arrangement of periodic table

8/10/2019 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.

arrangement of periodic table

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