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 –viewed atoms as tiny, solid balls

5. Discovered the electron
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 + -
By adding an electric field he found that the moving pieces were negative

21. Thomson’s “Plum Pudding” Model

22. Democritus, Dalton, Thomson Video

23. Ernest Rutherford *
Discovered protons and the nucleus

24. Ernest Rutherford
He showed that atoms have (+) particles in the center and are mostly empty space
He called the (+) particles protons
He called the center of the atom the nucleus

26. Alpha particles (+) bounce off of the positively-charged nucleus, but they go straight through the electron cloud.

27. Rutherford’s Contribution
The atom is mostly empty space.
The nucleus is a small, dense core with a positive charge.

28. Gold Foil video

29. Rutherford’s Atomic Model

30. 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

31. 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

32. 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

33. 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

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

35. Counting Atoms
Nuclear Symbol Notation

36. 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

37. 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

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

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

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

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

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