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Encyclopedia > Period (periodic table)

In the periodic table of the elements, a 'period' is a horizontal row of the table. For a diagram of the periodic table, see standard periodic table below. ... The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ...


The elements are laid out in a series rows so that those with similar properties line up in vertical columns: this reflects the periodic recurrence of similar properties as atomic weight increases. ...


Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, electron shells are filled in roughly this order. The filling of each shell corresponds to a row in the table. Fig. ... [[Image:Valence shell 011 Sodiumup of one or more electron subshells, or sublevels, which have two or more orbitals with the same angular momentum quantum number l. ... It has been suggested that List of elements by atomic number be merged into this article or section. ...

 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s 5g 6f 7d 8p ... 

Hence the structure of the periodic table. Since the valence electrons determine chemical properties, those tend to be similar within periodic table groups. In chemistry, valence electrons are the electrons contained in the valence shell of an atom, and which are likely to participate in a chemical reaction through bonding with other atoms or molecules. ... A periodic table group is a vertical column in the periodic table of the chemical elements. ...


Elements adjacent to one another within a group have similar physical properties, despite their significant differences in mass. Elements adjacent to one another within a period have similar mass but different properties.


  Results from FactBites:
 
Chemistry: WebElements Periodic Table (426 words)
The periodic "law" of chemistry recognises that many properties of the chemical elements are periodic functions of their atomic number (the number of protons within the element's atomic nucleus).
The periodic table is an arrangement of the chemical elements ordered by atomic number in columns (groups) and rows (periods) presented so as to emphasize their periodic properties.
The relative merits of various other periodic table organisations is still the subject of debate.
Periodic Table - Printer-friendly - MSN Encarta (1146 words)
Periodic Table, table of the chemical elements arranged to illustrate patterns of recurring chemical and physical properties.
The periodic table has been published in various shapes and sizes, but the most commonly used modern form begins with a column of group 1 metals on the left-hand side, followed by a column of group 2 alkaline earth metals.
His version of the table was the first to accommodate all the known elements and also successfully predicted the existence of several elements that had not yet been discovered.
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