4.3 Modern Atomic Theory
_________’s Model of the Atom
• Nucleus surrounded by large volume of _________
–focused on _______________
–constant speed
–fixed ____________
• Each electron has a specific amount of __________
4.3 Modern Atomic Theory
Bohr’s Model of the Atom
Energy Levels
• Possible energies of electrons
• An electron cannot exist_______________energy levels.
• Size of jump between energy levels determines
amount of____________gained or lost.
• No two elements have the same set of __________.
4.3 Modern Atomic Theory
Bohr’s Model of the Atom
An electron 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
4.3 Modern Atomic Theory
Bohr’s Model of the Atom
Analogy: staircase
• The landing at the bottom 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.
4.3 Modern Atomic Theory
Bohr’s Model of the Atom
Evidence for Energy Levels
• Scientists can measure the energy _________________
• _________: form of energy that can be observed.
• Example- Fireworks:
• Heat  Some electrons move to higher energy levels
• Electrons move back to lower energy levels and release
energy
• visible light
• Different colors: no elements have the same energy levels
4.3 Modern Atomic Theory
Electron Cloud Model
• Electrons do not move like ____________
• _________used to establish estimated electron location:
- Model
- Most likely locations for electrons
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
4.3 Modern Atomic Theory
Electron Cloud Model
Analogy: airplane propellers
• Propeller at rest: you can see the location of the blades.
• Propeller is moving: you see only a blur (“electron cloud”)
4.3 Modern Atomic Theory
Electron Cloud Model
Analogy: your path through the day
• Imagine a map of your school. Mark your exact location
with a dot once every 10 minutes over one week.
• The dots on your map are a model of your “orbital.”
• They describe your most likely locations.
4.3 Modern Atomic Theory
Electron Cloud Model
• Lowest energy level: has only one orbital
• Higher energy levels: have more than one orbital
4.3 Modern Atomic Theory
Electron Configurations
• Electron configuration: ________________of electrons
• _________state: all electrons have lowest possible energies
• _______state: electrons move to an orbital with higher energy
4.3 Modern Atomic Theory
Electron Configurations
Example: A lithium atom has three electrons.
• Ground state: two electrons are in the orbital of the first
energy level, third electron is in an orbital of the second
energy level.
• Absorbs enough energy  one of its electrons can
move to an orbital with a higher energy: excited state
• Less_______________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.
4.3 Modern Atomic Theory
Electron Configurations
• Analogy: Gymnast
• The ground state of a person is on
the floor.
• A gymnast on a balance beam is
like an atom in an excited state
• When she dismounts, the
gymnast will return to a lower, more
stable energy level.
4.3 Modern Atomic Theory
1. What did Bohr focus his model on?
2. What do we use to determine the likely locations of
electrons in the electron cloud model?
3. If all electrons are in the lowest possible energy levels,
what state is the atom in?
4. If electrons move from the excited state to the ground
state, what type of energy might we observe being
released?
5. Why are there different colors seen when different
elements move from excited to ground states?