Download Electron Distribution Using Peas

Electron Distribution Using Peas
Name:
Introduction:
Could you determine the exact position and momentum of a baseball as it soared through
the air? Of course, you could—by taking a timed series of snapshots of the baseball as it
moved. Why then can’t scientists follow a similar procedure to determine the position
and momentum of an electron?
You can see a moving baseball or its image because of the light bouncing off the
baseball. The effect of light on either the position or the momentum of the baseball is
negligible. By contrast, an electron has such an extremely small mass that light disturbs
it in an unpredictable way. How then can the position and momentum of an electron be
determined?
Knowledge of the behavior of electrons in the atom comes from theoretical work done in
the 1920s by Heisenberg and Schrodinger. Heisenberg postulated that it was impossible
to determine exactly both the position and momentum of an electron at the same instant.
Heisenberg deduced that the more precisely you know the position of an electron, the less
certain you are about its momentum, and vice versa. Because its exact position and
momentum can never be established at any given time, the exact path of an electron
around the nucleus cannot be determined. Instead the quantum-mechanical model of the
atom gives the probabilities of finding an electron in a particular region around the
nucleus.
In this investigation, you will model the probable locations of electrons around
the nucleus of an atom. You will use peas to represent electrons to help you visualize
regions of high and low electron density.
Materials:
Metric ruler, ring stand, dried peas, beaker (150 mL), sheet of butcher paper, marker,
scissors, piece of filter paper, compass (or string tied to your pencil).
Procedure:
1. Fold the filter paper in half and then fold it again into quarters. Using the ruler,
measure up 1.5 cm from the closed point of the paper and make a mark. Make a
small hole in the bottom of the folded filter paper by cutting at the 1.5-cm mark with
the scissors. Insert the cut filter paper into the ring stand to create a funnel with the
small hole at the bottom.
2. Use the compass (or a string) to draw a circle with a radius of 3 cm in the center of a
large sheet of butcher paper. Then draw four more concentric circles 3 cm apart,
around the first circle. Number the rings 1-5, starting from the center.
3. Mark the center of the innermost circle with a large dot; this will represent the
nucleus of your atom. Hold the ring 8 inches about the hole so that the hole in your
filter paper is directly over the dot.
4. Measure out _______mL of dried peas and put them in your 150-mL beaker. Pinch
closed the hole at the base of the filter paper and add the dried peas, or “electrons,” to
the filter. Let go of the filter, allowing the peas to fall through the small hole onto the
target beneath the ring stand. If the peas jam up in the filter, push them gently to keep
them moving.
5. Count the number of peas in each ring around the nucleus, as well as any that fall
outside the rings. Record the data in the table, beginning with the innermost ring
number 1.
6. Gather up the peas and place them in the garbage. Make sure you clean your area up
well; if your area is messy, you will lose points! Return all equipment to the supply
area. Wash your hands.
Data Table:
Ring
Distance from Nucleus
Number of Peas in Ring
Attach a graph of class data to this sheet. After you have completed the graph, answer
the following questions and turn in one set of data, post-lab questions, and a graph per
pair. Make sure both names are on it!
Post-Lab Questions:
1. Judging from your graph, in which region would you be most likely to find electrons?
In which region would you be least likely to find electrons?
2. Were you able to determine the exact path by which each pea (electron) arrived at its
position on the target? How does this finding relate to the quantum theory?