s8pe-20704-ca
12/19/05
4:45 PM
MAZER
Page 228
Exceptions
We’ve seen a few trends in the physical properties of the elements in the
periodic table. Knowing these trends makes the periodic table a valuable
tool. If two elements are close together in the periodic table, you can
feel fairly certain you can identify some relationship between them.
Carbon in the form of
diamond has one of the
highest melting points of
any element. It is also one
of the hardest substances
on Earth.
Or can you? For example, carbon, which has the atomic number 6,
and nitrogen, which has the atomic number 7, could not be more
different. Carbon is a solid up to about 3,700°C. Nitrogen, however, is
a gas to –196°C. Obviously, the difference of a proton in the atom’s
nucleus makes a huge difference in the properties of the two elements.
This goes to show that atomic structure is very complex. We can only
present a simplified picture of it here. Not even the most knowledgeable
scientists, however, know exactly why some atoms behave the way they
do. With each question answered, it seems another question arises.
Remember, scientists realized that certain elements had related
properties before they knew about atomic structure. The two ideas were
separate. They were only later linked. There were many false starts. But
each false start brought scientists closer to what they know today.
So, when you look at the periodic table, don’t think of it as just a
collection of symbols. Think of it as a reflection of the relationships
among the elements. Think of it as a map of the elements. Think of it
as a reflection of atomic structure.
check your reading
Which element has one more proton than carbon?
With only an additional
proton in its nucleus,
nitrogen is very different
from carbon. It is a gas
down to –196°C.
KEY CONCEPTS
CRITICAL THINKING
1. How have scientists used the
periodic table in making new
discoveries? (8.7.c)
4. Predict Barium (Ba) is in Group
2. Recall that atoms in Group 1
lose one electron to form ions
with a 1+ charge. What type of
ion does barium probably form?
2. Why don’t atoms simply get
larger as you read across the
periodic table? (8.7.c)
3. Which elements in the periodic
table are better conductors
of heat? (8.7.c)
228 Unit:2 The Structure of Matter
5. Interpret Name two elements
that are side by side on the
periodic table that do not
reflect the general trend in
melting points for the periods.
CHALLENGE
6. Infer Long ago, chemists
hoped to find a way of turning
any element into gold. Do you
think this is possible today?
Why or why not?
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