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Elements are the most basic substances. They make up everything in the universe from the oxygen we breathe to the water we drink and the food we eat. Everything we see and touch is made of one or more elements. Currently there are over 100 elements that have been identified by scientists. These elements are listed in a periodic table in order of atomic number.
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The periodic table is arranged in rows and columns according to certain characteristics of each element. Each row is called a period. Elements are not necessarily placed next to each other in a row, which creates a kind of flat U shape to the table. Each period contains elements that have the same number of atomic orbitals. The first row has the elements that have only one electron orbital. The second row, or period, has elements with two electron orbitals. This pattern continues through all seven rows of the table.
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The columns of the periodic table are called groups. The elements in each column have the same number of electrons in their outer shell, so they have similar bonding capabilities. The elements in the second column have two electrons in their outer shell and so on across the table. Counting from left to right will help indicate how many electrons in the outer shell any given element contains. The transitional elements do not completely follow this rule, but it is still useful as a general guideline.
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Letters and Numbers
The periodic table uses letters to indicate each element. Many elements have very long names that simply would not fit onto the table so a letter or pair of letters is used. Often it is the first letter of the name of the element, such as H for Hydrogen. When more than one element begins with the same letter the first two letters may be used, as in He for Helium and Hs for Hassium. Occasionally letters are chosen because they come from the Latin word such as using Fe for Iron. The Latin word for Iron is Ferrum.
Periodic tables may vary in their detail so there may be more than one number listed on the table. The number at the top should be sequential from 1 to 117 and is the atomic number of the element. Some tables may also list the atomic weight under the letter symbol for the element.
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Colors are occasionally used to help group elements between columns and rows. An example may be grouping alkali metals, non-metals, transitional metals, alkali earth metals, rare earth metals, halogens and rare gases. Many of these groups cross rows and columns, yet share some of the same characteristics. A key should be provided for the specific periodic table being reviewed if colors are used.
The arrangement of the elements on the table can help students understand how elements are likely to react with each other. Chemists and scientists around the world use the periodic table and are still working to discover new elements