10/26/2015 4.3 Modern Atomic Theory 1 4.3 MODERN ATOMIC THEORY VOCABULARY: energy levels electron cloud orbital OBJECTIVES: Describe Bohr ’

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

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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

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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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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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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

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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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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).

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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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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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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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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

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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.

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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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ELECTRON CLOUD MODEL

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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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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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ELECTRON CONFIGURATION

David’s Wizzy Periodic Table - Click on Element to See Atom Structure

http://www.colorado.edu/physics/2000/applets/a2.html

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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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FLAME TEST

To prepare for tomorrow’s lab you have to read section 4.3 and the lab handout.

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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

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