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The periodiс table of the chemical elements (also, periodic table of the elements or just periodic table) is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.^[1]

The periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry, physics, biology, and engineering, especially chemical engineering. The current standard table contains 117 elements as of July 2009 (elements 1-116 and element 118).

Structure of the periodic table

The periodiс table of the chemical elements (also, periodic table of the elements or just periodic table) is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.^[2]

The periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry, physics, biology, and engineering, especially chemical engineering. The current standard table contains 117 elements as of July 2009 (elements 1-116 and element 118).

Structure of the periodic table

       Template loop detected: Periodic table (standard)

Other alternative periodic tables exist.

Some versions of the table show a dark stair-step line along the metalloids. Metals are to the left of the line and non-metals to the right.^[3]

The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus). Rows are arranged so that elements with similar properties fall into the same columns (groups or families). According to quantum mechanical theories of electron configuration within atoms, each row (period) in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.

In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers.

As of 2006, the table contains 117 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been produced artificially in particle accelerators. Elements 43 (technetium), 61 (promethium), 93 (neptunium) and 94 (plutonium) have no stable isotopes and were first discovered synthetically; however, they were later discovered in trace amounts on earth as products of natural radioactive decay processes.

The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons. For instance, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines the family, or group, to which 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 (the Aufbau principle):

Subshell:	S	G	F	D	P
Period
1	1s
2	2s				2p
3	3s				3p
4	4s			3d	4p
5	5s			4d	5p
6	6s		4f	5d	6p
7	7s		5f	6d	7p
8	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.

Note that as atomic number (i.e., charge on the atomic nucleus) increases, this leads to greater spin-orbit coupling between the nucleus and the electrons, reducing the validity of the quantum mechanical orbital approximation model, which considers each atomic orbital as a separate entity.

The elements ununbium, ununtrium, ununquadium, etc. are elements that have been discovered, but so far have not received a trivial name yet. There is a system for naming them temporarily.

Classification

Groups

A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the alkali metals, alkaline earth metals, halogens, pnictogens, chalcogens, and noble gases. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.

Periods

A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.

Blocks

File:800px-PTable.png

This diagram shows the periodic table blocks.

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.

Other

The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as transition metals, poor metals, and metalloids. Other informal groupings exist, such as the platinum group and the noble metals.

Periodicity of chemical properties

The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.

Periodic trends of groups

Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties. Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.

Periodic trends of periods

Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.

History

In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, non-metals, and earths, chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as being soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third.^[4] This became known as the Law of triads.^{[citation needed]} German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.^[4]

German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency. In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency.^[5]

English chemist John Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements: When listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music.^[6]^[7] This law of octaves, however, was ridiculed by his contemporaries.^[8]

Finally, in 1869 the Russian chemistry professor Dmitri Ivanovich Mendeleev and four months later the German Julius Lothar Meyer independently 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 neighbors 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.

Earlier attempts to list the elements to show the relationships between them (for example by Newlands) had usually involved putting them in order of atomic mass. Mendeleev's key insight in devising the periodic table was to lay out the elements to illustrate recurring ("periodic") chemical properties (even if this meant some of them were not in mass order), and to leave gaps for "missing" elements. Mendeleev used his table to predict the properties of these "missing elements", and many of them were indeed discovered and fit the predictions well.

With the development of theories of atomic structure (for instance by Henry Moseley) it became apparent that Mendeleev had listed the elements in order of increasing atomic number (i.e., the net amount of positive charge on the atomic nucleus). This sequence is nearly identical to that resulting from ascending atomic mass.

In order to illustrate recurring properties, Mendeleev began new rows in his table so that elements with similar properties fell into the same columns ("groups").

With the development of modern quantum mechanical theories of electron configuration within atoms, it became apparent that each row ("period") in the table corresponded to the filling of a quantum shell of electrons. In Mendeleev's original table, each period was the same length. Modern tables have progressively longer periods further down the table, and group the elements into s-, p-, d- and f-blocks to reflect our understanding of their electron configuration.

