1. 10/26/2015 Today I will discuss the early models of the atom.
Warm Up – What do you already know about atoms?

2. Chapter 3 – Atomic Structure
Chemistry

3. Early Models of the Atom
Atom – smallest part of an element that retains the chemical properties of that element.

4. Early Models of the Atom
Greek philosophers – around 400 BC
Democritus – “atomos”
Aristotle – Earth, Air, Fire, Water

5. Early Models of the Atom
Antoine Lavoisier – late 1700s
Law of Conservation of Matter – matter can be neither created nor destroyed.
Starting = Ending

6. Early Models of the Atom
Joseph Proust
Law of Definite Proportions – a given compound always contains the same elements in the same proportions by mass.
88.9% of mass is oxygen and 11.1% of mass is hydrogen

7. Early Models of the Atom
John Dalton – 1803
Dalton’s Atomic Theory
Each element is composed of extremely small, indivisible particles called atoms.
All atoms of a given element are the same, atoms of different elements are different.
Atoms are neither created nor destroyed.
A given compound always has the same relative numbers and kinds of atoms.
Democritus
Not always true!
Lavoisier
Proust

8. Early Model of the Atom
Notice it has been over 2000 years since Democritus first introduced the idea of the atom.
Science now relies on observations and experiments rather than just thoughts.

9. Early Models of the Atom
Dalton - “Billiard Ball” Model

10. Early Models of the Atom
Michael Faraday – 1839
Atom structure contain particles that have electrical charge.
Elektron
From Greek word for Amber
Describes static electricity (charges not in motion)
Benjamin Franklin
Called charges positive (+) and negative (-)

11. Early Models of the Atom
Why don’t we know for sure?
Different Worlds –
Macroscopic – ordinary-sized objects
Microscopic – seen through a microscope
Sub-microscopic – cannot be seen through a microscope (chemistry)

12. Early Models of the Atom
Scanning Tunneling Microscope

13. Cool Down Question
How has your idea of an atom changed since the beginning of class?

14. 10/27/15
Today I will discuss the early figures involved in modern atomic theory
Warm up – Discuss the events in early Greece that set science back thousands of years.

15. Atomic Structure J.J. Thomson – 1869
Cathode Ray Tube
Named negative particles “electrons”
Negatively charged plate
Positivelycharged plate

16. Atomic Structure J.J Thomson – 1869 Plum-pudding model
Charge to mass ratio
Coulomb (C) – SI unit of charge
1.76 x 108 Coulombs per gram

17. Atomic Structure Robert Millikan Oil Drop Experiment
Determined charge on an electron
1.60 x 10-19C (Coulomb – SI unit of charge)
Calculated mass using charge to mass ratio
9.11 x 10-28g

18. Nuclear Atom Ernest Rutherford – 1909 Gold foil Experiment
Alpha particle – large positive particle
Composed of two protons

19. Nuclear Atom Ernest Rutherford – 1909
Gold foil Experiment – If Thomson is correct:

20. Nuclear Atom Ernest Rutherford – 1909 Gold foil Experiment
Nucleus – small positive center of an atom that contains most of its mass

21. Nuclear Atom
Rutherford’s Model

22. Cool Down Question
How has your idea of the atom changed even further today?

23. 10/28/2015
Today I will explain protons, neutrons and electrons and determine the number of each in an atom.
Warm Up – What are protons, neutrons & electrons?
*Staple Lab reports and make a pile by the window!

24. Modern Atomic Theory Atoms are composed of:
Protons, neutrons, electrons
Particle
Location
Charge
Mass (g)
Rel
Mass
Rel Charge
proton
Inside nucleus
+1.6x10-19
1.673x10-24
neutron
1.675x10-24
electron
Outside nucleus
-1.6x10-19
9.109x10-28

25. Modern Atomic Theory Atomic Mass Units
1/12 the mass of a carbon-12 atom
(so basically the relative mass of a proton or neutron)

26. Modern Atomic Theory (Protons)
Moseley - An element is defined by the number of protons in it’s atoms.
Atomic Number - # of protons in an atom
How many protons are in each atom of nitrogen?

