10/26/2015 4.3 modern atomic theory 1 4.3 modern atomic theory vocabulary: energy levels electron...
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04/20/23 4.3 Modern Atomic Theory 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
04/20/23 4.3 Modern Atomic Theory 2
BOHR’S MODEL OF THE ATOM
Niels Bohr (1885 -1962) 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
04/20/23 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).
04/20/23 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).
04/20/23 4.3 Modern Atomic Theory 5
BOHR’S MODEL OF THE ATOM
Atomic structure animation table for first 11 elements of the Periodic Table
http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-animations.shtml
04/20/23 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.
04/20/23 4.3 Modern Atomic Theory 7
BOHR’S MODEL OF THE ATOM: ENERGY LEVELS http://www.colorado.edu/physics/2000/quantumzone/bohr.
html
Larger orbit to smaller orbit – loses energy (squiggle shoots out)
Smaller orbit to larger orbit – gains energy (squiggle comes in).
04/20/23 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.
04/20/23 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.
04/20/23 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.
04/20/23 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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ELECTRON CLOUD MODEL
04/20/23 4.3 Modern Atomic Theory 13
ELECTRON CLOUD MODEL
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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.
04/20/23 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.
04/20/23 4.3 Modern Atomic Theory 16
ELECTRON CLOUD MODEL
04/20/23 4.3 Modern Atomic Theory 17
ELECTRON CONFIGURATION
Configuration is an arrangement of objects in a given space.
Some configurations more stable than others (less likely to change)
04/20/23 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
04/20/23 4.3 Modern Atomic Theory 19
ELECTRON CONFIGURATION
David’s Wizzy Periodic Table - Click on Element to See Atom Structure
http://www.colorado.edu/physics/2000/applets/a2.html
04/20/23 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.
04/20/23 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.
04/20/23 4.3 Modern Atomic Theory 22
Bohr’s Atom http://www.visionlearning.com/library/flash_viewer.php?oid=1347
periodic table 11 elements http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-atoms.shtml
http://www.visionlearning.com/library/index.php
http://www.visionlearning.com/library/module_viewer.php?mid=51&l=&c3=
common isotopes http://web.visionlearning.com/custom/chemistry/overheads/CHE1.3-oh-
isotopes.shtml
Brainpop.com