In the 1940s, research groups led by Edwin Mattison McMillan and Glenn T. Seaborg (see transuranium elements) identified the transuranic lanthanides and the actinides, which may be placed within the table, or below (as shown above).

Notes

^ IUPAC article on periodic table
^ IUPAC article on periodic table
^ Science Standards of Learning Curriculum Framework
^ ^a ^b Ball, p. 100
^ Ball, p. 101
^ Newlands, John A. R. (1864-08-20). "On Relations Among the Equivalents". Chemical News. 10: 94–95.
^ Newlands, John A. R. (1865-08-18). "On the Law of Octaves". Chemical News. 12: 83.
^ Bryson, Bill (2004). A Short History of Nearly Everything. London: Black Swan. pp. 141–142. ISBN 9780552151740.

References

Ball, Philip (2002). The Ingredients: A Guided Tour of the Elements. Oxford University Press. ISBN 0-19-284100-9.
Theodore L. Brown, H. Eugene LeMay, and Bruce E. Bursten (2005). Chemistry:The Central Science (10th ed.). Prentice Hall. ISBN 0-13-109686-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
Helmenstine, Marie (2007). "Trends in the Periodic Table". About, Inc. Retrieved 2007-01-27.

External links

UC Berkeley video lecture on the Periodic table
Interactive periodic table

Template:Link FL

Other alternative periodic tables exist.

Some versions of the table show a dark stair-step line along the metalloids. Metals are to the left of the line and non-metals to the right.^[1]

The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus). Rows are arranged so that elements with similar properties fall into the same columns (groups or families). According to quantum mechanical theories of electron configuration within atoms, each row (period) in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.

In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers.

As of 2006, the table contains 117 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been produced artificially in particle accelerators. Elements 43 (technetium), 61 (promethium), 93 (neptunium) and 94 (plutonium) have no stable isotopes and were first discovered synthetically; however, they were later discovered in trace amounts on earth as products of natural radioactive decay processes.

The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons. For instance, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines the family, or group, to which 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 (the Aufbau principle):

Subshell:	S	G	F	D	P
Period
1	1s
2	2s				2p
3	3s				3p
4	4s			3d	4p
5	5s			4d	5p
6	6s		4f	5d	6p
7	7s		5f	6d	7p
8	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.

Note that as atomic number (i.e., charge on the atomic nucleus) increases, this leads to greater spin-orbit coupling between the nucleus and the electrons, reducing the validity of the quantum mechanical orbital approximation model, which considers each atomic orbital as a separate entity.

The elements ununbium, ununtrium, ununquadium, etc. are elements that have been discovered, but so far have not received a trivial name yet. There is a system for naming them temporarily.

Classification

Groups

A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the alkali metals, alkaline earth metals, halogens, pnictogens, chalcogens, and noble gases. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.

Periods

A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.

Blocks

File:800px-PTable.png

This diagram shows the periodic table blocks.

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.

Other

The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as transition metals, poor metals, and metalloids. Other informal groupings exist, such as the platinum group and the noble metals.

Periodicity of chemical properties

The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.

Periodic trends of groups

Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties. Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.

Periodic trends of periods

Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.

History

In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, non-metals, and earths, chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as being soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third.^[2] This became known as the Law of triads.^{[citation needed]} German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.^[2]

German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency. In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency.^[3]

English chemist John Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements: When listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music.^[4]^[5] This law of octaves, however, was ridiculed by his contemporaries.^[6]

Finally, in 1869 the Russian chemistry professor Dmitri Ivanovich Mendeleev and four months later the German Julius Lothar Meyer independently 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 neighbors 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.