27. Modern Atomic Theory (Protons)
How many protons?
Copper
Sodium
Helium

28. Modern Atomic Theory (Electrons)
In an electrically neutral atoms, the number of electrons must equal the number of protons.
How many electrons are in each atom of nitrogen?

29. Modern Atomic Theory (Electrons)
How many electrons?
Copper
Sodium
Helium

30. Modern Atomic Theory (Electrons)
Ions
An atom that has an electrical charge due to gaining or losing electrons
Gaining electrons makes the atom negative overall (more negatives than positives)
Losing electrons make the atom positive overall (more positives)

32. Modern Atomic Theory (Electrons)
Ions
An atom that has an electrical charge due to gaining or losing electrons
How many electrons in a chlorine atom that has a -1 charge?

33. Modern Atomic Theory (Electrons)
How many electrons?
Copper (+2)
Sodium (-1)
Helium (+2)

34. Modern Atomic Theory (Electrons)
Finding Charge
Remember:
More electrons makes overall negative
More protons makes overall positive
Find the charge & write the symbol:
34 protons, 36 electrons
13 protons, 10 electrons

35. 10/29/15
Today I will explain isotope and count the number of neutrons in an atom.
Warm up – How many protons and electrons in an atom of sulfur with a -2 charge?

36. Modern Atomic Theory (Neutrons)
Neutrons add stability to a nucleus
Only the protons and the neutrons have mass (for practical purposes).
Protons + Neutrons = Mass Number
What is the mass number of chlorine if it has 18 neutrons?

37. Modern Atomic Theory (Neutrons)
Isotopes
An atom that has the same number of protons but different numbers of neutrons
Same protons, means it’s the same element
Different neutrons changes the mass!

38. Modern Atomic Theory (Neutrons)
Mass number = protons + neutrons
How many neutrons does Cl have if its mass number is 36?

39. Modern Atomic Theory Mass Number Notation Symbolic Notation
Name-mass number
Symbolic Notation
Mass number 
 Charge
Atomic number 

40. Cool Down Question How many protons, neutrons and electrons? 53 55 54
Protons Neutrons Electrons 53 55 54 12 13 10 8 10 8

41. 10/30/15
Today I will practice finding the number of protons, neutrons and electrons in atoms, ion sand isotopes.
Warm Up –
How many protons neutrons and electrons in
Bromine – 74
Sodium - 24

42. 11/2/15 Objective – to calculate average atomic mass Warm Up –
How many protons neutrons and electrons in
Oxygen – 18
Lithium-8

43. Atomic Mass
Atomic Mass – The average mass of all the isotopes of an atom Shown below the symbol on the periodic table.

44. Modern Atomic Theory You get the following grades:
A,A,A,A,C,A,A,A,A,A.
Can we average the A’s and the C’s to get a B average?
No! We have to take into account the percent of your grade that are A’s and the percent that are C’s
You could do:
/10 = 3.8

45. Modern Atomic Theory You get the following grades:
A,A,A,A,C,A,A,A,A,A.
You could also find your average grade by Percent Abundance!
You have 90% A’s and 10% C’s.
So…
(.9)(4) = 3.6
(.1)(2) = 0.2
3.8

46. Modern Atomic Theory Average Atomic Mass
The average mass of an atom would be the mass of all the atoms in the world averaged.
Can we count up the masses of all the atoms and divide by the number?
Percent Abundance! – we can calculate average atomic mass based on the known percents of each isotope.

