The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements first created in 1869 by Russian chemist Dmitri Mendeleev. The modern periodic table is arranged so that elements in each column of the table have the same number of valence electrons and therefore usually exhibit similar chemical properties. Each element is listed by its atomic number and element symbol; many versions of the table also include the element's atomic mass and its abbreviated electron configuration. As of 2005, the table contains 116 chemical elements whose discoveries have been confirmed. 94 are found naturally on Earth, and the rest have been produced artificially in laboratories.

The elements were originally arranged by atomic mass. Mendeleev shuffled cards with the elements' names and properties until he found a pattern. In 1913, Henry Moseley rearranged the table according to atomic number so that many chemical properties followed a regular pattern across the table. Mendeleev's and Moseley's development of the periodic table was one of the greatest achievements in modern chemistry. Chemists were able to quantitatively explain the behavior of the elements, and to predict the existence of yet undiscovered ones.

Groups

A group, also known as a family, is a vertical column in the periodic table of the elements. There are 18 groups or families in the standard periodic table. Elements in a group have similar configurations of their valence shell electrons, which gives them similar properties. Representative elements are elements in the periodic table that are designated with an A (IA through VIIIA, as discussed below).

Group numbers

There are three systems of group numbers; one using Hindu-Arabic numerals (1, 2, ... 18), another using Roman numerals (I, II, ... VIII), and one using a combination of Roman numerals and Latin letters (IA, IIA, IB, ... VIIIA). The Roman numeral names are the original traditional names of the groups; the Arabic numeral names are a newer naming scheme recommended by the International Union of Pure and Applied Chemistry (IUPAC). The IUPAC scheme was developed to replace both older Roman numeral systems as they confusingly used the same names to mean different things.

Standard periodic table

¹Actinides and lanthanides are collectively known as "Rare Earth Metals".

²Alkali metals, alkaline earth metals, transition metals, actinides, lanthanides, and poor metals are all collectively known as "Metals".

³Halogens and noble gases are also non-metals.

State at standard temperature and pressure

• those with atomic number in red are gases
• those with atomic number in blue are liquids
• those with atomic number in black are solid

Natural occurrence

• those with solid borders have isotopes that are older than the Earth (Primordial elements)
• those with dashed borders naturally arise from decay of other chemical elements and have no isotopes older than the earth
• those with dotted borders are made artificially (Synthetic elements)
• those without borders have not been discovered yet

Other methods for displaying the chemical elements

• The standard table (same as above) provides the basics.
• A vertical table for improved readability in web browsers.
• The big table provides the basics and full element names.
• The huge table provides the basics plus full element names and atomic masses.
• A table with an inline F-block inserts the Lanthanides and Actinides back into the table.
• Electron Configurations
• Metals and Non Metals
• Periodic table filled by blocks
• Table in Chinese
• List of elements by name
• List of elements by symbol
• List of elements by atomic number
• List of elements by boiling point
• List of elements by melting point
• List of elements by density
• List of elements by atomic mass
• List of elements by electronegativity

Other alternative periodic tables exist.

Periodicity of chemical properties

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, or energy level, have similar mass but different properties.

For example, very near to nitrogen (N) in the second period of the chart are carbon (C) and oxygen (O). Despite their similarities in mass (only a few atomic mass units), they have extremely different properties, as can be seen by looking at their allotropes: diatomic oxygen is a gas that supports burning, diatomic nitrogen is a gas that does not support burning, while carbon is a solid which can be burned. Diamonds which are a form of crystallized carbon can also burn. In the group known as the halogens, the element chlorine (Cl) falls between fluorine (F) and bromine (Br).

Despite their dramatic differences in mass, their allotropes have very similar properties. They are all highly corrosive. Chlorine and fluorine are gases, while bromine is a very low-boiling liquid. Chlorine and bromine are brightly colored, whereas fluorine is not.

Explanation of the structure of the periodic table

The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons. For instance, all atoms whose four valence electrons are found on the p shell will behave similarly, regardless of which energy level that last p shell is on. The shell in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines which family, or group, the element belongs.

The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order:

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 table. Since the outermost electrons determine chemical properties, those with the same number of valence electrons are grouped together.

Progressing through a group from lightest element to heaviest element, the outer-shell electrons (those most readily accessible for participation in chemical reactions) are all in the same type of orbital, with a similar shape, but with increasingly higher energy and average distance from the nucleus. For instance, the outer-shell (or "valence") electrons of the first group, headed by hydrogen all have one electron in an s orbital. In hydrogen, that s orbital is in the lowest possible energy state of any atom, the first-shell orbital (and represented by hydrogen's position in the first period of the table). In francium, the heaviest element of the group, the outer-shell electron is in the seventh-shell orbital, significantly further out on average from the nucleus than those electrons filling all the shells below it in energy. As another example, both carbon and lead have four electrons in their outer shell orbitals.

Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, named according to the sub-shell in which the "last" electron resides, e.g. the s-block, the p-block, the d-block, etc.

History

Main article: History of the periodic table

The original table was created without a knowledge of the inner structure of atoms: if one orders the elements by atomic mass, and then plots certain other properties against atomic mass, one sees an undulation or periodicity to these properties as a function of atomic mass. The first to recognize these regularities was the German chemist Johann Wolfgang Döbereiner who, in 1829, noticed a number of triads of similar elements:

This was followed by the English chemist John Newlands, who noticed in 1865 that the elements of similar type recurred at intervals of eight, which he likened to the octaves of music, though his law of octaves was ridiculed by his contemporaries. Finally, in 1869, the German Julius Lothar Meyer and the Russian chemistry professor Dmitri Ivanovich Mendeleev almost simultaneously developed the first periodic table, arranging the elements by mass. However, Mendeleev plotted a few elements out of strict mass sequence in order to make a better match to the properties of their neighbours in the table, corrected mistakes in the values of several atomic masses, and predicted the existence and properties of a few new elements in the empty cells of his table. Mendeleev was later vindicated by the discovery of the electronic structure of the elements in the late 19th and early 20th century.

In the 1940s Glenn T. Seaborg identified the transuranic lanthanides and the actinides, which may be placed within the table, or below (as shown above).

Further resources

• [1] Scerri, E.R., references to several scholarly articles by this author.
• Mazurs, E.G., "Graphical Representations of the Periodic System During One Hundred Years". University of Alabama Press, Alabama. 1974.
• Bouma, J., "An Application-Oriented Periodic Table of the Elements". J. Chem. Ed., 66 741 (1989).

See also

• Atomic electron configuration table
• Isotope table (complete)
• Isotope table (divided)
• Discoveries of the chemical elements
• Abundance of the chemical elements
• Tom Lehrer's song The Elements
• IUPAC's systematic element names
• Cosmochemical Periodic Table of the Elements in the Solar System
• Table of chemical elements

External links

• "Periodic table (professional edition)". WebElements.
• The IUPAC periodic table
• "Visual Periodic Table". ChemSoc.org.
• Counterman, Craig, "Periodic Table of the Elements : For each of many properties a separate periodic table and a graph showing the relation with the atomic number". MIT Course 3.091.
• Heilman, Chris, "The Pictorial Periodic Table". (Includes alternate styles: Stowe, Benfey, Zmaczynski, Giguere, Tarantola, Filling, Mendeleev)
• "Periodic table". Los Alamos National Laboratory's Chemistry Division.
• Dayah, Michael, "Periodic Table". Large full-color scalable text-only rendering.
• The periodic table for magnetic resonance.

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