1. Atomic Theory Observation vs. Inference Square = Model/Theory Activity
Black Boxes
Hypotheses & Theory
History of Atomic Structure
Explain to a classmate and to one other outside of class. Must Initial.
Notes not used with outside person.
Ch 4 in Physcial Science

2. Ancient…Greek philosopher Democritus – “Atoms”
Greek word atomos, which means “uncut” or “indivisible.”
Aristotle did not think there was a limit to the division of matter.

3. Dalton (1803)
all matter is made up of individual particles called atoms, which cannot be divided.
Dalton measured masses of elements that combine when compounds form. The ratio of the masses of the elements in each compound was always the same. In other words, compounds have a fixed composition.
Dalton’s Theory
All elements are composed of atoms.
All atoms of the same element have the same mass, and atoms of different elements have different masses.
Compounds contain atoms of more than one element.
In a particular compound, atoms of different elements always combine in the same way

4. Thomson (1904)
Observation

5. Thomson (1904) Thomson’s Experiments
In his experiments, Joseph John Thomson used a sealed tube containing a very small amount of gas.

6. Thomson (1904) Thomson’s Experiments
In his experiments, Joseph John Thomson used a sealed tube containing a very small amount of gas.

7. Evidence for Subatomic Particles
Thomson hypothesized that the beam was a stream of charged particles that interacted with the air in the tube and caused the air to glow.
Thomson observed that the beam was repelled by the negatively charged plate and attracted by the positively charged plate.
the particles had about 1/2000 the mass of a hydrogen atom, the lightest atom.

8. Thomson revised Dalton’s model to account for these subatomic particles.
“plum pudding” model

9. Rutherford’s Atomic Theory
The Gold Foil Experiment
Alpha particles
Undeflected particle
Deflected particle
Gold atoms
Slit
Beam of alpha particles
Alpha particles
Screen
Source of alpha particles
Nucleus

10. Discovery of the Nucleus
Thomson’s model did not explain all of the evidence from Rutherford's experiment. Rutherford proposed a new model.
The nucleus of the atom is a dense, positively charged mass located in the center of the atom.

13. Dalton’s theory did not include which of the following points?
Assessment Questions
Dalton’s theory did not include which of the following points?
All elements are composed of atoms.
Most of an atom’s mass is in its nucleus.
Compounds contain atoms of more than one element.
In a specific compound, atoms of different elements always combine in the same way.

14. Dalton’s theory did not include which of the following points?
Assessment Questions
Dalton’s theory did not include which of the following points?
All elements are composed of atoms.
Most of an atom’s mass is in its nucleus.
Compounds contain atoms of more than one element.
In a specific compound, atoms of different elements always combine in the same way. ANS: B

15. J. J. Thomson’s experiments provided the first evidence of
Assessment Questions
J. J. Thomson’s experiments provided the first evidence of
atoms.
a nucleus.
subatomic particles.
elements.

16. J. J. Thomson’s experiments provided the first evidence of
Assessment Questions
J. J. Thomson’s experiments provided the first evidence of
atoms.
a nucleus.
subatomic particles.
elements. ANS: C

17. Assessment Questions
The concept of an atom as a small particle of matter that cannot be divided was proposed by the ancient Greek philosopher, Democritus. True False

18. Assessment Questions
The concept of an atom as a small particle of matter that cannot be divided was proposed by the ancient Greek philosopher, Democritus. True False
ANS: T

19. Atomic Theory Flip Book
Purpose:  Create a flip-book to show how the Atomic Theory has changed over time.  Worth 35 points.
Your flip-book must have the following:
Title page (creatively done)
One page for each of the following 7 names
Democritus
Aristotle
Dalton
Thomson
Rutherford
Bohr
Schrodinger & Heisenberg
Each page needs to have the following information: (4 pts for each scientist, 1pt if colored)
Full name(s)
Approximate time in history
Major points of contribution to the understanding of the atom and a brief description of experiments (if any)
Sketch or diagram of the scientists atomic model
One additional interesting fact about the person or model
How to Make a Flip-Book
Stack 4 sheets of paper, and place each sheet one higher than the previous sheet in the stack.
Bring the bottom of all 4 sheets upward and align the edges so that all of the layers are the same distance apart.
When all the tabs are an equal distance apart, fold the papers and crease well.
Open the papers and glue them together all the center fold.

20. Protons, electrons, and neutrons can be distinguished by mass, charge, and location in an atom.

21. Atomic Structure No tool to “see” inside an atom Indirect observations
Relative Mass Unit  Atomic Mass Unit (AMU) P=1 N=1 e=0

25. Practice
The atomic number of aluminum is 13. An atom of aluminum that has a mass number of 27 has 13 protons and 14 neutrons

26. More Practice
How many P+? E-? N0?

29. Bean Bag Isotopes….Activity

30. Hydrogen is an exception...
Isotopes
With most elements, it is hard to notice any differences in the physical or chemical properties of their isotopes.
Hydrogen is an exception...
Hydrogen-1 has no neutrons. (Almost all hydrogen is hydrogen-1.)
Hydrogen-2 has one neutron
Hydrogen-3 has two neutrons.
..Because a hydrogen-1 atom has only one proton, adding a neutron doubles its mass.

31. Isotopes
Water that contains hydrogen-2 atoms in place of hydrogen-1 atoms is called heavy water. Hydrogen-2 atoms have twice the mass of hydrogen-1 atoms, so the properties of heavy water are different from the properties of ordinary water.