47. Modern Atomic Theory
What is the average atomic mass of Nitrogen? Fractional abundance – percent abundance as a decimal
mass number
exact mass
percent abundance 14
14.003
99.63 15
15.000
0.37
mass number
exact mass
Fractional abundance 14
14.003
0.9963 15
15.000
0.0037

48. Modern Atomic Theory
AAM = (mass)(fractional abundance) + (mass)(fractional abundance) + …
What is the average atomic mass of Nitrogen?
mass number
exact mass
percent abundance 14
14.003
99.63 15
15.000
0.37
(14.003)
(0.9963) +
(15.000)
(0.0037) =
(14.007)
Average Atomic Mass of Nitrogen is amu.

49. Cool Down Question What element is represented below? (27.977)
Mass number
Exact mass
Percent abundance 28
27.977
92.23 29
28.976
4.67 30
29.973
3.10
(27.977)
(0.9223) +
(28.976)
(0.0467) +
(29.973)
(0.0310) =
(28.086)
Average Atomic Mass is amu.
From periodic table, it must be silicon!

50. 11/4/15 Today I will write nuclear equations
Warm up – Calculate the average atomic mass for Magnesium:
mass number
exact mass
percent abundance 24
23.985
78.99 25
24.985
10.00 26
25.982
11.01

51. Early Models of the Atom
Henri Bequerel
Uranium exhibits radioactivity
Radioactivity changes the properties of an atom.

52. Changes in the Nucleus
If all atoms of the same element have the same properties, how can they change?
Nuclear reactions – radioactive changes that alter the composition of the nucleus.
Therefore, they change their identity!

53. Changes in the Nucleus
How can these positive protons live together if like charges repel?
Strong Nuclear Force – attractive force that overcomes the repulsion of the protons.
Neutrons help stabilize! - The larger the nucleus, the greater the neutron to proton ratio.

54. Changes in the Nucleus
At some point, there can be too much repulsion to overcome & nucleus becomes unstable.
All elements above atomic number 83 are unstable or radioactive!
Some isotopes of smaller elements can be radioactive too if they have too many neutrons!

55. Changes in the Nucleus
Radioactive decay – spontaneous emission of radioactive particles from the nucleus.
Radioactive Particles:
Alpha – 2 protons & 2 neutrons
Beta – electron from the nucleus (1 neutron becomes 1 electron and 1 proton)
Gamma – energetic form of light

56. Medium, stopped by heavy clothing
Changes in the Nucleus
Radioactive Particles:
Particle
Symbol
Equation symbol
Charge
Penetrating ability
Energy
Danger
alpha α +2
Low, stopped by paper
Low
beta β -1
Medium, stopped by heavy clothing
Medium
gamma ɣ
none
High, stopped by lead
High

57. Changes in the Nucleus
Alpha Decay – emission of an alpha particle +

58. Changes in the Nucleus
Beta Decay – emission of a beta particle +

59. Cool Down Question
Write the nuclear equation for the beta decay of Bismuth-209

60. 11/5/15 Today I will demonstrate the idea of average atomic mass.
Warm Up – Why do we use an average of atomic mass rather than the actual mass?

61. Pennium Lab What is an isotope?
Pretend each penny is an atom. How can we tell if there are different isotopes in our sample of Pennium?

62. 11/6/15 Objective – to review chapter 3
Warm up – Calculate the average atomic mass for Magnesium:
mass number
exact mass
percent abundance 24
23.985
78.99 25
24.985
10.00 26
25.982
11.01

63. 11/9/15 Warm Up – How many protons, neutrons and electrons:
Objective –to review for the chapter 3 exam
Warm Up –
How many protons, neutrons and electrons:
A. selenium – 70
B. curium - 244
Write the equations for the following:
A. The beta decay of selenium- 70
B. The alpha decay of curium - 244

64. How many protons, neutrons and electrons:
A. selenium – 70
P = 34 N = 36 E = 34
B. curium - 244
P = 96 N = 148 E = 96
Write the equations for the following:
A. The beta decay of selenium- 70
B. The alpha decay of curium - 244

65. Symbolic Form
Mass Form
Atomic #
Mass #
Protons
Neutron
Electron
Atomic Mass
Iron - 56 13 14 10