. Problem: Why didn’t electrons get pulled into the nucleus?

47. Neils Bohr 1913 Extended Quantum Theory to electrons in atoms! Electrons are in certain orbits at a specific distance from the nucleus. Only certain orbits were “allowed”. If an electron stayed in its orbit, it didn’t lose any energy and would not fall into the nucleus.

48. Atomic Line Spectra Hydrogen Gas Prism or diffraction grating Expected to see a nice progression of color just like normal BUT…..

49. Atomic Line Spectra Gas such as Neon or Hydrogen Prism or diffraction grating Instead he got just a few discrete lines of color!

50. Niels Bohr Planetary Model Compares electrons orbiting the nucleus of an atom to planets orbiting around the sun. Electrons occupy distinct orbitals. Orbitals have certain energies and distances from the nucleus. Bohr’s theory explains how light is given off – a huge success!

51. For Electrons Nucleus 3  2 2  1 3  1

52. Heisenberg/Schrodinger Quantum Mechanical Model/ Electron Cloud Model Regions where electrons are most likely found are called “electron clouds”. Different types of orbitals have different shapes and different levels of energy.

54. James Chadwick 1932 Established the existence of the neutron. neutron

55. 1980’s The first atoms are seen with scanning tunneling microscopes