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NOVA scienceNOW: Island of Stability
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Viewing Ideas
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Before Watching
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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.
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Discuss the Periodic Table of the Elements. Have students
refer to a copy of the periodic table and answer the following
questions:
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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.
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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.
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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
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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.
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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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