Editing Period 6 element (section)

==f-block elements (lanthanides)==
{{main|Lanthanides}}
The '''lanthanide''' or '''lanthanoid''' ([[Chemical nomenclature|IUPAC nomenclature]])<ref>The current [[IUPAC]] recommendation is that the name ''lanthanoid'' be used rather than ''lanthanide'', as the suffix "-ide" is preferred for negative [[ion]]s whereas the suffix "-oid" indicates similarity to one of the members of the containing family of elements. However, ''lanthanide'' is still favored in most (~90%) scientific articles and is currently adopted on Wikipedia. In the older literature, the name "lanthanon" was often used.</ref> series comprises the fifteen [[metal]]lic [[chemical element]]s with [[atomic number]]s 57 through 71, from [[lanthanum]] through [[lutetium]].<ref name="Gray"/>{{rp|240}}<ref>[http://www.britannica.com.ph/chemistry/lanthanide-369725.html Lanthanide] {{webarchive|url=https://web.archive.org/web/20110911062241/http://www.britannica.com.ph/chemistry/lanthanide-369725.html |date=2011-09-11 }}, Encyclopædia Britannica on-line</ref><ref name="Holden2004">{{cite journal|author1=Holden, Norman E.|author2=Coplen, Tyler|name-list-style=amp|date=January–February 2004|journal=Chemistry International|title=The Periodic Table of the Elements|publisher=IUPAC|volume=26|issue=1|page=8|url=http://www.iupac.org/publications/ci/2004/2601/2_holden.html|access-date=March 23, 2010|archive-url=https://web.archive.org/web/20040217100116/http://www.iupac.org/publications/ci/2004/2601/2_holden.html|archive-date=February 17, 2004|url-status=dead}}</ref> These fifteen elements, along with the chemically similar elements [[scandium]] and [[yttrium]], are often collectively known as the '''[[rare-earth elements]].'''

The informal chemical symbol '''Ln''' is used in general discussions of lanthanide chemistry. All but one of the lanthanides are [[f-block]] elements, corresponding to the filling of the 4f [[electron shell]]; [[lanthanum]], a [[d-block]] element, is also generally considered to be a lanthanide due to its chemical similarities with the other fourteen. All lanthanide elements form trivalent cations, Ln<sup>3+</sup>, whose chemistry is largely determined by the [[ionic radius]], which decreases steadily from lanthanum to lutetium.

{| class="wikitable" style="background:#ffe; font-size:95%;"
![[Chemical element]]!![[Lanthanum|La]]!![[Cerium|Ce]]!![[praseodymium|Pr]]!![[neodymium|Nd]]!![[promethium|Pm]]!![[samarium|Sm]]!![[europium|Eu]]!![[gadolinium|Gd]]!![[terbium|Tb]]!![[dysprosium|Dy]]!![[holmium|Ho]]!![[erbium|Er]]!![[thulium|Tm]]!![[ytterbium|Yb]]!![[lutetium|Lu]]
|-
| [[Atomic number]]
|57||58||59||60||61||62||63||64||65||66||67||68||69||70||71
|-
|Image|| [[File:Lanthanum-2.jpg|50px]]||[[File:Cerium2.jpg|50px]]||[[File:Praseodymium.jpg|50px]]||[[File:Neodymium2.jpg|50px]]||||[[File:Samarium-2.jpg|50px]]||[[File:Europium.jpg|50px]]||[[File:Gadolinium-4.jpg|50px]]||[[File:Terbium-2.jpg|50px]]||[[File:Dy chips.jpg|50px]]||[[File:Holmium2.jpg|50px]]||[[File:Erbium-crop.jpg|50px]]||[[File:Thulium sublimed dendritic and 1cm3 cube.jpg|50px]]||[[File:Ytterbium-3.jpg|50px]]||[[File:Lutetium sublimed dendritic and 1cm3 cube.jpg|50px]]
|-
|Density (g/cm<sup>3</sup>)
|6.162 ||6.770 ||6.77 ||7.01 ||7.26 ||7.52 ||5.244 ||7.90 ||8.23 ||8.540 ||8.79 ||9.066 ||9.32 ||6.90 ||9.841
|-
|Melting point (°C)
|920 ||795 ||935 ||1024 ||1042 ||1072 ||826 ||1312 ||1356 ||1407 ||1461 ||1529 ||1545 ||824 ||1652
|-
| Atomic [[electron configuration]]*||'''5d<sup>1</sup>'''||4f<sup>1</sup>'''5d<sup>1</sup>'''||4f<sup>3</sup>|| 4f<sup>4</sup>|| 4f<sup>5</sup>||4f<sup>6</sup>||4f<sup>7</sup>|| 4f<sup>7</sup>'''5d<sup>1</sup>'''||4f<sup>9</sup>||4f<sup>10</sup>||4f<sup>11</sup>||4f<sup>12</sup>||4f<sup>13</sup>||4f<sup>14</sup>||4f<sup>14</sup>'''5d<sup>1</sup>'''
|-
| Ln<sup>3+</sup> electron configuration*<ref>{{cite book|author=Walter Koechner |title=Solid-state laser engineering |url=https://books.google.com/books?id=RK3jK0XWjdMC&pg=PA47 |access-date=15 January 2012 |year=2006 |publisher=Springer |isbn=978-0-387-29094-2|pages=47–}}</ref>||4f<sup>0</sup><ref>[http://www.chemistryexplained.com/Kr-Ma/Lanthanum.html Lanthanum – Chemistry Encyclopedia – reaction, water, elements, metal, gas, name, atom]. Chemistryexplained.com. Retrieved on 2012-01-15.</ref> || 4f<sup>1</sup>||4f<sup>2</sup>|| 4f<sup>3</sup>|| 4f<sup>4</sup>||4f<sup>5</sup>||4f<sup>6</sup>|| 4f<sup>7</sup>||4f<sup>8</sup>|| 4f<sup>9</sup>|| 4f<sup>10</sup>||4f<sup>11</sup>||4f<sup>12</sup>|| 4f<sup>13</sup>||
4f<sup>14</sup>
|-
| Ln<sup>3+</sup> radius ([[picometer|pm]])<ref name=Greenwood>{{Greenwood&Earnshaw|page=1233}}</ref> || 103 || 102 || 99|| 98.3|| 97|| 95.8|| 94.7|| 93.8|| 92.3|| 91.2|| 90.1|| 89||88|| 86.8|| 86.1
|}
*Between initial [Xe] and final 6s<sup>2</sup> electronic shells

The lanthanide elements are the group of elements with [[atomic number]] increasing from 57 (lanthanum) to 71 (lutetium). They are termed lanthanide because the lighter elements in the series are chemically similar to [[lanthanum]]. Strictly speaking, both lanthanum and lutetium have been labeled as [[group 3 element]]s, because they both have a single valence electron in the d shell. However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.

In presentations of the [[periodic table]], the [[lanthanides]] and the [[actinides]] are customarily shown as two additional rows below the main body of the table,<ref name="Gray" /> with placeholders or else a selected single element of each series (either [[lanthanum]] or [[lutetium]], and either [[actinium]] or [[lawrencium]], respectively) shown in a single cell of the main table, between [[barium]] and [[hafnium]], and [[radium]] and [[rutherfordium]], respectively. This convention is entirely a matter of [[aesthetics]] and formatting practicality; a rarely used [[Periodic table (detailed cells)#32-column layout|wide-formatted periodic table]] inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).