Earlier attempts to list the elements to show the relationships between them (for example by Newlands) had usually involved putting them in order of atomic mass. Mendeleev's key insight in devising the periodic table was to lay out the elements to illustrate recurring ("periodic") chemical properties (even if this meant some of them were not in mass order), and to leave gaps for "missing" elements. Mendeleev used his table to predict the properties of these "missing elements", and many of them were indeed discovered and fit the predictions well.

With the development of theories of atomic structure (for instance by Henry Moseley) it became apparent that Mendeleev had listed the elements in order of increasing atomic number (i.e., the net amount of positive charge on the atomic nucleus). This sequence is nearly identical to that resulting from ascending atomic mass.

In order to illustrate recurring properties, Mendeleev began new rows in his table so that elements with similar properties fell into the same columns ("groups").

With the development of modern quantum mechanical theories of electron configuration within atoms, it became apparent that each row ("period") in the table corresponded to the filling of a quantum shell of electrons. In Mendeleev's original table, each period was the same length. Modern tables have progressively longer periods further down the table, and group the elements into s-, p-, d- and f-blocks to reflect our understanding of their electron configuration.

In the 1940s, research groups led by Edwin Mattison McMillan and Glenn T. Seaborg (see transuranium elements) identified the transuranic lanthanides and the actinides, which may be placed within the table, or below (as shown above).

Notes

^ Science Standards of Learning Curriculum Framework
^ ^a ^b Ball, p. 100
^ Ball, p. 101
^ Newlands, John A. R. (1864-08-20). "On Relations Among the Equivalents". Chemical News. 10: 94–95.
^ Newlands, John A. R. (1865-08-18). "On the Law of Octaves". Chemical News. 12: 83.
^ Bryson, Bill (2004). A Short History of Nearly Everything. London: Black Swan. pp. 141–142. ISBN 9780552151740.

References

Ball, Philip (2002). The Ingredients: A Guided Tour of the Elements. Oxford University Press. ISBN 0-19-284100-9.
Theodore L. Brown, H. Eugene LeMay, and Bruce E. Bursten (2005). Chemistry:The Central Science (10th ed.). Prentice Hall. ISBN 0-13-109686-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
Helmenstine, Marie (2007). "Trends in the Periodic Table". About, Inc. Retrieved 2007-01-27.

External links

UC Berkeley video lecture on the Periodic table
Interactive periodic table

Template:Link FL

[1] IUPAC article on periodic table

[2] IUPAC article on periodic table

[3] Science Standards of Learning Curriculum Framework

[Ball100-4] Ball, p. 100

[5] Ball, p. 101

[6] Newlands, John A. R. (1864-08-20). "On Relations Among the Equivalents". Chemical News. 10: 94–95.

[7] Newlands, John A. R. (1865-08-18). "On the Law of Octaves". Chemical News. 12: 83.

[8] Bryson, Bill (2004). A Short History of Nearly Everything. London: Black Swan. pp. 141–142. ISBN 9780552151740.

[9] Science Standards of Learning Curriculum Framework

[Ball100-10] Ball, p. 100

[11] Ball, p. 101

[12] Newlands, John A. R. (1864-08-20). "On Relations Among the Equivalents". Chemical News. 10: 94–95.

[13] Newlands, John A. R. (1865-08-18). "On the Law of Octaves". Chemical News. 12: 83.

[14] Bryson, Bill (2004). A Short History of Nearly Everything. London: Black Swan. pp. 141–142. ISBN 9780552151740.

