1. Today’s special HW check – Vocab 4 Test results NASA update
Where did all these planets come from?
Notes 4 Atoms & their electrons
HW I due next

2. 4 Atomic models
PAb.1: Compare the subatomic particles (protons, neutrons, electrons) of an atom with regard to mass, location, and charge, and explain how these particles affect the properties of an atom (including identity, mass, volume, and reactivity).
PAb.3: Explain the trends of the periodic table based on the elements’ valence electrons and atomic numbers.
PAb.5: Predict the charge that a representative element will acquire according to the arrangement of electrons in its outer energy level.
PAa.2: Use appropriate laboratory apparatuses, technology, and techniques safely and accurately when conducting a scientific investigation.
PAa.9: Use appropriate safety procedures when conducting investigations.

3. Never trouble another for what you can do for yourself.
Thomas Jefferson
Fact: Boston built the first subway system in the United States in 1897.

4. Ancient Greek Models of Atoms
The philosopher Democritus believed that all matter consisted of extremely small particles that could not be divided. He called these particles atoms from the Greek word atomos, which means “uncut” or “indivisible.”

5. Ancient Greek Models of Atoms
Aristotle thought that all substances were made of only four elements—earth, air, fire, and water. He did not think there was a limit to the division of matter.
For many centuries, most people accepted Aristotle’s views on the structure of matter. By the 1800s, scientists had enough experimental data to support an atomic model.

6. Dalton’s Atomic Theory
What was Dalton’s theory of the structure of matter?
Dalton proposed the theory that all matter is made up of individual particles called atoms, which cannot be divided.

7. Dalton’s Atomic Theory
When magnesium burns, it combines with oxygen. In magnesium oxide, the ratio of the mass of magnesium to the mass of oxygen is always about 3 : 2. Magnesium dioxide has a fixed composition.

8. Dalton’s Atomic 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.

9. Thomson’s Model of the Atom
What contributions did Thomson make to the development of atomic theory?
Thomson’s experiments provided the first evidence that atoms are made of even smaller particles.

10. Thomson’s Model of the Atom
Amber is the hardened form of a sticky, viscous liquid that protects trees from insects and disease. If amber is rubbed with wool, it becomes charged and can attract a feather.

11. Thomson’s Model of the Atom
Thomson’s Experiments
In his experiments, Joseph John Thomson used a sealed tube containing a very small amount of gas.
Sealed tube filled with gas at low pressure
Glowing beam
Positive plate
Metal disk
Negative plate
Metal disk
Metal disk
Source of electric current
Source of electric current

12. Thomson’s Model of the Atom
Thomson revised Dalton’s model to account for these subatomic particles.
The atom has neither a positive nor a negative charge, but there must always be some positive charge in the atom.
The atom is filled with a positively charged mass of matter that has negative charges evenly scattered throughout it.

13. Thomson’s Model of the Atom
Thomson’s model is called the “plum pudding” model. Today, it might be called the “chocolate chip ice cream” model.
The chips represent negatively charged particles, which are spread evenly through a mass of positively charged matter—the vanilla ice cream.

14. Rutherford’s Atomic Theory
What contributions did Rutherford make to the development of atomic theory?
According to Rutherford’s model, all of an atom’s positive charge is concentrated in its nucleus.

15. 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

16. Rutherford’s Atomic Theory
The Houston Astrodome occupies more than nine acres and seats 60,000 people. If the stadium were a model for an atom, a marble could represent its nucleus.
The total volume of an atom is about a trillion (1012) times the volume of its nucleus.

17. 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.

18. 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

19. 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.

20. 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

21. 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

22. 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

23. Models
Physical model – is a “real” representation of a very large or very small object on a convenient scale
i.e. the solar system, cells, a globe

24. Models
Conceptual model – explains behavior of a system, the interaction between the components; its criteria is how well it explains behavior, not how it matches true physical form

25. Properties of Subatomic Particles
What are three subatomic particles?
Protons, electrons, and neutrons are subatomic particles.

26. Properties of Subatomic Particles
Protons
Based on experiments with elements other than gold, Rutherford concluded that the amount of positive charge varies among elements.
A proton is a positively charged subatomic particle that is found in the nucleus of an atom. Each proton is assigned a charge of 1+. Each nucleus must contain at least one proton.

27. Properties of Subatomic Particles
Electrons
The particles that Thomson detected were later named electrons.
An electron is a negatively charged subatomic particle that is found in the space outside the nucleus. Each electron has a charge of 1.

28. Properties of Subatomic Particles
Neutrons
In 1932, the English physicist James Chadwick carried out an experiment to show that neutrons exist. Chadwick concluded that the particles he produced were neutral because a charged object did not deflect their paths.
A neutron is a neutral subatomic particle that is found in the nucleus of an atom. It has a mass almost exactly equal to that of a proton.

