s8pe-20704-ca
12/19/05
4:44 PM
MAZER
Page 224
KEY CONCEPT
Patterns exist among
the elements.
CALIFORNIA
BEFORE, you learned
NOW, you will learn
Content Standard
• The periodic table organizes
elements according to their
properties
• Elements are classified as metals,
nonmentals, and metalloids
• How the periodic table can be
used to make predictions
• How atomic structure relates to
physical properties of elements
• How the periodic table shows
patterns among properties of
elements
8.7.c Students know substances can be classified
by their properties,
including their melting
temperature, density,
hardness, and thermal
and electrical conductivity.
EXPLORE Trends in the Periodic Table (8.7.c)
VOCABULARY
thermal
conductivity p.227
electrical
conductivity p.227
Are there relationships among
the elements?
1
Find the four elements listed at right on the
periodic table.
2
Arrange them according to their positions in the
periodic table.
WHAT DO YOU THINK?
• How are the elements located in relation to one
another?
• Can you make a generalization about the
densities of elements in a group?
The periodic table is expanding.
CALIFORNIA
Focus
Physicist Ernest Lawrence
constructed the first
cyclotron in January, 1931
in Berkeley, California.
It measured only about
11 cm (4.5 inches).
Today’s cyclotrons can be
as much as 18 m (709
inches or 60 ft) in diameter. Particles may travel 45
km (28 mi) before they
strike a nucleus.
Before 1940, no one had found an element whose atoms had more
than 92 protons in its nucleus. That year at the University of California,
Berkely, scientists Edwin McMillan and Philip Abelson thought they
might be able to make one. They used a device called a cyclotron. The
cyclotron can hurl protons and neutrons towards the nuclei of other
atoms. If some of these particles stick to a nucleus, there is a chance a
different element can form. McMillan and Abelson used the cyclotron
to assemble an element with 93 protons in its nucleus. They decided to
call the element neptunium. The next year, Berkeley scientist Glenn
Seaborg assembled an element with 94 protons in its nucleus, plutonium.
224 Unit:2 The Structure of Matter
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