Editing Extended periodic table (section)

====Elements 167 to 172====
The next six elements on the periodic table are expected to be the last main-group elements in their period,<ref name="PT172"/> and are likely to be similar to the 5p elements [[indium]] through [[xenon]].<ref name=primefan/> In elements 167 to 172, the 9p<sub>1/2</sub> and 8p<sub>3/2</sub> shells will be filled. Their energy [[eigenvalue]]s are so close together that they behave as one combined p-subshell, similar to the non-relativistic 2p and 3p subshells. Thus, the [[inert-pair effect]] does not occur and the most common oxidation states of elements 167 to 170 are expected to be +3, +4, +5, and +6, respectively. Element 171 (unseptunium) is expected to show some similarities to the [[halogen]]s, showing various oxidation states ranging from −1 to +7, although its physical properties are expected to be closer to that of a metal. Its electron affinity is expected to be 3.0&nbsp;[[electronvolt|eV]], allowing it to form H171, analogous to a [[hydrogen halide]]. The 171<sup>−</sup> ion is expected to be a [[HSAB|soft base]], comparable to [[iodide]] (I<sup>−</sup>). Element 172 (unseptbium) is expected to be a [[noble gas]] with chemical behaviour similar to that of xenon, as their ionization energies should be very similar (Xe, 1170.4&nbsp;kJ/mol; element 172, 1090&nbsp;kJ/mol). The only main difference between them is that element 172, unlike xenon, is expected to be a [[liquid]] or a [[solid]] at [[standard temperature and pressure]] due to its much higher atomic weight.<ref name="Fricke"/> Unseptbium is expected to be a strong [[Lewis acid]], forming fluorides and oxides, similarly to its lighter congener xenon.<ref name="BFricke"/>

Because of some analogy of elements 165–172 to periods 2 and 3, Fricke et al. considered them to form a ninth period of the periodic table, while the eighth period was taken by them to end at the noble metal element 164. This ninth period would be similar to the second and third period in having no transition metals.<ref name="BFricke"/> That being said, the analogy is incomplete for elements 165 and 166; although they do start a new s-shell (9s), this is above a d-shell, making them chemically more similar to groups 11 and 12.<ref name=actrev/>

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:{| class="wikitable"
|+ Some predicted properties of elements 167–172<br/>The metallic or covalent radii and densities are first approximations.<ref name="Fricke"/><ref name=Haire/><ref name="BFricke"/>
! Property
! 167
! 168
! 169
! 170
! 171
! 172
|-
! [[Standard atomic weight]]
| [485]
| [489]
| [493]
| [496]
| [500]
| [504]
|-
! [[Periodic table group|Group]]
| [[boron group|13]]
| [[carbon group|14]]
| [[pnictogen|15]]
| [[chalcogen|16]]
| [[halogen|17]]
| [[noble gas|18]]
|-
! Valence [[electron configuration]]
| 9s<sup>2</sup> 9p<sup>1</sup>
| 9s<sup>2</sup> 9p<sup>2</sup>
| 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>1</sup>
| 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>2</sup>
| 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>3</sup>
| 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>4</sup>
|-
! Stable [[oxidation state]]s
| '''3'''
| '''4'''
| '''5'''
| '''6'''
| '''−1''', '''3''', '''7'''
| '''0''', '''4''', '''6''', '''8'''
|-
! First [[ionization energy]]
| 620 kJ/mol
| 720 kJ/mol
| 800 kJ/mol
| 890 kJ/mol
| 984 kJ/mol
| 1090 kJ/mol
|-
! [[Metallic radius|Metallic]] or [[covalent radius]]
| 190 pm
| 180 pm
| 175 pm
| 170 pm
| 165 pm
| 220 pm
|-
! [[Density]]
| 17 g/cm<sup>3</sup>
| 19 g/cm<sup>3</sup>
| 18 g/cm<sup>3</sup>
| 17 g/cm<sup>3</sup>
| 16 g/cm<sup>3</sup>
| 9 g/cm<sup>3</sup>
|}
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