29. Comparing Subatomic Particles
What properties can be used to compare protons, electrons, and neutrons?
Protons, electrons, and neutrons can be distinguished by mass, charge, and location in an atom.

30. Comparing Subatomic Particles
Everything scientists know about subatomic particles is based on how the particles behave in experiments. Scientists still do not have an instrument that can show the inside of an atom.

31. Atomic Number and Mass Number
How are atoms of one element different from atoms of other elements?
Atoms of different elements have different numbers of protons.

32. Atomic Number and Mass Number
Each element has a different atomic number. A The atomic number of sulfur (S) is 16. B The atomic number of iron (Fe) is 26. C The atomic number of silver (Ag) is 47.

33. Atomic Number and Mass Number
The mass number of an atom is the sum of the protons and neutrons in the nucleus of that atom. To find the number of neutrons in an atom, you need the mass number of the atom and its atomic number.
The atomic number of aluminum is 13. An atom of aluminum that has a mass number of 27 has 13 protons and 14 neutrons

34. Isotopes
What is the difference between two isotopes of the same element?
Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.

35. 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.

36. 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

37. 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

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

39. 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

40. Today’s special A message from NASA for Cosmos STM (next slide)
HW check; Q & A
Lab: Atomic Structure
Lab due next time

41. Scanning tunneling microscope
Video

42. Today’s special Turn in lab on front table A boy and his atom Notes II
HW II due next time
Project: Adopt an element; due on test day!
What is an MSDS?

43. Have you ever wondered what produces the different colors in a fireworks display?
Certain compounds will produce certain colors of light when they are heated. Compounds containing the element strontium produce red light. Compounds containing barium produce green light.

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

45. Bohr’s Model of the Atom
As did Rutherford's atomic model, Bohr’s atomic model had a nucleus surrounded by a large volume of space. But 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.

46. 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.

47. 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

48. 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.

49. 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.

50. 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.

51. Bohr’s Model of the Atom
The movement of electrons between energy levels explains the light you see when fireworks explode.
Heat causes some electrons to move to higher energy levels.
When those electrons move back to lower energy levels, they release energy. Some of that energy is released as visible light.
Different elements emit different colors of light because no two elements have the same set of energy levels.

52. 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.

53. Electron Cloud Model
Bohr’s model was improved as scientists made further discoveries. Bohr correctly assigned energy levels to electrons, but electrons do not move like planets in a solar system.
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.

54. Electron Cloud Model
The electron cloud model replaced Bohr's vision of electrons moving in predictable paths.
The electron cloud is a visual model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud.
The nucleus contains protons and neutrons
Electron Cloud Model

55. Electron Cloud Model
This photograph provides an analogy for an electron cloud. When the blades of a windmill are at rest, you can count the number of blades. When the blades are moving, they spin so fast that you see only a blur. You know that the blades are located somewhere in the blur, but at any specific moment in time you can’t be exactly sure where each blade is located.

56. 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.

57. Electron Cloud Model
For an analogy to the concept of an orbital, imagine a map of your school. 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.

58. 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.

59. Electron Configurations
What is the most stable configuration of electrons in an atom?

60. Electron Configurations
An electron configuration is the arrangement of electrons in the orbitals of an atom.
When all the electrons in an atom have the lowest possible energies, the atom is said to be in its ground state.

61. Electron Configurations
The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies.

62. Electron Configurations
A lithium atom has three electrons.
In the ground state, two of the lithium electrons are in the orbital of the first energy level.
The third electron is in an orbital of the second energy level.
If a lithium atom absorbs enough energy, one of its electrons can move to an orbital with a higher energy.
This configuration is referred to as an excited state. An excited state is less stable than the ground state.
Eventually, the electron that was promoted to a higher energy level loses energy, and the atom returns to the ground state.

63. Valence electrons
Outer shell electrons are responsible for chemical reactions

64. Valence electrons
Lewis Dot Structures

65. Electron dot structures
Electron dot models help us explain chemistry
We will study the interactions of these outer shell electrons

66. Question
How do fluorescent lights work?

67. Today’s special HW check; Q & A Some more notes Notes again
Valance electrons activity (due next time)
Elemental mini-project (due on Review day)
Modern physics

68. 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.

69. 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

70. 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.

71. 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

72. 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.

73. 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

75. Today’s special HW check; Q & A Practice Test
Present project: Introduce your adopted element & tell us three interesting facts about it
Test next time!

76. Today’s special Turn in practice test on front desk
Test 18: Enter MC in Smart Response…write sentences and essay and turn in on front table.
Pick up Vocab 19 Radioactivity (due next!)
Shakespeare…the class!