32. In which way do isotopes of an element differ?
Assessment Questions
In which way do isotopes of an element differ?
number of electrons in the atom
number of protons in the atom
number of neutrons in the atom
net charge of the atom

33. In which way do isotopes of an element differ?
Assessment Questions
In which way do isotopes of an element differ?
number of electrons in the atom
number of protons in the atom
number of neutrons in the atom
net charge of the atom ANS: C

34. Assessment Questions
Of the three subatomic particles that form the atom, the one with the smallest mass is the neutron. True False

35. Assessment Questions
Of the three subatomic particles that form the atom, the one with the smallest mass is the neutron. True False
ANS: F, electron

39. 4.3

40. Bohr’s Model of the Atom
What can happen to electrons when atoms gain or lose energy?

41. Bohr’s Model of the Atom
Bohr’s model focused on the electrons and their arrangement.
In Bohr’s model, electrons move with constant speed in fixed orbits around the nucleus, like planets around a sun.
Each electron in an atom has a specific amount of energy.

42. Bohr’s Model of the Atom
Energy Levels
When an atom gains or loses energy, the energy of an electron can change.
The possible energies that electrons in an atom can have are called energy levels.
An electron cannot exist between energy levels.

43. Bohr’s Model of the Atom
An electron in an atom can move from one energy level to another when the atom gains or loses energy.
Electron
Electrons gain or lose energy when they move between fixed energy levels
Nucleus
Bohr Model

44. Bohr’s Model of the Atom
An analogy for energy levels of electrons is a staircase.
The landing at the bottom of the staircase is the lowest level.
Each step up represents a higher energy level.
The step height represents an energy difference between levels.
You can only move in whole numbers of stairs.

45. Bohr’s Model of the Atom
An electron may move up or down two or more energy levels if it gains or loses the right amount of energy.
The size of the jump between energy levels determines the amount of energy gained or lost.
No two elements have the same set of energy levels.

46. Bohr’s Model of the Atom
Evidence for Energy Levels
Scientists can measure the energy gained when electrons absorb energy and move to a higher energy level or measure the energy released when the electron moves to a lower energy level.
Light is a form of energy that can be observed.

47. Electron Cloud Model
What model do scientists use to describe how electrons behave in atoms?
An electron cloud is a visual model of the most likely locations for electrons in an atom.
Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus.

48. Bohr’s  Electron Cloud Model
Today, scientists use probability when trying to predict the locations and motions of electrons in atoms.
An electron cloud is a visual model of the most likely locations for electrons in an atom.

49. Electron Cloud Model
The electron cloud model replaced Bohr's vision of electrons moving in predictable paths.
The nucleus contains protons and neutrons
electrons
Electron Cloud Model

50. Electron Cloud Model

51. Electron Cloud Model
What model do scientists use to describe how electrons behave in atoms?
An orbital is a region of space around the nucleus where an electron is likely to be found.
The electron cloud represents all the orbitals in an atom.
An electron cloud is a good approximation of how electrons behave in their orbitals.

52. 1 dot every 10 minutes between 0730 and 1400
Electron Cloud Model
For an analogy to the concept of an orbital, imagine a map of your school:
1 dot every 10 minutes between 0730 and 1400
Mark your exact location with a dot once every 10 minutes over a period of one week.
The dots on your map are a model of your “orbital.” They describe your most likely locations.
The places you visit the most would have the highest concentration of dots.
The places you visit the least would have the lowest concentration of dots.

53. Electron Cloud Model
The level in which an electron has the least energy—the lowest energy level—has only one orbital. Higher energy levels have more than one orbital.

55. Electron Configurations
The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies.
The ground state of a person is on the floor. A gymnast on a balance beam is like an atom in an excited state—not very stable.
When she dismounts, the gymnast will return to a lower, more stable energy level.

56. Assessment Questions
According to Bohr’s model of the atom, which of the following can happen when an atom gains energy?
An atom returns to its ground state.
A neutron can be changed into a proton.
A proton can move to a higher energy level.
An electron can move to a higher energy level.

57. Assessment Questions
According to Bohr’s model of the atom, which of the following can happen when an atom gains energy?
An atom returns to its ground state.
A neutron can be changed into a proton.
A proton can move to a higher energy level.
An electron can move to a higher energy level. ANS: D

58. Assessment Questions
How does the modern atomic theory describe the location of electrons in an atom?
Electrons move randomly in space around the nucleus.
Electrons can be described as a cloud based on probable locations.
Electrons orbit the nucleus in the same way that planets orbit the sun.
Electrons move in a spiral pattern if increasing distance from the nucleus.

59. Assessment Questions
How does the modern atomic theory describe the location of electrons in an atom?
Electrons move randomly in space around the nucleus.
Electrons can be described as a cloud based on probable locations.
Electrons orbit the nucleus in the same way that planets orbit the sun.
Electrons move in a spiral pattern if increasing distance from the nucleus. ANS: B

60. What is meant when an atom is said to be in its ground state?
Assessment Questions
What is meant when an atom is said to be in its ground state?
There is no net charge on the atom.
The number of protons equals the number of neutrons.
The atom’s electrons all have the lowest possible energies.
It is the isotope with the least number of neutrons.

61. What is meant when an atom is said to be in its ground state?
Assessment Questions
What is meant when an atom is said to be in its ground state?
There is no net charge on the atom.
The number of protons equals the number of neutrons.
The atom’s electrons all have the lowest possible energies.
It is the isotope with the least number of neutrons. ANS: C