3. Unit 3 Development of the Modern Atomic theory
Democritus & Dalton
Schrodinger
Rutherford
Thomson
Bohr

5. Development of the Atomic Theory

6. Democritus
Greek Philosopher who proposed that matter could not be divided infinitely. He called this smallest particle the atom. Democritus said that atoms could not be created, destroyed, or further divided.

7. Democritus 460-370 B.C. Greek Philosopher
He called nature’s basic particle an atomos, based on the Greek word “indivisible.”
Had no evidence so people didn’t take him seriously.
He considers education to be the noblest of pursuits, but cautioned that learning without sense leads to error. (THERE MUST BE A POINT!!!)
Aristotle said empty space did not exist & rejected Democritus; said matter was EARTH, WATER, AIR & FIRE

8. John Dalton
Took the idea that atoms cannot be divided from Democritus. John Dalton was born in England in Dalton studied numerous chemical reactions and was able to come up with some ideas to describe the way that elements and atoms behave. He made careful measurements and observations while studying the chemical reactions.

9. Dalton’s Atomic Theory
1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. 3. Atoms of different elements combine to form compounds in whole number ratios. 4. Chemical reactions occur when atoms are separated, joined, or rearranged.

10. John Dalton 1803 Dalton’s Atomic Theory
All elements are composed of tiny indivisible particles called atoms.
Element A
2. Atoms of the same element are identical. The atoms of any one element are different from those of any other elements.

11. Dalton’s Atomic Theory
3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds.

12. Dalton’s Atomic Theory
4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

13. Joseph John (J.J.) Thomson
Joseph John Thomson was an English Physicist born in He is known for his work on the conduction of electricity with gases. Thomson discovered the electron in 1897 with his cathode ray experiment. He said that electricity was conducted by small particles called electrons, which are part of an atom. The discovery of the electron disproved Dalton’s theory that atoms could not be divided into smaller particles. Thomson came up with the “plum pudding”or “chocolate chip” model of the atom because he said the atom was positive with negative particles all over.

14. J.J. Thomson 1897 (with Crookes & Millikan)
discovery of the electron (e-)
disproved Dalton’s theory; atoms DID have smaller parts after all
Used a cathode ray tube to prove that there were charged particles (stream of (-) particles) within the atom

15. Thomson Model Plum pudding model aka chocolate chip cookie model
Millikan found out that electrons were negatively charged and had a mass of 1/1840 of a hydrogen atom
Plum pudding model aka chocolate chip cookie model

16. Ernest Rutherford Rutherford Model
Ernest Rutherford was born in New Zealand in He discovered the nucleus of an atom in 1907 with his Gold Foil Experiment. He said that the nucleus was positively charged, dense, and contained most of the mass of an atom. Rutherford also thought that electrons were zooming around the outside of the nucleus in the empty space. He was awarded the Nobel Prize in 1908 for his work in Chemistry.
electron
nucleus
Empty space
Rutherford Model

17. Nucleus
Empty Space
Electrons

18. Rutherford said, “Atoms have a nucleus!”
Dense & positively charged
Contains most of the mass of the atom
Contains the protons (positive charge; heavy
Electrons are around the outside of the nucleus flying around the empty space

19. James Chadwick Discovered the neutron in 1932 Has a neutral charge
Found in the nucleus
About ½ of the mass of the nucleus
Wanted to know where the extra mass was coming from in an atom; shot beryllium
Eventually led to experiments to bombard atoms with neutrons –> uranium  bombs!

20. Niels Bohr
Niels Bohr was a student of both J.J. Thomson and Ernest Rutherford at Cambridge University. Bohr wondered why the positively charged nucleus and the negative electrons were not colliding into one another within an atom. His explanation was that the electrons were orbiting the nucleus much like the Earth orbits the sun. This is called the “planetary model” of the atom. He said that electrons would jump energy levels (orbits) when electricity is applied to the atom. He was awarded the Nobel Prize in 1922 in Physics for his work on the model of the atom.

21. Niels Bohr - 1913 Created the Bohr model
Electrons travel in definite orbits/ energy levels around the nucleus
aka “Planetary Model” – orbit the nucleus like planets around the sun
Electrons have fixed amounts of energy “quanta”
Low energy  closer to nucleus
High energy  further from nucleus

22. Bohr Model

23. Werner Heisenberg, 1927
It’s impossible to know both the location and the motion of an electron at the same time
Heisenberg Uncertainty Principle

24. Erwin Schrodinger
Erwin Schrodinger was born in Austria in In 1926, he came up with the idea that electrons do not orbit the nucleus of an atom in circular motions, but rather in a cloud, or wave. The electrons are negatively charged and dispersed throughout the empty space of an atom. Their location in time and space can be predicted to a certain degree. Schrodinger is the father of modern Quantum Theory and is the most current model of the atom that we use today.
Schrodinger’s Model of the Atom

25. Schrodinger’s Cat

26. Quantum Mechanical Model (aka wave mechanical model)
Erwin Schrodinger – 1926
Electrons DO NOT orbit the nucleus
Electrons DO have quanta of energy that determine placement in an atom

27. Electron Cloud
Area where there is a high probability that the electron will reside there 90% of the time

28. Video Links to Experiments
JJ Thomson’s Cathode Ray Tube
How does it work?
Rutherford’s Gold Foil Experiment
What did he do?