Modern Atomic Theory
Chapter 4.3 Notes

Niels Bohr (1885-1962)
1. Niels Bohr (1885-1962) was a
Danish physicist who worked with
Rutherford.
A. Agreed and worked with
Rutherford’s model of the atom.
B. Bohr’s model of the atom focused on the arrangement of electrons.

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 change.

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 them.

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 energy.
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 an electron moves between energy levels?
• The size of the jump between energy levels.

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 way.

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 orbital

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 orbital.

Energy Levels, Orbital, and Electrons
Energy
Level
1
Multiply by: Number of
Orbitals
X self
Multiply by: Maximum number of
Electrons
X 2
2 X self
3 X self
4 X self
X 2
X 2
X 2

Energy Levels, Orbital, and Electrons
Energy
Level
Multiply by: Number of
Orbitals
Multiply by: Maximum number of
Electrons
1 X self 1 X 2 2
2 X self 4 X 2 8
3 X self 9 X 2 18
4 X self 16 X 2 32

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.