1. Atomic Structure

2. Democritus 460 BC Greek Philosopher
Suggested world was made of two things – empty space and “atomos”
Atomos – Greek word for uncuttable
2 Main ideas
Atoms are the smallest possible particle of matter
There are different types of atoms for each material

3. John Dalton’s Atomic Theory 18042
John Dalton’s Atomic Theory 1804
1. All matter is made of atoms.
2. Atoms of one element are all the same.
3. Atoms cannot be broken down into smaller parts
4. Compounds form by combining atoms

4. Dalton’s Early Atomic Model
“Billiard Ball” model
he envisioned atoms as solid, hard spheres, like billiard(pool) balls, so he used wooden balls to model them

5. J.J. Thomson 1897 Discovered the electron
He was the first scientist to show the atom was made of even smaller things

6. JJ Thomson
Used the Cathode ray tube to discover electrons

7. Thomson’s Experiment
Voltage source - +
Vacuum tube
Metal Disks

8. Thomson’s Experiment
Voltage source - +

9. Thomson’s Experiment
Voltage source - +

10. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

11. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

12. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

13. - + Thomson’s Experiment
Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

14. Thomson’s Experiment
Voltage source
By adding an electric field

15. Thomson’s Experiment
Voltage source + -
By adding an electric field

16. Thomson’s Experiment
Voltage source + -
By adding an electric field

17. Thomson’s Experiment
Voltage source + -
By adding an electric field

18. Thomson’s Experiment
Voltage source + -
By adding an electric field

19. Thomson’s Experiment
Voltage source + -
By adding an electric field

20. Thomson’s Experiment - Voltage source -+ - -
Adding an electric field cause the beam to move toward the positive plate.
Thomson concluded the beam was made of negative moving pieces.

21. Thomson’s “Plum Pudding” Atom Model

22. Democritus, Dalton, Thomson Video

23. He is credited with the discovery of protons in an atom.
Eugen Goldstein 
Using a cathode ray tube he discovered canal rays which are beams of positively charged particles.
He is credited with the discovery of protons in an atom.
Canal Rays discovery

24. Millikan’s Oil Drop Experiment
Determined the charge on an electron
Used Thomson’s charge to mass ratio to calculate the mass of an electron
Millikan’s Oil Drop Experiment
Millikan’s Oil Drop Experiment – another video

25. Ernest Rutherford
discovered the nucleus of a gold atom with his “gold foil” experiment

27. Using J.J Thomson’s Plum Pudding atomic model, Rutherford predicted the alpha particles would pass straight though the gold foil. That’s not what happened.

28. Gold Foil Experiment Results
most alpha particles go straight through the gold foil
A few alpha particles are sharply deflected

29. Rutherford’s Conclusion
The atom is mostly empty space.
There is a small, dense center with a positive charge.
Rutherford discovered the nucleus in atoms

30. Rutherford’s Contribution to the Atomic Theory
The atom is mostly empty space.
The nucleus is a small, dense core with a positive charge.

31. Gold Foil video

32. Rutherford’s Atomic Model

33. Structure of the Atom
Atom – smallest particle of an element that can exist alone
Two regions of an atom
Nucleus
Center of atom
Protons and neutrons
Electron “cloud”
Area surrounding nucleus
containing electrons

34. Structure of the Atom
Proton – Positive charge (+), 1 atomic mass unit (amu); found in the nucleus
amu -Approximate mass of a proton or a neutron
Neutron – Neutral charge (0), 1 amu; found in the nucleus
Electron – Negative charge (-), mass is VERY small

35. Counting Atoms Atomic Number Mass Number (Atomic Mass)
Number of protons in nucleus
The number of protons determines identity of the element!!
Mass Number (Atomic Mass)
Number of protons + neutrons
Units are g/mol

36. Counting Atoms Isotopes
Atoms of the same element with varying number of neutrons
Different isotopes have different mass numbers because the number of neutrons is different

37. Composition of the atom video
Start at 3:25

38. Counting Atoms
Nuclear Symbol Notation

39. Atoms
Protons have a positive (+) charge and electrons have a negative (-) charge
In a neutral atom, the number of protons equals the number of electrons, so the overall charge is zero (0)
Example/ Helium, with an atomic number of 2, has 2 protons and 2 electrons when stable

40. Ions
In a neutral atom
Atomic number = # of protons = #of electrons
Sometimes atoms will gain or lose electrons and form IONS
Because an electron has a negative charge:
When an atom GAINS electrons it becomes NEGATIVE
When an atom LOSES electrons it becomes POSITIVE

41. Ions
Cation = a positive ion
Anion = a negative ion

42. Let’s Practice Aluminum (Al) (no periodic table) Protons = 13
Electrons =
Neutrons = 14
Atomic Number =
Atomic Mass =

43. Let’s Practice w/ nuclear symbol notation
Nuclear Symbol notation (no periodic table)
Protons =
Electrons =
Neutrons =
Atomic Number =
Atomic Mass =
108 Ag 47

44. Let’s Practice w/ isotopes
use the periodic table
Protons =
Electrons =
Neutrons =
Atomic Number =
Atomic Mass =
Uranium-235

45. Let’s Practice with Ions
Use the periodic table
Charge =
Protons =
Electrons =
Neutrons =
Atomic Number =
Atomic Mass = 39 K 1+