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Modern Atomic Theory
Chapter 4.3 Notes
Niels Bohr (1885-1962)
1. Niels Bohr (1885-1962) was a
Danish physicist who worked with
A. Agreed and worked with
Rutherford’s model of the atom.
B. Bohr’s model of the atom
focused on the arrangement of
Niels Bohr (1885-1962)
C. Bohr’s model of the atom
appears to be similar to the solar
system with planets revolving
around the sun.
D. In Bohr’s model electrons
move with constant speed in
fixed orbits around the nucleus.
Energy Levels
2. Energy levels are the possible
energies that electrons in an atom
can have.
A. Each electron in an atom has a
specific amount of energy.
B. If an atom gains or loses energy,
the energy of an electron can
Energy Levels
Ex. 1) Steps
Picture energy levels as steps in a
staircase. As you move up or down the
staircase, you can measure how your
position changes by counting the number of
steps you take. Although you can step up
and down you can not stand between steps.
Electrons follow the same rules. They can
only exist on energy levels, not between
Energy Levels
• The landing at the bottom of the staircase is
like the lowest energy level in an atom.
• Each step up represents a higher energy
level. The distance between two steps
represents the difference in energy between
two energy levels.
• There would need to be a different staircase
for each element because no two elements
have the same set of stairs (energy levels).
Energy Levels
C. An electron in an atom can move
from one energy level to another
when the atom gains or loses
D. Electrons can move up or down
energy levels based on how much
energy is gained or lost.
Energy Levels
E. Scientists can measure the
energy gained when electrons
absorb energy and move to a
higher energy level. They can
measure the energy released
when the electron returns to a
lower energy level.
Energy Levels
Ex. 2) The light emitted from fireworks is
due to the movement of electrons
between energy levels. Heat produced by
the explosion causes some electrons to
move to higher energy levels. When
those electrons move back to lower
energy levels, they emit energy. Some of
that energy is released as visible light.
Different colors of light are produced due
to the fact that no two elements have
the same set of energy levels.
Energy Levels
F. What determines the amount of
energy gained or lost when
electron moves between energy levels?
The size of the jump between energy
Erwin Schrodinger
3. Erwin Schrodinger develops
mathematical equations to
describe the motion of electrons
in atoms. His work leads to the
electron cloud model.
Erwin Schrodinger
A. Bohr was correct in assigning energy
levels to electrons, but he was incorrect
in assuming that electrons moved like
planets in a solar system. We now know
that electrons move in a less predictable
Electron Cloud Model
B. The electron cloud model is a visual
model of the most likely locations for
electrons in an atom.
C. The cloud is denser at those locations
where the probability of finding an
electron is high.
D. Scientists use the electron cloud
model to describe the possible locations
of electrons around the nucleus.
Atomic Orbital
4. An atomic orbital is a region of space
around the nucleus where an electron is
most likely to be found.
A. An electron cloud is a good
approximation of how electrons behave in
their orbital.
B. The level in which an electron has the
least energy, the lowest energy level, has
only one orbital.
C. Higher energy levels have more than one
Atomic Orbital
Ex. 3) Assume you had a map of the school
and you were to put a dot on the map
whenever you visited different areas of
the school for one week. After that week
the areas on the map with the most
amount of dots would be your orbital.
They describe your most likely locations.
The dots on your map are a good model
of how you usually behave in your
Energy Levels, Orbital, and Electrons
Multiply by: Number of
Multiply by: Maximum
number of
X self
X self
X self
X self
Energy Levels, Orbital, and Electrons
Multiply by: Number of
Multiply by: Maximum
number of
X self
X self
X self
X self
Review Question
D. How many electrons can
be in each orbital?
• 2
Electron Configuration
5. An electron configuration is the
arrangement of electrons in the orbital of
an atom.
A. The most stable electron configurations is
one in which the electrons are in orbitals
with the lowest possible energies.
B. When all of the electrons in an atom have
the lowest possible energies, the atom is
said to be in its ground state.
Electron Configuration
C. When an atom absorbs
enough energy its electrons may
move to an orbital with a higher
energy level.
D. When this happens the atom
is said to be in an excited state.
Electron Configuration
E. An excited state is less stable
than the ground state.
F. Eventually, the electron that
moved to a higher energy level
loses energy, and the atom
returns to the ground state.