- University of Virginia
- Physics Department
A Physical Science Activity
2003 Virginia SOLs
- define "quantum";
- describe atomic structure as quantized.
Discrepant Event: Light Emission
- Use a lightbulb, flashlight, or match to demonstrate the emission of light.
Light the source of your choice, and ask students why the source is emitting
light. If they respond, "Because it is burning," ask them what they
think happens at the atomic level when something burns. Explain to them that
when you "light" the source, you are adding an amount of energy
to it. For an example, consider a neon bulb. When voltage is applied across
the bulb, current flows through the gas within it. This flow of electrons
impacts the electrons of the neon atoms within the bulb. In these collisions,
kinetic energy is given to electrons with the atom, and they move to a higher
energy level or "quantum" state. They may only remain there for
an instant. Then they are pulled back down to their original quantum state.
Since their energy must be conserved, they emit energy in the form of light
energy. It is this light energy that we see when a light bulb, match, or flashlight
To aid in this difficult concept, follow the link to http://www.colorado.edu/physics/2000/quantumzone/bohr2.html.
The applet halfway down the page allows teachers and students to interact
with an atomic model. Explain to students that each dotted circle surrounding
the nucleus represents a different energy or quantum level. The farther away
from the nucleus, the higher the quantum state. By clicking on a higher energy
level, a photon of light energy is shot into the orbiting electron. The electron
then has gained enough energy to attain orbit at a higher quantum level. Eventually,
the electron will emit a photon of light energy and drop to a lower quantum
energy level, where it is more stable.
Students often find the idea that electrons in atoms exist in quantized energy
levels very difficult to grasp since most of our everyday experiences are with
phenomena that are continuous. However, once students are introduced to a macroscopic
example of quantization, they will become more comfortable with the idea. The
activity described is one that a teacher could integrate into a class discussion
of the quantum model of the atom.
- Stairs, chorus risers, or bleachers and/or
- Bookshelf and/or
- Introduce the definition of quantum to students. Many may have heard
the term "quantum leap" or may have seen the old television show by that title.
In this context, quantum is referring to a very sudden, discrete change or
leap. This is very much how electrons behave within an atom when they absorb
or emit energy. Electrons cannot be halfway between two energy levels.
- Since we do not usually think of nature in a quantum sense, students will
benefit from some common, quantized examples. One example is a staircase.
When we ascend stairs, we can only be on a step-we cannot rest in between
steps. (Students may argue that they can be "between" steps by having their
feet on different steps, but still they are not truly between steps.
Before introducing this example, explain to the students that this example
is only a model of the idea. Also, establish a definition for what "being
on a step" means.) Once the students accept the model, the arrangement of
electrons within an atom can be accomplished by lining two students on one
stair then several on a second stair (up to eight) and so on. Additionally,
the students will readily see that in order to move from their assigned quantum
state (stair) to a higher one, energy must be put into the system; that is,
they must climb to the next available step.
- Another example of quantization is a bookshelf where books can only exist
on one shelf at a time and never in between.
- Chairs can also be used to demonstrate the concept. Line up several chairs
or desks (perhaps in groups of two, eight, and eighteen to replicate the electron
arrangement for the first three energy levels of an atom). Place students
in the chairs playing the role of electrons. Emphasize the impossibility of
sitting between chairs to parallel the idea that electrons will not exist
between energy levels.
- An important short-fall in this demonstration is that within an atom, the
energy levels are not evenly spaced as in the examples cited. The bookshelf
example could include a bookshelf with moveable shelves that could be variably
- What are the 3 main particles that make up atoms?
- Can these particles be broken down into smaller particles?
- Do we ever know exactly where an electron is as it orbits a nucleus?
- What experiment did Ernest Rutherford perform and what did it tell us about
the nature of atoms?
- Can a chemical change alter the identity of an atom (change its atomic number)?
- Can electrons exist between quantized energy levels?
- How many electrons can each of the first 3 energy levels hold?
- Students conduct historical research on the development of the
quantum model of the atom.
- Students construct a time-line of the major developments of
the atomic theory from ancient to modern times.
Students with Special Needs
Some students may not be able to participate in the stairs portion of the activity.
Click here for further
information on laboratories with students with special needs.
Have students answer questions by conducting internet or library research.
The included "additional background information" link is very helpful.
Answers to questions
- proton, neutron, electron
- the proton and neutron can be broken down into smaller particles. So far,
the electron has not been shown to be made up of smaller particles.
- no, but we can predict an electron's position using probability functions
first developed by Erwin Schrodinger.
- Rutherford performed the 'Gold Foil Experiment' and found that small charged
atomic particles called alpha particles could be scattered by shooting them
through thin gold foil. This showed that there were dense nuclei within atoms
with a charge. This charge allowed the alphas and nuclei to interact by the
Coulomb force, and alphas were scattered from their original paths.
- no, a chemical reaction can only affect the number of electrons within atoms
and how they are bonded.
- no, electrons can only exist in quantized energy levels.
- 2,8,18 respectively