Prescriptive Activities: Electrons: PF#40
Student Page
Materials:
 Student handout
Directions: Read and complete the activities/questions below
The model of the atom has changed over time as more experiments have been performed
and more evidence has been collected. Consider the pictures below that show how the
model has changed over time. The models have changed as we have gotten more
information about the nature of the atom.
An early model of the atom was the indivisible ball “atoms” as known by the Ancient Greek
philosopher Democritus. The belief was that there was some small particle that could not
be divided up any more. Later came the plum pudding model that was designed by
Thomson. Is this model the negative charge of the electrons and the positive charge of the
nucleus were spread out in the atoms. The Rutherford model of the atom designed after
the gold foil experiment came next. In this model, there is a nucleus with a positive charge
and a large area outside of the nucleus that made up the rest of the atom and the electrons
could be found in the large area. The Bohr model of the atom followed. In the Bohr model,
nucleus was the center but now the electrons “lived” in energy levels. We knew this
because whenever the electrons changed levels light of a particular color was gained or
released. Many people started believing that the electrons were like planets with the sun.
This is not true, because we know now the electrons do not go around the nucleus like
planets. We have an idea about where the electrons can be found in the space around the
nucleus and we can say that we are most likely to find then one place and not another, but
we cannot know for sure where the electron is. This is called the cloud model of the
electron or the quantum model. The cloud shows where you are likely to find the electron.
The darker the cloud, the more likely you are to find the electron there. If the cloud is
lighter, then you are less likely to find the electron there. A wrong idea is to think that the
electrons are like rain in the clouds in the sky. This is wrong because the electron clouds
do not exist, it is just a model showing you where you MIGHT find the electrons. This is
where we are now in our model.
1
Prescriptive Activities: Electrons: PF#40
Student Page
Discussion Questions:
1. Create a cloud showing the chances of finding an electron (a.k.a likelihood
distribution cloud): You are going to make a model of the electron cloud. The
electron cloud does not exist, it is a model or picture of where you are likely to find
the electron. Some places in the cloud, you are more likely to find the electron and
other places your are less likely to find it. We know that we cannot know for sure
where the electron is, only where it has been and where it might go next. Weird,
but true.
2. Make a likelihood distribution cloud. Take a large sheet of newspaper or similar
paper. Place the paper on the floor and stand above the paper with small ( ½ cm)
yarn pompom1 and 100 paper dots. A paper dot is what is left over after using a
hole punch.
3. From 2 meters above the paper, drop the pompom on the paper. Glue a paper dot
where the pompom hits the paper. Repeat 100 times. You might need a friend.
4. Interpret: Make a circle around all the dots. This is the electron cloud. Circle an area
where there seems to be more dots than another area (denser more dots). The
places where there are a lot of dots means that there would be a great chance that
the electrons would be there: More dots more likely.
5. Answer these questions:
a. What does the area where there are few dots mean in terms of electrons?
b. If you were to drop the ball one more time (101st). Where would you predict
it would most likely fall? Why would it be most likely to fall there?
c. Where would you predict it would not fall? Why would it be less likely to fall
there?
d. How is the paper model similar to an electron cloud model?
6. Consider the model of the atom at the link below. The electrons are in constant
motion around the nucleus.
http://www.regentsprep.org/Regents/physics/phys05/catomodel/cloud.htm
Make a chart comparing how your model and the cloud model are different.
Resources
1Make
a pompom. Look up making a yarn pompom on the web. There are many sites that
have instructions. http://www.make-and-build-dog-stuff.com/homemade-pom-poms.html
http://education.jlab.org/qa/atom_model.html This site asks students to build a nucleus
then goes on to explain the planetary model and why it is incorrect. It also introduces the
BOHR model and electron configuration for teachers who want it. The picture of the
nucleus is very good and could be used for FC 2 atoms as well.
2