Lesson 6: Arrangement of the Periodic Table

In this section we will discuss some of the basic terminology related to the arrangement of elements on the periodic table. You should get your periodic table from example 1 in your workbook and use it to take notes from this and the other pages in this section.

Periodic Table

Take a look at example 1 in your workbook now. It contains more information than the one shown above on the screen. In most periodic tables at least two numbers are shown in the box for each element, as shown to the right. There will be the atomic number and also the atomic weight. In this periodic table the atomic number is shown in the upper left-hand corner and the atomic weight is shown below the symbol for the element.

atomic number

8
	O
	16.00

atomic symbol

atomic weight

Periods | Groups | Alternate Groups | Special Groups | Metals & Nonmetals

Periods

Notice how the elements are arranged on the periodic table in increasing order of atomic number. There is, first of all, hydrogen--then to its right is helium. Below hydrogen is lithium--then to its right is beryllium, boron, and so forth on across with increasing atomic number.

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. They are called periods. The first row, the one containing hydrogen and helium, is called the first period. The second row is called the second period. And so on.

You may wonder 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. Remember that 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 aren't anything like those of the other elements in the second column (Be, Mg, etc.) They are all reactive metals, not inert gases. In many ways, H does not belong in the first column either, but it is usually put there anyway for reasons that we will get into later.

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Groups

The vertical columns on the periodic table have special names, too. They are called groups or families. 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.

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.

Periodic Table with Groups and Periods

Groups

IIA

IIIB

IVB

VIB

VIIB

VIIIB

IIB

IIIA

IVA

VIA

VIIA

0 (VIIIA)

P
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r
i
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s

The last group, the inert gases, which is shown here as group 0, is sometimes represented by VIIIA and sometimes by VIII, 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 the transition metals, or transition elements. Those with the letter "A" (and 0) are called the representative elements.

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 most of 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 commercially prepared periodic tables and you should become familiar with it.. I will call it the "International Designation." The international designation puts all of the "A" groups on the left side of the table and all of the "B" groups on the right side. I want you to write in the international group numbers above the American group numbers on the periodic table in example 1 so that you will have them for reference. 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. 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 got the "A" designation and those elements that ended up in the middle of the table got the "B" designation.

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 the way 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 not yet fully resolved.

Periodic Table with Various Group Designations

New

International

IIA

IIIA

IVA

VIA

VIIA

VIIIA

IIB

IIIB

IVB

VIB

VIIB

VIIIB

Std. Am.

IIA

IIIB

IVB

VIB

VIIB

VIIIB

IIB

IIIA

IVA

VIA

VIIA

0 (VIIIA)

P
e
r
i
o
d
s

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 new designation has the advantage of not having any "A" groups or "B" groups. We will use the Standard American Designation. However, you should realize that the properties of the elements are dependent on their location in the periodic table rather than on what numbers and letters are 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 the properties 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 of convenience 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 and the elements in group IIA are called the alkaline-earth metals.

Special Groups on the Periodic Table

^ alkaline earth metals

halogens^

^ alkali metals

inert gases ^

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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 green in color. Those elements are metals. The elements that are shown in red are the nonmetals. The orange (or brown) ones (He, Ne, etc.) are the inert gases. (They are also 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 the metals 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.

Periodic Table Showing Metals, Nonmetals and Inert Gases

Let me make a few comments about the periodic table shown in example 1 in your workbook. It is the standard periodic table for this course. It has the symbol, the atomic number (in the upper left) and the atomic weight (below the symbol) for each element. In this course, you can expect to have a periodic table like this available to you anytime you take a test, a quiz, do your homework, or whatever. It is a source of atomic numbers, symbols, and atomic weights. Notice that it does not have the names on it. You need to be familiar with the relationship between names and symbols, which is why you had to memorize the names and symbols of the more common elements earlier in the course. This is the periodic table that you will become very familiar with as the course proceeds.

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CH 104: INTRODUCTORY CHEMISTRY

CH 104: INTRODUCTORY CHEMISTRY

Lesson 6: Arrangement of the Periodic Table

Periods

Groups

Alternate Groups

Special Groups

Metals & Nonmetals