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[2]

[3]

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@@ Line 6: / Line 6: @@
 The periodic table is now ubiquitous within the academic discipline of [[chemistry]], providing an extremely useful framework to classify, systematize and compare all of the many different forms of [[chemical]] behavior. The table has found wide application in [[chemistry]], [[physics]], [[biology]], and [[engineering]], especially [[chemical engineering]]. The current standard table contains 117 elements as of July 2009 (elements [[hydrogen|1]]-[[ununhexium|116]] and element [[ununoctium|118]]).
-==Methods for displaying the periodic table==
+==Structure of the periodic table==
-===Standard periodic table{{anchor|Standard periodic table}}===
            <!--Code included from the [[Periodic table (standard)]] article:-->
         {{:periodic table (standard)|width:100ht:100%}}
-===Alternative versions (layout/view of the table)===
-*The [[Periodic table (wide)|wide table]] sets inline the f-block of [[lanthanide]]s and [[actinide]]s.
-*An alternate [http://www.tannerm.com/longform.htm wide table] sets Sc, Y, La, Ac in the same column.
-*The [[Periodic table (standard)|standard table]] (same as above) provides the basics.
-*A [[Periodic table (alternate)|vertical table]] scrolls down for narrow pages.
-*The [[Periodic table (big)|big table]] provides the basics and full element names.
-*The [[Periodic table (large version)|large table]] provides the above and [[atomic mass]]es.
-*The [[Periodic table (detailed)|detailed table]] provides a smaller version of the huge table.
-*The [[electronegativity|electronegativity table]] provides electronegativities.
-*[[Periodic table (electron configurations)|Electron configurations]]
-*[[Periodic table (metals and non-metals)|Metals and non-metals]]
-*The [[Periodic table (block)|blocks]] are shaded instead of series.
-*The [[Periodic table (valence)|valences]] are shaded instead of series.
 Other [[alternative periodic tables]] exist.
 Some versions of the table show a dark stair-step line along the metalloids. Metals are to the left of the line and non-metals to the right.<ref>[http://www.doe.virginia.gov/VDOE/Instruction/Science/ScienceCF-PS.doc Science Standards of Learning Curriculum Framework]</ref>
-==Arrangement==
 The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing [[atomic number]] (i.e., the number of [[proton]]s in the [[atomic nucleus]]). Rows are arranged so that elements with similar properties fall into the same columns (''groups'' or ''families''). According to [[quantum mechanics|quantum mechanical]] theories of [[electron]] configuration within atoms, each row (''period'') in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into ''s-'', ''p-'', ''d-'' and ''f-blocks'' to reflect their [[electron configuration]].
@@ Line 37: / Line 20: @@
 As of 2006, the table contains 117 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are [[synthetic elements]] that have been produced artificially in [[particle accelerators]]. Elements 43 (technetium), 61 (promethium), 93 (neptunium) and 94 (plutonium) have no stable isotopes and were first discovered synthetically; however, they were later discovered in trace amounts on earth as products of natural radioactive decay processes.
-==Periodicity of chemical properties==
-The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.
-===Groups and periods===
-{{Main|Group (periodic table)|Period (periodic table)}}
-* A '''group''' or '''family''' is a vertical column in the periodic table.
-Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the [[alkali metal]]s, [[alkaline earth metals]], [[halogen]]s, [[pnictogen]]s, [[chalcogen]]s, and [[noble gas]]es. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.
-* A '''period''' is a horizontal row in the periodic table.
-Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the [[d-block]] (or "[[transition metal]]s"), and especially for the [[f-block]], where the [[lanthanoids]] and [[actinoids]] form two substantial horizontal series of elements.
-====Periodic trends of groups====
-Modern [[quantum mechanics|quantum mechanical]] theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their [[electron_shell#Valence_shells|valence shell]], which is the most important factor in accounting for their similar properties.
-Elements in the same group also show patterns in their [[atomic radius]], [[ionization energy]], and [[electronegativity]]. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
-====Periodic trends of periods====
-[[Image:Ionization energies.png|thumb|300px|Periodic trend for [[ionization energy]]. Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.]]
-Elements in the same period show trends in [[atomic radius]], [[ionization energy]], [[electron affinity]], and [[electronegativity]]. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. [[Electron affinity]] also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.
-===Examples===
-====Noble gases====
-{{Main|Noble gas}}
