Help:Periodic table classifications in the English Wikipedia
The periodic table orders the chemical elements, showing several patterns in chemical and physical properties. Some details are arbitrary: they can be changed depending on scientific argument without breaking the table's structural essence. Also, editorial choices can be made, such as the use of colors.
This page describes the choices that were made in this English Wikipedia (enwiki), when showing the periodic table. Some are made in scientific disputes (like positioning of hydrogen), some are editorial (like background colors for metalloids).
Not all topics the periodic table shows are straightforward and undisputed. Some are chosen by scientific arguments, in chemistry and physics. For example, the set of metalloids varies throughout literature. The set of metalloids this wiki uses is motivated in the article, while also describing other reasoned sets.
Apart from science, also editorial choices are made. For example, it is quite common to show the "18-column" format (with two extra rows below the main table), while the "32-column" form (the bottom rows put in their proper location) is showing exactly the same statements. Also, when elements are categorised as "noble gas", they have a key color (blue) which is a free editorial choice: being a noble gas does not enforce a particular color.
Periodic table
The basic periodic table in enwiki:
| Group | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hydrogen & alkali metals |
Alkaline earth metals | Triels | Tetrels | Pnictogens | Chalcogens | Halogens | Noble gases | ||||||||||||
| Period |
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| 2 | |||||||||||||||||||
| 3 | |||||||||||||||||||
| 4 | |||||||||||||||||||
| 5 | |||||||||||||||||||
| 6 | 
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| 7 | 
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- Ca: 40.078 — Abridged value (uncertainty omitted here)[2]
- Po: [209] — mass number of the most stable isotope
18-column and 32-column layout
These forms are only editorially (graphically) different, showing the same scientific statements.
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| 18-column layout | 32-column layout |
IUPAC names
When available, enwiki uses names as defined by IUPAC. This is especially true for elements names aluminium, sulfur, caesium (which have variant spellings). So even when article aluminium is written in US-English, the US-spelling "aluminum" is not used.
When IUPAC has not provided or sanctioned a name, a common or descriptive name is used (metalloids, post-transition metals).
Groups
Group names
Groups (columns in the periodic table) are numbered 1–18, following modern IUPAC guidelines. Earlier group naming systems (Roman numbers with an A- or B-suffix: VIA or VIB), and trivial group names like halogens, are described here
Group 3: Sc/Y/Lu/Lr
This enwiki shows group 3 being Sc/Y/Lu/Lr, based on a IUPAC provisional report of January 2021. The discussion was conducted here.
Periods
Extended periodic table
Currently, 118 elements have been discovered and named, number 118 being oganesson. This happens to fill the whole periodic table in 7 rows (periods). Heavier element (atomic number 119 and higher) are theoretically described, and start in period 8 (row 8). When these elements are placed in the periodic table, it is called an extended periodic table.
Categories
Category is the word this Wikipedia uses for classifications in the metal-metalloid-nonmetal range. There is not common word for it in the scientific world, and 'category' is not used for anything else.
Categorising
- Note: as of September 2017, an RfC is open to change nonmetal categories. See here.
The English Wikipedia categorises the elements in these categories:
- Metals
- Alkali metal
- Alkaline earth metal
- Lanthanide
- Actinide
- Transition metal
- Post-transition metal
- Metalloid
- Nonmetals
- Polyatomic nonmetal
- Diatomic nonmetal
- Noble gas
- Unknown chemical properties
- Category not known
The background colors are used as a legend, and are a local (English wiki) choice. Not all names are commonly used, and the inclusion may be arbitrary. For example, the list of metalloids varies between sources.
Category key colors
- Scheme per April 2018
Each category has its own background color for legend (key) purposes.
| Metal | Metalloid #cccc99 |
Nonmetal | unknown chemical properties #e8e8e8 | |||||||
| Alkali metal #ff9d9d |
Alkaline earth metal #ffdead |
Lanthanide #ffbfff |
Actinide #ff99cc |
Transition metal #ffc0c0 |
Post-transition metal #cccccc |
Reactive nonmetal #a1ffc3 |
Noble gas #c0ffff | |||
More categories
Per April 2018, "predicted" categories such as "superactinides" and "theoretically, an alkali metal" are abandoned and not used any more.
History of changes
"Polyatomic nonmetals", "diatomic nonmetals" abandoned, replaced by Reactive nonmetals (2018)
April 2018. 11 elements affected. The green color disappears, a new yellow color is used.
Group 12: a post-transition metals, not transition metals (August 2017)
Group 12 (zinc, cadmium, mercury, copernicium) are calssified post-transition metal (not transition metal).
Individual elements classification (April 2017)
April 2017: flerovium (Fl) recategorised as "unknown".
Astatine as a metalloid (August 2013)
Nonmetals: categories "polyatomic nonmetal" and "diatomic nonmetal" (August 2013)
Halogens: is a group, but not a category (August 2013)
See also
- ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–291. doi:10.1515/pac-2015-0305.
- ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.