Editing Group 4 element (section)

===Chemical===

{| class="wikitable" style="float:right; font-size:95%;white-space:nowrap;"
|+
! colspan=4 | [[Electron configuration]]s of the group 4 elements
|-
! {{abbr|1=''Z''|2=Atomic number}} !! Element !! Electrons per [[Electron shell|shell]] !! Electron configuration
|-
| style="text-align:right" | 22 || Ti, titanium || {{mono|2, 8, 10, &nbsp;2}}    || {{mono|1=[Ar] &nbsp;&nbsp;<sup>&nbsp;&nbsp;</sup> 3d<sup>2</sup> 4s<sup>2</sup>}}
|-
| style="text-align:right" | 40 || Zr, zirconium   || {{mono|2, 8, 18, 10, &nbsp;2}}|| {{mono|1=[Kr] &nbsp;&nbsp;<sup>&nbsp;&nbsp;</sup> 4d<sup>2</sup> 5s<sup>2</sup>}}
|-
| style="text-align:right" | 72 || Hf, hafnium || {{mono|2, 8, 18, 32, 10, &nbsp;2}}  || {{mono|1=[Xe] 4f<sup>14</sup> 5d<sup>2</sup> 6s<sup>2</sup>}}
|-
| style="text-align:right" | 104 || Rf, rutherfordium || {{mono|2, 8, 18, 32, 32, 10, 2}} || {{mono|1=[Rn] 5f<sup>14</sup> 6d<sup>2</sup> 7s<sup>2</sup>}}
|}
Like other groups, the members of this family show patterns in their electron configurations, especially the outermost shells, resulting in trends in chemical behavior. Most of the chemistry has been observed only for the first three members of the group; chemical properties of rutherfordium are not well-characterized, but what is known and predicted matches its position as a heavier homolog of hafnium.<ref>{{cite journal | doi=10.1524/ract.2005.93.9-10.519 | title=Chemical studies on rutherfordium (Rf) at JAERI | date=2005 | last1=Nagame | first1=Y. | journal=Radiochimica Acta | volume=93 | issue=9–10_2005 | page=519 | url=http://wwwsoc.nii.ac.jp/jnrs/paper/JN62/jn6202.pdf | last2=Tsukada | first2=K. | last3=Asai | first3=M. | last4=Toyoshima | first4=A. | last5=Akiyama | first5=K. | last6=Ishii | first6=Y. | last7=Kaneko-Sato | first7=T. | last8=Hirata | first8=M. | last9=Nishinaka | first9=I. | last10=Ichikawa | first10=S. | last11=Haba | first11=H. | last12=Enomoto | first12=Shuichi | s2cid=96299943 | display-authors=1 | url-status=dead | archive-url=https://web.archive.org/web/20080528125634/http://wwwsoc.nii.ac.jp/jnrs/paper/JN62/jn6202.pdf | archive-date=2008-05-28 }}</ref>

Titanium, zirconium, and hafnium are reactive metals, but this is masked in the bulk form because they form a dense oxide layer that sticks to the metal and reforms even if removed. As such, the bulk metals are very resistant to chemical attack; most aqueous acids have no effect unless heated, and aqueous alkalis have no effect even when hot. Oxidizing acids such as [[nitric acid]]s indeed tend to reduce reactivity as they induce the formation of this oxide layer. The exception is [[hydrofluoric acid]], as it forms soluble fluoro complexes of the metals. When finely divided, their reactivity shows as they become [[pyrophoricity|pyrophoric]], directly reacting with [[oxygen]] and [[hydrogen]], and even [[nitrogen]] in the case of titanium. All three are fairly electropositive, although less so than their predecessors in [[group 3 element|group 3]].<ref name=Greenwood958>Greenwood and Earnshaw, pp. 958–61</ref> The oxides [[Titanium dioxide|TiO<sub>2</sub>]], [[Zirconium dioxide|ZrO<sub>2</sub>]] and [[Hafnium(IV) oxide|HfO<sub>2</sub>]] are white solids with high melting points and unreactive against most acids.<ref name="Holl">{{cite book|publisher = Walter de Gruyter|year = 1985|edition = 91–100|pages=1056–1057|isbn = 3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first1 = Arnold F.|last1 = Holleman|last2= Wiberg|first2=Egon|last3=Wiberg|first3=Nils|language = de}}</ref>

The chemistry of group 4 elements is dominated by the group oxidation state. Zirconium and hafnium are in particular extremely similar, with the most salient differences being physical rather than chemical (melting and boiling points of compounds and their solubility in solvents).<ref name=Holl/> This is an effect of the [[lanthanide contraction]]: the expected increase of atomic radius from the 4d to the 5d elements is wiped out by the insertion of the 4f elements before. Titanium, being smaller, is distinct from these two: its oxide is less basic than those of zirconium and hafnium, and its aqueous chemistry is more hydrolyzed.<ref name=Greenwood958/> Rutherfordium should have a still more basic oxide than zirconium and hafnium.<ref name=primefan>[http://www.primefan.ru/stuff/chem/front2019.png Periodic table poster] by A. V. Kulsha and T. A. Kolevich</ref>

The chemistry of all three is dominated by the +4 oxidation state, though this is too high to be well-described as totally ionic. Low oxidation states are not well-represented for zirconium and hafnium<ref name=Greenwood958/> (and should be even less well-represented for rutherfordium);<ref name=primefan/> the +3 oxidation state of zirconium and hafnium reduces water. For titanium, this oxidation state is merely easily oxidised, forming a violet Ti<sup>3+</sup> aqua cation in solution. The elements have a significant coordination chemistry: zirconium and hafnium are large enough to readily support the coordination number of 8. All three metals however form weak sigma bonds to carbon and because they have few d electrons, [[pi backbonding]] is not very effective either.<ref name=Greenwood958/>