The Periodic Table of elements is a listing of known elements organized by their atomic number. The Periodic Table was changed over time and the order has changed to have their atomic numbers in order but also by listing them by their properties.
Each row is a period of elements in which chemical properties repeat. Periods tells us many things such as electronegativity and ionization energy and much more. Electronegativity increases as you move left to right from a period. Atomic radius decreases as you move left to right in a period. Ionization energy increases as you move left to right. Elements that are in the same period have the same number electron shells Atomic number also increases as you move left to right in a period in the periodic table.
Trends in electronegativity
The columns are groups or families. The elements in each group have similar properties because they have the same amount of valance electrons in the outer orbital giving each of the elements their unique properties. Dimitri Mendeleev was the first to organize the periodic table.
Table of Elements
| 2 |
| 10 |
| 18 |
| 36 |
| 54 |
| 86 |
| 118 |
|* Lanthanides|| 57
| 71 |
|** Actinides|| 89
| 103 |
In 1869 Russian chemist Dimitri Mendeleev arranged chemical elements by atomic mass. He predicted the discovery of other elements and left space open in his periodic table for them.  Mendeleyev is regarded as the primary discoverer of the periodic table. However, in 1868 (a full year before Mendeleyev), a German chemist named Lothar Meyer designed a table of elements which resembles the present periodic table. Unfortunately he did not publish this work until after the appearance of Mendeleev's first paper on the subject in 1869.
Categories of Elements
Metals, Nonmetals, and Semimetals
Most of the periodic table is composed of metals that are on the bottom left corner of the periodic table and the top right part of the periodic table is the nonmetals and the semimetals are on the middle of the them. semimetals hve properties of metals and some properties of nonmetals, thats the reason why the semimetals are in the midle. Metals Common characteristics: Metallic luster, Generally solids at room temperature, Malleable, Ductile, Conduct heat and electricity, Combine with other metals to form alloys, Form positive ions. Nonmetals Common characteristics: Rarely have metallic luster (shine), usually gases at room temperature, Neither malleable or ductile, Poor conductors of heat and electricity, ussually are as molecules, they Combine with other nonmetals to form covalent bonds, normally form negative ions. Semimetals (Metalloids) are a class of 8 elements that have properties of both metals and nonmetals. Common characteristics are: look metallic but are brittle, neither good conductors or insulators. 
Major categories of Elements
Important Groups/Families of Elements
Groups are the columns of the periodic table. Elements in the same group have similar chemical properties and the same number of valence electrons. The periodic table of elements has diffent groups that have a special name like the Alkali metals (group 1), Alkaline Earth metals (group 2), the Transition metals (all the elements from group 3 to group 12), Halogens (group 17 Known as 7a),and The Noble Gases (group 18 known as 8a).
Properties of the Elements
In the periodic table there are special elements like the elements with the atomic number of 84 and up that are unstable and so they are radio active and can become a different element and release harmful particles like alpha and beta particles and gamma rays that are even more harmful. No element higher than 92 occur naturally, these elements are produced artificially in nuclear reactions. Another type of elements is the elements in group 18 or 8a that are the noble gases that don't bond to other elements and have the electron configuration that all elements are required to have. The alkali metals all react violently in water.
The atomic radius increases as you move down and left.
The ionic radius increases as you move down and left. Cation are smaller and anions are larger.
Metallic Character/Metal Reactivity
Metallic character/Metal Reactivity increase as you move down and left.
1st Ionization Energy
1st ionization energy increases as you move up and right.
Electronegativity increases as you move up and right.
Nonmetallic Character/Nonmetal Reaction
Nonmetallic Character/Nonmetal Reaction increases as you move up and right.
Cation and Anions
Cations are the metals and anions are the nonmetals.
- Los Alamos National Laboratory's Chemistry Division Dec 11, 2003 periodic table of elements -retrieve date 2-5-09
- Lackman, Jon 2005 "Elemental" -retrieve date 2-6-09
- Lenntech Periodic table history 1998 -retreive date 2/6/09
- Julian Trubin
- atomic structues: metals, nonmetals, semimetals. -retreave date 2-5-09
- David D. Hsu. 1996 chemicool -retrieve date 2-5-09
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