-All the elements of Group 18, the [[noble gases]], have full valence shells. This means they do not need to react with other elements to attain a full shell, and are therefore much less reactive than other groups. [[Neon]] followed by [[helium]] are the most [[inert]] elements among noble gases, since reactivity, in this group, increases with the periods: it is possible to make heavy noble gases react since they have much larger electron shells. However, their reactivity remains very low in absolute terms.
-====Halogens====
-{{Main|Halogen}}
-In Group 17, known as the [[halogen]]s, elements are missing just one electron each to fill their shells. Therefore, in chemical reactions they tend to acquire electrons (the tendency to acquire electrons is called [[electronegativity]]). This property is most evident for [[fluorine]] (the most electronegative element of the whole table), and it diminishes with increasing period.
-As a result, all halogens form acids with hydrogen, such as [[hydrofluoric acid]], [[hydrochloric acid]], [[hydrobromic acid]] and [[hydroiodic acid]], all in the form ''HX''. Their [[acidity]] increases with higher period, for example, with regard to iodine and fluorine, since a large I<sup>−</sup> [[ion]] is more stable in solution than a small F<sup>−</sup>, there is less volume in which to disperse the charge.
-====Transition metals====
-{{Main|Transition metal}}
-For the [[transition metal]]s (Groups 3 to 12), horizontal trends across periods are often important as well as vertical trends down groups; the differences between groups adjacent are usually not dramatic. Transition metal reactions often involve coordinated species.
-====Lanthanoids and actinoids====
-{{Main|Lanthanoid|Actinoid}}
-The chemical properties of the [[lanthanoid]]s (elements 57–71) and the [[actinoid]]s (elements 89–103) are even more similar to each other than the [[transition metal]]s, and separating a mixture of these can be very difficult. This is important in the ''chemical'' purification of [[uranium]] concerning [[nuclear power]].
-==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, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of [[valence shell]] electrons determines the family, or group, to which the element belongs.
@@ Line 106: / Line 51: @@
 Note that as [[atomic number]] (i.e., charge on the [[atomic nucleus]]) increases, this leads to greater [[spin-orbit coupling]] between the nucleus and the electrons, reducing the validity of the quantum mechanical [[orbital approximation]] model, which considers each atomic orbital as a separate entity.
+The elements ununbium, ununtrium, ununquadium, etc. are elements that have been discovered, but so far have not received a [[trivial name]] yet. There is a [[Systematic element name|system]] for naming them temporarily.
+==Classification==
+===Groups===
+{{Main|Group (periodic table)}}
+ A ''group'' or ''family'' is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the [[alkali metal]]s, [[alkaline earth metals]], [[halogen]]s, [[pnictogen]]s, [[chalcogen]]s, and [[noble gas]]es. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.
+===Periods===
+{{Main|Period (periodic table)}}
+A ''period'' is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the [[d-block]] (or "[[transition metal]]s"), and especially for the [[f-block]], where the [[lanthanoids]] and [[actinoids]] form two substantial horizontal series of elements.
+===Blocks===
+{{Main|Periodic table block}}
 [[Image:800px-PTable.png|thumb|This diagram shows the [[periodic table block]]s.]]
+Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as ''[[periodic table block]]s'', named according to the sub-shell in which the "last" electron resides, e.g., the ''s''-block, the ''p''-block, the ''d''-block, etc.
+===Other===
-Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as '''[[periodic table block]]s''', named according to the sub-shell in which the "last" electron resides, e.g., the ''s''-block, the ''p''-block, the ''d''-block, etc.
+The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as [[transition metal]]s, [[poor metal]]s, and [[metalloid]]s. Other informal groupings exist, such as the [[platinum group]] and the [[noble metals]].
+==Periodicity of chemical properties==
-The elements ununbium, ununtrium, ununquadium, etc. are elements that have been discovered, but so far have not received a [[trivial name]] yet. There is a [[Systematic element name|system]] for naming them temporarily.
+The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.
+===Periodic trends of groups===
+Modern [[quantum mechanics|quantum mechanical]] theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their [[electron_shell#Valence_shells|valence shell]], which is the most important factor in accounting for their similar properties.
+Elements in the same group also show patterns in their [[atomic radius]], [[ionization energy]], and [[electronegativity]]. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
+===Periodic trends of periods===
+[[Image:Ionization energies.png|thumb|300px|Periodic trend for [[ionization energy]]. Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.]]
+Elements in the same period show trends in [[atomic radius]], [[ionization energy]], [[electron affinity]], and [[electronegativity]]. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. [[Electron affinity]] also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.
 ==History==

