View source for User:Double sharp/Halogen

{{noindex}}
{{Infobox periodic table group
| title       = Halogens
| group number= 17
| trivial name= halogens
| by element  = fluorine group
| CAS         = VIIA
| old IUPAC   = VIIB
| mark        = F,Cl,Br,I,At,Ts
| left        = [[Chalcogen|chalcogens]]
| right       = [[Noble gas|noble gases]]}}
{| class="floatright"
! colspan=2 style="text-align:left;" | ↓&nbsp;[[Period (periodic table)|Period]]
|-
! [[Period 2 element|2]]
| {{element cell image|9|Fluorine|F| |Gas|Halogen|Primordial|image=Liquid fluorine tighter crop.jpg|image caption=Liquid fluorine at cryogenic temperatures}}
|-
! [[Period 3 element|3]]
| {{element cell image|17|Chlorine|Cl| |Gas|Halogen|Primordial|image=Chlorine ampoule.jpg|image caption=Chlorine gas}}
|-
! [[Period 4 element|4]]
| {{element cell image|35|Bromine|Br| |Liquid|Halogen|Primordial|image=Bromine 25ml.jpg|image caption=Liquid bromine}}
|-
! [[Period 5 element|5]]
| {{element cell image|53|Iodine|I| |Solid|Halogen|Primordial|image=Iod kristall.jpg|image caption=Iodine crystal}}
|-
! [[Period 6 element|6]]
| {{element cell image|85|Astatine|At| |Solid|Halogen|From decay}}
|-
! [[Period 7 element|7]]
| {{element cell image|117|Tennessine|Ts| |Unknown phase|Halogen|Synthetic}}
|-
| colspan="2"|
----
''Legend''
{| style="text-align:center; border:0;margin: 0 auto"
|-
| style="border: {{element color|Primordial}}; background:{{Element color|table mark}}; padding:0 2px;" |[[primordial element]]
|-
| style="border: {{element color|from decay}}; background:{{Element color|table mark}};" |[[Trace radioisotope|element from decay]]
|-
| style="border:{{element color|Synthetic}}; background:{{Element color|table mark}};" | [[Synthetic element|Synthetic]]
|-
| Atomic number color:
|-
| <span style="color:{{element color|Solid}}">black=solid</span>, <span style="color:{{element color|Liquid}}">green=liquid</span>, <span style="color:{{element color|Gas}}">red=gas</span>
|}
|}

The '''halogens''' are a [[group (periodic table)|group]] (column) in the [[periodic table]] consisting of the [[chemical element]]s [[fluorine]] (F), [[chlorine]] (Cl), [[bromine]] (Br), [[iodine]] (I), [[astatine]] (At), and possibly also the synthetic element [[tennessine]] (Ts). This group lies in the [[p-block]] of the periodic table of elements as all halogens have seven [[valence electron]]s, arranged in the [[electron configuration]] ns<sup>2</sup>np<sup>5</sup>. Since all the halogens are one electron short of a full [[octet rule|octet]], they exhibit well-characterised [[homology (chemistry)|homologous]] behaviour and provide one of the the best examples of [[periodic trends|group trends]] in properties in the periodic table.

In their standard states, the halogens are all quite [[volatility (chemistry)|volatile]]

say something about diatomicity (sharing)

Oh dear I've gotten myself stuck into the astatine problem again, haven't I? I think I need to take care of occurrence in the first paragraph so I can mention that At is rare because it's so radioactive so a negligible amount accumulates from U decay (and Ts is even more ephemeral, but has no naturally occurring parent). Then we can sya that not much is known about it