1. 4.3 MODERN ATOMIC THEORY VOCABULARY: energy levels electron cloud
orbital
OBJECTIVES:
Describe Bohr’s model of the atom and the evidence for energy levels.
Explain how the electron cloud model represents the behavior and locations of electrons in atoms.
VOCABULARY:
electron configuration
ground state
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4.3 Modern Atomic Theory

2. BOHR’S MODEL OF THE ATOM
Niels Bohr ( )
Danish physicist
Worked with Rutherford
Agreed with Rutherford’s model
of a nucleus surrounded by large
volume of space. However, Bohr’s
model focused on electrons.
Main focus of modern atomic model: describing the arrangement of electrons in an atom
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4.3 Modern Atomic Theory

3. BOHR’S MODEL OF THE ATOM
In Bohr’s model, electrons move w/ constant speed in fixed orbits around nucleus.
Looks like solar system with planets (electrons) revolving (orbiting) around sun (nucleus).
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4.3 Modern Atomic Theory

4. BOHR’S MODEL OF THE ATOM
In Bohr’s model, electrons move w/ constant speed in fixed orbits around nucleus.
Looks like solar system with planets (electrons) revolving (orbiting) around sun (nucleus).
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4.3 Modern Atomic Theory

5. BOHR’S MODEL OF THE ATOM
Atomic structure animation table for first 11 elements of the Periodic Table
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4.3 Modern Atomic Theory

6. BOHR’S MODEL OF THE ATOM: ENERGY LEVELS
Each electron has a specific amount of energy.
Energy levels - possible energies that electrons in an atom can have
An electron in an atom can move from one energy level to another when the atom gains or loses energy.
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4.3 Modern Atomic Theory

7. BOHR’S MODEL OF THE ATOM: ENERGY LEVELS
Larger orbit to smaller orbit – loses energy (squiggle shoots out)
Smaller orbit to larger orbit – gains energy (squiggle comes in).
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4.3 Modern Atomic Theory

8. BOHR’S MODEL OF THE ATOM: EVIDENCE FOR ENERGY LEVELS
Scientist can measure…
energy gained when
electrons absorb energy
& move to a higher
energy level.
energy released when
electron returns to a
lower energy level.
Light is usually emitted when electrons move to lower energy levels.
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4.3 Modern Atomic Theory

9. ELECTRON CLOUD MODEL
As scientist made more discoveries, Bohr’s model was improved.
Bohr’s model
correct in introducing concept of energy levels
incorrect in assuming electrons moved like planets do in our solar system
Can’t be sure at a specific moment where electrons are located because electrons move in less predictable ways & energy levels cannot be used to describe actual location of an electron.
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4.3 Modern Atomic Theory

10. ELECTRON CLOUD MODEL
Electron cloud - visual model of the most likely locations for electrons in an atom.
cloud is denser at locations where probability of finding an electron is high
Scientist use the electron cloud model to describe the possible locations of electrons around the nucleus.
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4.3 Modern Atomic Theory

11. ELECTRON CLOUD MODEL Example: propeller moving
know blades are located somewhere in blur but you can’t be exactly sure where each blade is located at specific moment in time.
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4.3 Modern Atomic Theory

12. ELECTRON CLOUD MODEL
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13. ELECTRON CLOUD MODEL
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14. ATOMIC ORBITALS Electron cloud represents all the orbitals in an atom.
Orbital - region of space around nucleus where an electron is likely to be found
An electron cloud is a good approximation of how electrons behave in their orbitals.
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4.3 Modern Atomic Theory

15. ATOMIC ORBITALS Lowest energy level (least energy) has 1 orbital
Highest energy level has more than one orbital
Max number of
electrons in an energy
level is twice #
of orbitals
Each orbital can
contain two
electrons at most.
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4.3 Modern Atomic Theory

16. ELECTRON CLOUD MODEL
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17. ELECTRON CONFIGURATION
Configuration is an arrangement of objects in a given space.
Some configurations more stable than others (less likely to change)
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4.3 Modern Atomic Theory

18. ELECTRON CONFIGURATION
Electron configuration - arrangement of electrons in the orbitals of an atom
The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies.
Ground state - all electrons in an atom have the lowest possible energies
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4.3 Modern Atomic Theory

19. ELECTRON CONFIGURATION
David’s Wizzy Periodic Table - Click on Element to See Atom Structure
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4.3 Modern Atomic Theory

20. SUMMARY
In the past , scientist believed that electrons circled the nucleus the same way the planets circled the sun. Today however, scientists know that there is no exact path of an electron. The quick moving electrons form a “cloud” around the nucleus.
In the modern atomic theory, electrons are arranged into energy levels, or shells.
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4.3 Modern Atomic Theory

21. FLAME TEST
To prepare for tomorrow’s lab you have to read section 4.3 and the lab handout.
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22. periodic table 11 elements
Bohr’s Atom
periodic table 11 elements
common isotopes
Brainpop.com
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