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v t e Branches of chemistry
Glossary of chemical formulae List of biomolecules List of inorganic compounds Periodic table
Analytical	Calorimetry Characterization Chromatography GC HPLC Crystallography Electroanalytical methods Elemental analysis Instrumental chemistry Mass spectrometry EI ICP MALDI Separation process Spectroscopy IR Raman UV-Vis NMR Titration Wet chemistry
Theoretical	Computational chemistry Mathematical chemistry Molecular modelling Molecular mechanics Molecular dynamics Molecular geometry VSEPR theory Quantum chemistry
Physical	Chemical kinetics Chemical physics Molecular physics Chemical thermodynamics Cryochemistry Electrochemistry Spectroelectrochemistry Photoelectrochemistry Equilibrium chemistry Femtochemistry Interface and colloid science Micromeritics Mechanochemistry Microwave chemistry Photochemistry Sonochemistry Spectroscopy Spin chemistry Structural chemistry Surface science Thermochemistry
Inorganic	Ceramic chemistry Cluster chemistry Coordination chemistry Magnetochemistry Organometallic chemistry Organolanthanide chemistry Solid-state chemistry
Organic	Dynamic covalent chemistry Enantioselective synthesis Fullerene chemistry Organic reactions Organic synthesis Petrochemistry Physical organic chemistry Polymer chemistry Retrosynthetic analysis Stereochemistry Alkane stereochemistry Total synthesis / Semisynthesis
Biological	Biochemistry Molecular biology Cell biology Bioinorganic chemistry Bioorganic chemistry Bioorganometallic chemistry Biophysical chemistry Chemical biology Bioorthogonal chemistry Clinical chemistry Medicinal chemistry Pharmacology Neurochemistry
Interdisciplinarity	Nuclear chemistry Radiochemistry Radiation chemistry Actinide chemistry Cosmochemistry / Astrochemistry / Stellar chemistry Geochemistry Biogeochemistry Photogeochemistry Environmental chemistry Atmospheric chemistry Ocean chemistry Clay chemistry Carbochemistry Food chemistry Carbohydrate chemistry Food physical chemistry Agricultural chemistry Soil chemistry Chemistry education Amateur chemistry General chemistry Clandestine chemistry Forensic chemistry Forensic toxicology Post-mortem chemistry Nanochemistry Supramolecular chemistry Chemical synthesis Green chemistry Click chemistry Combinatorial chemistry Biosynthesis Chemical engineering Stoichiometry Materials science Metallurgy Ceramic engineering Polymer science
See also	History of chemistry Nobel Prize in Chemistry Timeline of chemistry of element discoveries "The central science" Chemical reaction Catalysis Chemical element Chemical compound Atom Molecule Ion Chemical substance Chemical bond Alchemy Quantum mechanics
Category Commons Portal WikiProject

Periodic table: Difference between revisions

Revision as of 21:39, 19 July 2009

Structure of the periodic table

Structure of the periodic table

Classification

Groups

Periods

Blocks

Other

Periodicity of chemical properties

Periodic trends of groups

Periodic trends of periods

History

See also

Notes

References

Further reading

External links

Classification

Groups

Periods

Blocks

Other

Periodicity of chemical properties

Periodic trends of groups

Periodic trends of periods

History

See also

Notes

References

Further reading

External links