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Unit 5
The Periodic Table
As our picture of the atom becomes more
detailed, we find ourselves in a dilemma.
当我们对原子了解的越来越详细时，我们
发现我们其中处在两难之中己。
With more than 100 elements to deal with, how can we keep all this information straight?
由于
超过
100
种元素
要处理，
我们怎样能理顺所有的信息？
One way is
by using the periodic table of the elements.
一个方法是使
用元素周期表。
The
periodic
table
neatly
tabulates
information
about
atoms.
周期表整齐地列出了原子信息的表格。
It
records how many protons and electrons
the atoms of a particular element contain.
它记录了一个具体的元素的原子包含多
少质子和电子。
It permits us to calculate the number of neutrons
in the most common isotope for most elements.
它允许我们
为大多数元素计算最常见的同位素中的中子的数量。
It
even
stores
information
about
how
electrons
are
arranged
in
the
atoms
of
each
element.
它甚至储存了每个元素的原子周围是如何安排电子的信息。
The
most
extraordinary
thing
about
the periodic table is
that it was largely developed before anyone knew
there were protons or neutrons or electrons in
atoms.
关
于周期表的最杰出
的事情是在任何人知道在原子周围有质子、中子或者电子之前被提出来。
Not
long
after
Dalton
presented
his
model
for
the
atom
(an
indivisible
particle
whose
mass
determined
its
identity ),chemists began preparing
listings of elements arranged according to their
atomic weights .
不久之后道尔顿提出他的
原
子模型
（一个不可分割的粒子的质量决定其特性）
科学家开始准
备按他们的原子的重量安排元素表。
While working out
such tables of elements ,these
scientists observed patterns among the elements .<
/p>
当规划出这些元素的表，这些科学家观察这
些元素的模型。
For
example
,it
became
clear
that
elements
that
occurred
at
specific
intervals
shared
a
similarity
in
certain
properties
.
例如，越来越清晰的表明某些特定间隔的元素共享某些相似的性质。
Among
the
approximately
60
elements
known
at that time ,the fourth and eleventh ,the fifth
and twelfth ,and so on .
在那个时候大约
< br>60
个已知元素中
,
第四和第十
一
,
第五和第十二（拥有相似性质）
,
等等。
In 1869,
Dmitri Ivanovich Mendeleev, a Russian chemist,
published his periodic table of the elements.
在
1869
年，德米
特里·
伊万诺维奇·
门捷列夫
，
一位俄罗斯化学家，
出版了他的元素周期表。
Mendeleev prepared his table by
taking into
account both the atomic
weights and the periodicity of certain properties
of the elements.
门捷列夫综合考虑元素
的原子量
和性质的相似性制成了他的元素周期表。
The elements were arranged primarily in
order of increasing atomic weight.
元素
主要按照原子量增加的顺序排列。
In
a
few
cases,
Mendeleev
placed
a
slightly
heavier
element
with
similar
chemical
properties in the
same row.
在一些情况里，门捷列夫把稍微重一点
且性质相似的（元素）放在一列中。
For
example, he
placed tellurium (atomic
weight = 128) ahead of iodine (atomic weight =
127) because tellurium resembled sulfur and
selenium
in its properties, whereas
iodine was similar to chlorine and bromine.
例如，他把碲
(
原子量
= 128)
排在碘
(
原子量
= 127)
前
面，因为碲在它的特性方面类似硫和硒，而碘类似于氯和溴。
Mendeleev left a number of gaps in his
table.
门捷列夫在他的元素周期表中留下了许多空格。
Instead of looking upon
those blank spaces as defects, he
boldly predicted the existence of elements as yet
undiscovered.
他没有认为这些空格的出
现是周期表的缺陷，而是大胆的预言还有未被发现的元素的存在。
Furthermore, he even predicted the
properties of some
of these missing
elements.
而且，他甚至预言一些这些未发现的元素的特性。
In succeeding years, many of the gaps
were
filled in by the discovery of new
elements.
在以后的许多年中，
< br>许多空格被发现的新元素填入。
The
properties were often
quite close to
those Mendeleev had predicted.
性质经常十分接近于门捷列夫已经预言的那些性质。
The predictive value
of this
great innovation led to the wide acceptance of
Mendeleev's table.
这个伟大革新的预
言价值是门捷列夫的元素周期
表被广泛接受。
It is now known that
properties of an element depend mainly on the
number of electrons in the outermost energy level
of
the
atoms
of
the
element.
现在知道一种元素的性质主要取决于元素原子最外层能级的电子数目。
Sodium
atoms
have
one electron in their outermost energy
level (the third).
钠原子在它们的最
外层能级
(
第
3
层
)
里有一个电子。
Lithium atoms
have
a
single
electron
in
their
outermost
level
(the
second).
锂原子在他们的最外层能级
(
第
2)
里有一个单电子。
The
chemical properties of sodium and
lithium are similar.
钠和锂的化学性质是相似的。
The
atoms of helium and neon have
filled
outer electron energy levels, and both elements
are inert.
氦和氖的原子充满电子能级，
并且两种元素都是不活泼的。
That
is, they do not undergo chemical reactions
readily.
也就是说，他们不容易发生化学反应。
Apparently, not only are
similar
chemical
properties
shared
by
elements
whose
atoms
have
similar
electron
configurations
(arrangements)
but
also
certain configurations
appear to be more stable (less reactive) than
others.
显然，不仅是具有相似的电子构造
(
安排
)
的原子
的元素具有相似的化学性质，而且某些构造看起来比其它（构造）是更稳定
(
更少活性
)
的。
In Mendeleev's table, the elements were
arranged by atomic weights for the most part, and
this arrangement revealed the
periodicity of chemical properties.
在门捷列夫的周期表中，
大部分元素
按照原子量安排，
而且这种安排显示了化学性质
的周期性。
Because the number of
electrons determines the element's chemical
properties, that number should (and now does)
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