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NOVA scienceNOW: Island of Stability
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Viewing Ideas
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Before Watching
Use a concept map to review atom-related terms. Concept maps are a way
to visually show how the parts of a system relate to one another. In a concept
map, nouns are used to describe the components of the system (i.e., the
vocabulary term). The relationship between the different components is shown by
arrows, which connect the parts. Each noun is put in a box, and the arrows are
labeled with a verb describing the relationship between components. Have
student pairs find the definitions for the following terms in their textbook
(or other resource). As a class, discuss each term. Then, have students create
a concept map that shows the relationships among the terms.
atom: The smallest unit of an element that retains the chemical
properties of that element.
electrons: Negatively charged particles that orbit the nucleus of an
atom.
element: A substance that cannot be broken down into smaller components
by chemical reactions. There are 92 naturally occurring elements.
isotope: An atom that has the same atomic number as another atom but
that has a different atomic mass.
nuclear forces: The binding forces in the nucleus of atoms that act over
short distances and help overcome the protons' repelling forces.
nucleons: Particles that make up the nucleus of an atom. Protons and
neutrons are nucleons.
nucleus: The positively charged core of an atom that contains most of
the atom's mass and all of its protons and neutrons.
neutrons: Particles in the atomic nucleus without an electrical charge.
Protons and neutrons have nearly identical masses.
protons: Particles in the atomic nucleus with a positive charge. The
number of protons determines the identity of the element. Discuss the Periodic Table of the Elements. Have students refer to a
copy of the periodic table and answer the following questions:
How are the elements' atomic numbers used to arrange them on the
periodic table? Elements are arranged by a successive increase in atomic
number (i.e., the number of protons in the nucleus) as one moves across each
row from left to right. This number uniquely identifies each element. What is the general relationship between the atomic number and the
atomic mass weight? For most elements, the atomic mass is double the atomic
number. For elements such as tin, the atomic mass is slightly more than double
the atomic number. This is because atomic weight is an average weight of all
the isotopes of an element, and an element's isotopes have different numbers of
neutrons. How might isotopes of an element differ from each other? An
element's isotopes have different numbers of neutrons. In addition, some
isotopes are more stable than others.
After Watching
Model the size of an atom. Divide the class into pairs or
teams, and provide each one with a coin—a penny, dime, nickel, or
quarter. Different teams can have different coins. Tell students that the
diameter of the nucleus is about 1/10,000 the diameter of an atom. (Most atoms
range in diameter from 1 x 10-10 to 5 x 10-10 meters.)
The diameter of an average nucleus is 1 x 10-14 meters, 10,000 times
smaller than the diameter of an atom.) Have teams measure the diameter of their
coin and calculate the diameter of an atom having a nucleus that size. Give
them maps, and have them identify the location of a place this same distance
away from school.
Establish that atoms are primarily empty space. Although an atomic
nucleus is tiny relative to the size of an atom, it contains almost all the
atom's mass—an atom is primarily empty space. To make this point, have
students calculate how much a familiar object would weigh if it had no empty
space and were made entirely of atomic nuclei. Begin by having students select
a common object (e.g., a book, piece of chalk, ball) and calculate its volume
in cubic centimeters. (You may have to review how to calculate the volume of
basic three-dimensional shapes, such as a cube, sphere, or cylinder.)
Have students estimate the object's mass. Remind them that even solid objects
are mostly empty space. Then, calculate how much the object would weigh if it
were made entirely of hydrogen nuclei (i.e., no empty space). Multiply the
volume by 1 x 1015 grams/centimeter3, the density of an
average hydrogen nucleus. How much would the object weigh if it were as dense
as a hydrogen nucleus? (An object with the volume of a penny would weigh
more than 30 million tons. This is about a quadrillion times denser than an
object with such volume would normally be.) Students should realize that,
for atoms to weigh as little as they do, they must not be consistently dense
and must instead be mostly empty space.
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Demonstrate that a concentrated mass can occupy a small space. Give
students a ball of clay one to two inches in diameter and a small box, such as
a shoebox. Have them calculate the density of the empty box, the density of the
clay ball, and the density of the box with the ball of clay in it. (Density
equals mass divided by volume.) Students will see that the mass of the box
and clay is nearly identical to the mass of the clay alone, drawing a strong
parallel to the relationship between an atom and its nucleus. Tell students
that prior to 1911, scientists believed that the mass of an atom was evenly
distributed rather than concentrated at the center. Physicist Ernst Rutherford
(1871-1937) passed a beam of radioactive alpha particles (which are extremely
tiny atomic particles) through thin gold foil and studied how the foil
scattered the particles. He observed that some ricocheted off at an angle and
some bounced straight back, like balls hitting a wall. But most passed straight
through with little or no deflection. The pattern of the scattered particles
suggested that each atom making up the gold foil (and matter in general) is
largely empty space with a relatively massive nucleus at its center. Relate the
box-clay model to the structure of an atom. (Protons and neutrons make up
more than 99% of the mass of an atom. Protons and neutrons are found in the
nucleus; electrons, which are considerably smaller and less massive than
protons and neutrons, are found far outside the nucleus. So, just like
the box, atoms contain large regions of empty space and have their
mass—like the clay—concentrated in one place.)
Links
Karl Iagnemma: On the Nature of Human Romantic Interaction
www.karliagnemma.com
On Karl Iagnemma's personal Web site, find information on his newest book of short stories, read reviews of his writing, and more.
Field and Space Robotics Laboratory
robots.mit.edu
On this Web site, learn about Iagnemma and his colleagues at MIT, view summaries of their latest robotics projects, and see photographs from MIT robotics labs.
The Robotics Alliance Project
robotics.nasa.gov
NASA's Robotics Alliance Project Web site provides a hub for robotics education and career resources. Find information on building your own robot, join robotics competitions, and more.
Robotics: Sensing, Thinking, Acting
www.thetech.org/exhibits/online/robotics
This online exhibit, developed by the Carnegie Science Center in Pittsburgh, PA, focuses on the world of intelligent machines. Control your own remotely operated vehicle, see robot art, and hear how scientists, artists, and others view the role of robots in our lives.
Kiss Institute for Practical Robotics
www.kipr.org
KIPR seeks to improve learning skills through robotics. On its Web site, learn about institute classes in robotics for any age; participate in Botball, a game that gives students hands-on experience in designing, building, and programming robots; and more.
Books
On the Nature of Human Romantic Interaction
by
Karl Iagnemma. Dial Press Trade Paperback, 2004.
123 Robotics Experiments for the Evil Genius
by
Myke Predko. McGraw-Hill/TAB Electronics, 2004.
The Robot Builder's Bonanza: 99 Inexpensive Robotics Projects
by Gordon McComb. McGraw-Hill/TAB Electronics, 2000.
Articles
"Visual Wheel Sinkage Measurement for Mobile Robot Mobility Characterization,"
by C. Brooks, K. Iagnemma, and S. Dubowsky. Autonomous Robots Volume
21, Number 1, pp. 55-64, August, 2006.
"Hollywood Calls"
by Liz Karagianis. Spectrum, Spring 2005, Volume XVII, Number 2.
web.mit.edu/giving/spectrum/spring05/hollywood_calls.html
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