Periodic Table: Classification of Elements

A periodic table is a tabular arrangement of the elements according to their atomic numbers so that elements with similar properties are in the same column. The elements in the periodic table are grouped as metals, nonmetals, and metalloids. Dmitri Mendeleev and Lothar Meyer published the first periodic table in 1869. He showed that when the elements were ordered according to atomic weight, a pattern resulted where similar properties for elements occurred periodically.

Metals are shiny solids with characteristics of high melting points and densities. They have low ionization energy and low electronegativity. Metals makeup more than 75% of the elements in the periodic table.

Metals are characterized by the following physical properties:
1. They have metallic shine or luster.
2. They are usually solids at room temperature.
3. They are malleable. Malleable means that metals can be hammered, pounded, or pressed into different shapes without breaking.
4. They are ductile meaning that they can be drawn into thin sheets or wires without breaking.
5. They are good conductors of heat and electricity.


Nonmetals are elements that have high ionized energies and electronegativity. There are 17 nonmetals in the periodic table.

Nonmetals are characterized by the following properties:
1. They rarely have metallic luster.
2. They are usually gases at room temperature.
3. Nonmetallic solids are neither malleable nor ductile.
4. They are poor conductors of heat and electricity.


Metalloids have ionization energy and electronegativity between those of nonmetals and metals. The six metalloids are B, Si, Ge, As, Sb, and Te. The properties of the metalloids have some same characteristics as the metals and nonmetals.



Elements in the periodic table are arranged in periods (rows) and groups (columns). Each of the seven periods is filled sequentially by atomic number.

Periods
Periods are rows of elements are called periods. The period number of an element signifies the highest energy level for an electron in that element. The number of elements in a period increases as you move down the periodic table because there are more sub levels per level as the energy level of the atom increases.

Groups
Columns of elements are called groups. Groups are elements that have the same outer electron arrangement. The outer electrons are called valence electrons. Because they have the same number of valence electrons, elements in a group share similar chemical properties. The Roman numerals listed above each group are the usual number of valence electrons.


Alkali Metals are found in group 1 of the periodic table. They are highly reactive metals that do not occur freely in nature. These metals have only one electron in their outer shell. Like all metals, the alkali metals are malleable, ductile, and are good conductors of heat and electricity. The alkali metals are softer than most other metals.

Example of an Alkali Metal: Sodium
external image sodium.jpg

Alkaline Earth Metals are the elements in the second column of the periodic table, and they are very similar to the alkali metals.

Example of an Alkaline Earth Metal: Barium
the_element_barium.jpg

Halogens are five non-metallic elements found in group 17 of the periodic table. They are fluorine, chlorine, bromine, and iodine.

Noble Gases are also called rare gas elements, and they all occur in nature as gases. Noble Gases make up the last column in the periodic table. The noble gases fulfill the octet rule by having a full outer level with 8 valence electrons.


Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are semi-conductors. This means that they can carry an electrical charge under special conditions. This property makes metalloids useful in computers and calculators.

Non-Metals are electrically and heat conductive. Non-metals are usually nonreactive. They can be either solid, liquid or gas. Their solid forms are more commonly brittle as a solid and not ductile like metals. They usually have lower densities and melting points than metals .

Example of a Non-Metal: Aluminum
external image Al.jpg
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Other Metals are located in groups 13, 14, and 15. While these elements are ductile and malleable, they are not the same as the transition elements. All of these elements are solid and have a relatively high density .

Transition Metals are the 38 elements in groups 3 through 12 of the periodic table. Like all metals, the transition elements are both ductile and malleable, and conduct electricity and heat. Their valence electrons are present in more than one shell.


Rare Earth Metals are composed of the Lanthanide and Actinide series. One element of the Lanthanide series and most of the elements in the Actinide series are called trans-uranium, which means they are man-made.



Here's how the periodic table looks like:
external image periodic_table.gif


Review Questions:

1. How many Nonmetals are there?
A.15
B. 5
C. 17
D. 10

2. When was the periodic table invented and who invented it?
A. 1925; Albert Einstein and Lothar Meyer
B. 1869; Dmitri Mendeleev and Lothar Meyer
C. 1883; Sigmund Freud and Dmitri Mendeleev
D. 1784; Albert Einstein and Sigmund Freud

3. Compared to metals, nonmetals are:
A. More brittle as a solid.
B. Better electrical conductors.
C
. More ductile as a solid.
D. Better conductors of heat.

4. List at least 3 differences between Metals and Non-Metals.


Here is a FUN crossword puzzle to refresh your memory:
Crossword Puzzle
Click Answers HTML for answers!



Answers to Review Questions:
1-C, 2-B, 3-A, 4- 1. Metals have
a metallic shine or luster and Non-Metals rarely do.
2. Metals are good conductors of heat and electricity and Non-Metals are not.
3. Metals are solid at room temperature and Non-Metals are gases.




http://chemistry.about.com/library/blperiodictable.htm
http://www.facts-about.org.uk/science-periodic-table.htm
http://modelscience.com/PeriodicTable.html