Arrangement of Periodic Table
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Transcript of Arrangement of Periodic Table
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Periods
The elements are arranged on the periodic
table in increasing order of atomic number.
Firsthydrogen- then helium
Below hydrogen is lithium- then to its right
- beryllium, boron, and so forth on across
with increasing atomic number.
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Periods
The elements on the periodic table are arranged so
that their atomic numbers increase in order from
left to right. There is a special name given to the
horizontal rows on the periodic table.First Period - the first row, the one containing
hydrogen and helium
Second Period - the second row
And so on.
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Periods
Why helium, with atomic number 2, is put way
over on the right side instead of next to
hydrogen?
The reason is that the chemical properties of
helium are similar to those of the other elements
in the far right column. They are called the inert
gases because they are all very unreactive gases.
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Rememberthat the periodic table is arranged so
that elements with similar chemical properties are
lined up in vertical columns. It would not be
correct to place the inert gas, He, in the second
column, the one just to the right of H, because
He's properties are not like those of the other
elements in the second column (Be, Mg,etc.)
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Elements in the second column - (Be,
Mg, etc.) - are all reactive metals, notinert gases
In many ways, Hdoes not belong in the
first column either, but it is usually putthere anyway.
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Groups or Families
The vertical columns on the periodic table have specialnames, too.
Remember that all elements in a group or family have
similar chemical properties (except H in some cases).
Each group is represented by a Roman numeral and letter.
They are shown in this periodic table at the top of each
group.
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Groups
Notice that the first group, the one that starts
with H,is represented by Ia and the one right
next to it is represented by IIA.
Then you have to skip all the way across to
boron, B (atomic number 5), to find group IIIA,and then they continue on across--IVA, VA,
VIA, and VIIA.
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The last group, the inert gases, which is shown here as
group 0
, is sometimes represented byVIIIA
and
sometimes byVIII
, sometimes by neither one of those,
and sometimes it has no label at all.
Notice that the groups in the middle part of the table are
represented by Roman numerals followed by the letter
"B" instead of "A." Those groups with the letter "B" are
called thetransition metals
, or transition elements. Thosewith the letter "A" (and 0) are called the
representative
elements
.
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Notice that the transition elements start with group IIIB (not IB),
then IVB, VB, VIB, VIIB. VIIIB is really weird because sometimes it
doesn't have the B and also it represents three vertical columns
rather than just one. Then after VIIIB (or VIII) comes IB and then
IIB and we continue on with IIIA and so forth. That is kind of an
odd way of making these designations, but it is a useful one. Worse
still, there are other ways to number the groups.
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Alternate Groups
This particular arrangement or designation of the group
numbers is used primarily in the United States and mostof the textbooks that have been written in the U.S. over
the past several decades have used this group designation.
I will call it the "Standard American Designation".
Internationally, a different designation is used. That
different designation is often used in commerciallyprepared periodic tables called the "International
Designation."
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Alternate Groups
The international designation puts all of the "A" groups
on the left side of the table and all of the "B" groups onthe right side. The international designation starts out
with Ia then IIA (same as the American) then group
IIIB in the U.S. system is called group IIIA, then IVA,
then VA, then VIA, then VIIA, then VIII. Then we have
IB (which is the same), IIB (the same), then IIIB, IVB,VB, VIB, VIIB and O for the inert gases
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Alternate Groups
If you think about the older short form of the periodic
table being pulled apart to create the long form, those
elements pulled left got the international "A" designation
and those that were pulled right got the international "B"
designation. As for the American approach, those
elements that best matched the family characteristics gotthe "A" designation and those elements that ended up in
the middle of the table got the "B" designation..
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Alternate Groups
Incidentally, there is a movement afoot to come up with still
another way of designating the elements, which I will call the"New Designation." It has some merit because it gets rid of
the A's and B's and group VIII becomes three groups. That
method is to simply number the groups from 1 to 18 all theway across the periodic table. You should also write that on
example 1 so that you will have it for reference. Other
designations have also been proposed and the matter is notyet fully resolved.
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The international designation has the advantage of having
all the "A" groups on the left side of the periodic table
and all the "B" groups on the right side of the periodic
table. The American designation has the advantage of
having all the "A" groups being the representative
elements and all the "B" groups being the transition
elements. I think that has a little bit more validity and so
that's the way we will do it in this course. The newdesignation has the advantage of not having any "A"
groups or "B" groups.
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We use the Standard American Designation. However, you
should realize that the properties of the elements are dependent
on their locationin the periodic table rather than on whatnumbersand lettersare used to designate them. That is really
the important thing. After this lesson, you should be able to
look at where oxygen is on the periodic table and talk about theproperties of oxygen based on that location on the periodic
table. Whether you say it is in group VIA or group VIB or
group 16 really doesn't matter. Except for purposes ofconvenience or identification, you should be able to ignore the
group designations.
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Special Groups
Certain groups on the periodic table are given specific
names with which you need to be familiar. For example,
the elements in the last group (group O) are called the
inert gases. Sometimes they are called the noble gases.
Also, the elements in group VIIA are called the
halogens (F, Cl, Br, I, At). The elements in group IA
(except for hydrogen) are called the alkali metals andthe elements in group IIA are called the alkaline-earth
metals.
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Metals Nonmetals
In addition, there are some other designations on
the periodic table that you need to know. Most of
the elements on the periodic table shown below
are greenin color. Those elements are metals. Theelements that are shown in redare the nonmetals.
The orange (or brown)ones (He, Ne, etc.) are the
inert gases. (They are also nonmetals.)
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Metals Nonmetals
Notice that the dividing line between the metals and
nonmetals starts at aluminum, a metal, and goes
down diagonally to the right. So it is really easy to
figure out where the dividing line is between themetals and the nonmetals. Note that hydrogen is
classified as a nonmetal, even though this periodic
table shows it way over on the left side with the
alkali metals.