1. Ch 4 The Structure of the Atom
4-1 Early Ideas About Matter

2. Aristotle
Said matter is composed of 4 elements

3. Democritus
First to propose a smallest particle
Indivisible particle

4. Dalton’s Atomic Theory
The first two are not always true

5. The Law of Conservation of Mass
Mass (matter) can not be created or destroyed
The mass of the products is equal to the mass of the reactants

6. 4-2 Defining the Atom

7. Atoms One kind of atom is called and element
The smallest particle of an element, that retains the properties of that element
One kind of atom is called and element

8. The size of an Atom
There are more atoms in a teaspoon of water then there are teaspoons of water in the Pacific ocean!
0.1 to 0.5 nanometers
Divide a mm by 1000, divide that by 1000, divide by 10

9. Scanning Tunneling Microscope
Iron atoms on a copper surface
Nanotechnology

10. Subatomic particles Parts that make up the atom
Proton, neutron, electron

11. J. J. Thompson Discovered electrons using a cathode ray tube
Used in TV’s, computer monitors, and radar
J. J. Thompson

12. Cathode Ray Thompson concluded the ray was negative charged
Deflected by a magnet
And made of particles (moved the paddle wheel)

13. Electrons Negative charge, but the atom has no charge
Concluded, atoms must have a + charged particle

14. Thompson’s Plum-pudding model

15. Earnest Rutherford The gold foil experiment Discovered the nucleus
Positive charge
Very small, Very massive

16. Protons Positive charge, equal but opposite of electrons
So a neutral atoms contains equal numbers of each
Mass 1800 times the electron

17. Where is the extra mass? Stable Nucleus?
The mass of an atom is greater than protons + electrons
There must be a third particle
Stable Nucleus?
Like charges repel

18. Neutrons
No charge
Mass equal to proton

19. Strong Nuclear Force One of the 4 Fundamental Forces
Holds protons and neutrons together

20. Even though the nucleus is small, it has 99.9% of the mass
A proton (or a neutron) is about 1800 times more massive as an electron. A marble and a grain of sand

21. Electron Cloud
On this scale, the nucleus would be the size of a marble!
Test Question: Most of the volume of an atom is occupied by which particle?

22. Properties of sub-atomic particles

23. 4-3 How Atoms differ

24. Atomic Number
Protons are in the nucleus

25. How many Electrons does an atom have?
The Atomic number is the number of electrons in a neutral atom

26. Mass Number
The total number of particles (protons and neutrons) in the nucleus of an atom
How many neutrons does sodium have?

27. Isotopes
Atoms of the same element with different numbers of neutrons

28. How to determine the number of neutrons in an atom?

29. Natural Abundance of Isotopes
The relative abundance of each isotope is constant

30. Atomic Mass Units
1 amu is 1/12 the mass of a Carbon-12 atom

31. Atomic mass and Mass Number
Mass number is different from atomic mass (aka average atomic mass & atomic weight)

32. Average Atomic Mass The average mass of all the isotopes of an element
Based on the percentage of each isotope

33. 4-4 Unstable Nuclei and Radioactive Decay

34. Nuclear Reaction
A reaction that involves a change in an atom’s nucleus
Can change the identity of the atom

35. Radioactivity Radioactivity – The spontaneous emitting of radiation
Radiation – The rays and particles emitted by radioactive material

36. Radioactive Decay Unstable nuclei lose energy of emitting radiation
Often a different element

37. Types of Radiation

38. Alpha Radiation An alpha particle, two protons and two neutrons
2+ charge
Equivalent to a helium nucleus
Can be blocked by paper

39. Beta Radiation Fast moving beta particles, an electron Charge 1-
In carbon-14 decay, a neutron decays in a proton

40. Gamma Radiation High energy gamma rays have no mass
Turned Bruce Banner into the Hulk

41. Characteristics of Radiation

42. Nuclear Stability
Atoms are unstable if they have too many or too few neutrons
They undergo radioactive decay to become stable

43. The End