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Basic Chemistry Concepts

Periodic Table

original periodic table, H2Te, H2Se, modern periodic table, modern table

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Periodic Table, table of the chemical elements arranged to illustrate patterns of recurring chemical and physical properties. Elements, such as oxygen, iron, and gold, are the most basic chemical substances and cannot be broken down by chemical reactions. All other substances are formed from combinations of elements. The periodic table provides a means of arranging all the known elements and even those yet to be discovered.

Although all elements differ from one another, some show similarities that allow scientists to categorize them. Around 1870, Russian chemist Dmitry Mendeleyev used these similarities to construct the original periodic table. Since that time, newly discovered elements have been added and the tableís layout has changed; however, the modern periodic table conveys essentially the same information as the one that Mendeleyev created. In the modern table, elements with similar properties fall into columns called groups or families. Group 1 of the periodic table, for example, contains a number of soft metals, all of which react vigorously with water to form hydrogen gas.

Uses of the Periodic Table

The periodic table is an important tool for scientists and students studying the chemical elements. If a person knows the main properties of each of the groups in the periodic table and how chemical properties vary within a group, he or she can predict the properties of any particular element with a reasonable degree of confidence. For example, if a student needs to know the properties of francium, she can predict that it, like other elements of group 1, will be a soft metal and will react even more vigorously with water than the elements above it. If another student wants to predict what compounds tellurium will form in combination with hydrogen, he can guess that the two elements will form H2Te because the other elements in telluriumís group form similar hydrogen compounds: H2O, H2S, and H2Se.


Scerri, Eric

Visiting Assistant Professor, Department of Chemistry and Biochemistry, University of California, Los Angeles.

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