1. Atomic Theory
Models and Particles

2. Greek Idea “qualitative” Democritus
(400 B.C.)
Matter is made up of indivisible particles
(atomos)

3. Dalton’s Atomic Theory 1808
All matter is composed of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; different elements differ in size, mass, and other properties.

4. Dalton’s Atomic Theory
Atoms cannot be subdivided, created, or destroyed
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

5. Dalton’s Atomic Theory
Law of definite proportions: A chemical compound contains the same elements in the same ratio no matter the source or size of the sample.
Example : water H2O ratio of 2:1
And
Law of Multiple proportions: The same elements can combine in different proportions to form different compounds.
Example : water H2O and Hydrogen peroxide H2O2

6. Dalton’s Atomic Theory
Law of conservation of mass – Matter (mass)
cannot created nor destroyed, chemically nor
physically.
Example: Carbon + Oxygen = Carbon monoxide
12.00g g = 28.00g

7. 1808
John Dalton’s model of the atom

8. Thomson’s Model 1897 Discovered electrons using the Cathode Ray Tube
Atoms were made of positive stuff
Negative electron floating around
“Plum-Pudding” model or raisin bun

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

10. Voltage source - +

11. Voltage source - +

12. Voltage source - +

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

14. Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

15. Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

16. Voltage source - +
Passing an electric current makes a beam appear to move from the negative to the positive end

17. By adding an electric field
Voltage source
By adding an electric field

18. Voltage source + -

19. Voltage source + -

20. Voltage source + -

21. Voltage source + -

22. Voltage source + -

23. Voltage source + -
By adding an electric field he found that the moving pieces were negative

24. Other particles
Later Thompson discovered the Proton – which is positively charged and 1840 times heavier than the electron
Neutron - no charge but the same mass as a proton – by J. Chadwick

25. Ernest Rutherford 1911 Ernest Rutherford Experimented with gold foil
He expected that the alpha particles would be deflected a small amount if Thomson’s model was correct.

26. He Expected
The alpha particles to pass through without changing direction very much.
Because…?
…the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles.

27. What he expected

28. Because

29. He thought the mass was evenly distributed in the atom

30. Since he thought the mass was evenly distributed in the atom

31. What he got

32. How he explained it Atom is mostly empty. Small dense, positive piece+
Atom is mostly empty.
Small dense, positive piece
at center.
Alpha particles are deflected by it if they get close enough.

33. Like Charges repel & unlike attract+

34. Rutherford’s Model
Discovered dense positive piece at the center of the atom
Named it the Nucleus
Stated that Electrons moved around
Mostly empty space

35. Bohr’s Model
1913
Electrons travel around the nucleus in orbits of certain energies. Like planets around the sun
Amounts of energy separate one level from another.

36. Bohr’s Model
In order to move from the original or ground state to an excited state or higher energy level an electron must absorb an energy quantum.
and
Must emit an energy quantum to move back toward the nucleus.

37. } Bohr’s Model Fifth Fourth Increasing energy Third Second First
Further away from the nucleus means more (quanta) energy.
There is no “in between” energy
Energy Levels
Fifth
Fourth
Third
Increasing energy
Second
First
Nucleus

38. Bohr’s Model Nucleus Electron Orbit Energy Levels
The electron can absorb quanta to move from one level to other
Energy Levels

39. The Quantum Mechanical Model
Bohr’s model could not explain the behavior of atoms that have more than one electron.
Bohr’s model could not account for the repulsion force between moving electrons

40. The Quantum Mechanical Model
Energy is quantized and comes in chunks.
A quanta is the amount of energy needed to move from one energy level to another.
Since the energy of an atom is never “in between” there must be a quantum leap in energy.
Electrons have properties of both waves and particles.

41. Heisenberg Uncertainty Principle
We can never the know the exact location and velocity of an electron (particle) at the same time.
Since we need light to see. When light is used the particle absorbs it and jumps to another location!

42. The Quantum Mechanical Model
to present
Things that are very small behave differently from things big enough to see.
The quantum mechanical model is a mathematical solution
It is not like anything you can see.

43. The Quantum Mechanical Model
Has energy levels for electrons.
Orbits are not circular.
They are a region in space.
An electron cloud.
It can only tell us the probability of finding an electron a certain distance from the nucleus.

44. The Quantum Mechanical Model
A area where there is a chance of finding an electron. Is the electron cloud.
The cloud is broken down into four quantum numbers

45. Quantum Mechanical Model

46. Subatomic particles Relative mass Actual mass (g) Name Symbol Charge
Electron e- -1
9.11 x 10-28
Proton p+ +1 1
1.67 x 10-24
Neutron n0 1
1.67 x 10-24

47. Counting the Pieces Atomic Number = number of protons in the nucleus
# of protons determines the kind (name) of atom
# of protons is the same as the number of electrons in the neutral atom.

48. Counting the Pieces Mass Number = the number of Protons + Neutrons.
These account for most of mass

49. Nuclear Symbols
Contain the symbol of the element, the mass number and the atomic number.
Mass
number X
Atomic
number

50. F Symbols 19 9 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number 19 F 9

51. Br Symbols 80 35 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number 80 Br 35

52. Symbols
if an element has an atomic number of 34 and a mass number of 78 what is the
number of protons
number of neutrons
number of electrons
Nuclear symbol

53. Symbols if an element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
Nuclear symbol

54. Symbols if an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
Nuclear symbol

55. Isotopes Dalton was wrong.
Atoms of the same element can have different numbers of neutrons.
different mass numbers.
called isotopes.

56. Naming Isotopes
We can also put the mass number after the name of the element.
carbon- 12
carbon -14
uranium-235

57. Atomic Mass How heavy is an atom of oxygen?
There are different kinds of oxygen atoms.
More concerned with average atomic mass.
Based on abundance of each element in nature.
Don’t use grams because the numbers would be too small.

58. Measuring Atomic Mass Unit is the Atomic Mass Unit (amu)
One twelfth the mass of a carbon-12 atom.
Each isotope has its own atomic mass, thus we determine the average from percent abundance.

59. Calculating averages
Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.
Sample

60. Atomic Mass
Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and the rest has a mass of amu.

61. Atomic Mass
Magnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 25 with a mass of amu. What is the average atomic mass of magnesium? ____________
If not told otherwise, the mass of the isotope is the mass number in amu

62. Atomic Mass Is not a whole number because it is an average.
are the decimal numbers on the periodic table.

63. IONS
Ions - atoms or groups of bonded atoms that has a positive or negative charge
How does an atom get a positive or negative charge?

64. X IONS By losing or gaining electrons.
It is the electron that can move. X
Mass Number
Charge
Atomic
Number

65. IONS Li +1 F -1 19 7 3 9 Metals lose electrons.
Nonmetals gain electrons. 19 7
Li +1 F -1 3 9

66. IONS
If an element has 17 protons, 18 electrons, what is the charge on the ion? Write the symbol.
If an element has 20 protons, 18 electrons, what is the charge on the ion? Write the symbol.

67. SUMMARY Atomic Number is made up of ________________.
Atomic Mass is made up of
_______________ and _____________.
Isotopes have different
numbers of _____________________.

68. Summary Ions have different numbers of ___________________.
A positive ion ____________
electrons.
A negative ion ___________

69. Isotopes Revisited What is an isotope?
What subatomic particle is the same in isotopes?
What subatomic particle is different in isotopes?