Editing Group 4 element (section)

===Physical===
The trends in group 4 follow those of the other early d-block groups and reflect the addition of a filled f-shell into the core in passing from the fifth to the sixth period. All the stable members of the group are silvery [[refractory metal]]s, though impurities of [[carbon]], [[nitrogen]], and oxygen make them brittle.<ref name=Greenwood956>Greenwood and Earnshaw, pp. 956–8</ref> They all crystallize in the [[hexagonal close-packed]] structure at room temperature,<ref name=Greenwood946>Greenwood and Earnshaw, pp. 946–8</ref> and rutherfordium is expected to do the same.<ref name=hcp>{{cite journal|doi=10.1103/PhysRevB.84.113104|title=First-principles calculation of the structural stability of 6d transition metals|year=2011|last1=Östlin|first1=A.|last2=Vitos|first2=L.|journal=Physical Review B|volume=84|issue=11|page=113104|bibcode=2011PhRvB..84k3104O }}</ref> At high temperatures, titanium, zirconium, and hafnium transform to a [[body-centered cubic]] structure. While they are better conductors of heat and electricity than their group 3 predecessors, they are still poor compared to most metals. This, along with the higher melting and boiling points, and enthalpies of fusion, vaporization, and atomization, reflects the extra d electron available for metallic bonding.<ref name=Greenwood946/>

The table below is a summary of the key physical properties of the group 4 elements. The four question-marked values are extrapolated.<ref name=Haire>{{cite book| title=The Chemistry of the Actinide and Transactinide Elements| editor1-last=Morss|editor2-first=Norman M.| editor2-last=Edelstein| editor3-last=Fuger|editor3-first=Jean| last1=Hoffman|first1=Darleane C. |last2=Lee |first2=Diana M. |last3=Pershina |first3=Valeria |chapter=Transactinides and the future elements| publisher= [[Springer Science+Business Media]]| year=2006| isbn=1-4020-3555-1| location=Dordrecht, The Netherlands| edition=3rd| ref=CITEREFHaire2006}}</ref>
{| class="wikitable centered" style="text-align:center;"
|+Properties of the group 4 elements| Properties of the group 4 elements
! Name
! Ti, [[titanium]]
! Zr, [[zirconium]]
! Hf, [[hafnium]]
! Rf, [[rutherfordium]]
|-
| style="background:lightgrey; text-align:left;"|[[Melting point]]
| 1941 K (1668&nbsp;°C) || 2130 K (1857&nbsp;°C) || 2506 K (2233&nbsp;°C) || 2400 K (2100&nbsp;°C)?
|-
| style="background:lightgrey; text-align:left;"|[[Boiling point]]
| 3560 K (3287&nbsp;°C) || 4682 K (4409&nbsp;°C) || 4876 K (4603&nbsp;°C) || 5800 K (5500&nbsp;°C)?
|-
| style="background:lightgrey; text-align:left;"|[[Density]]
| 4.507&nbsp;g·cm<sup>−3</sup> || 6.511&nbsp;g·cm<sup>−3</sup> || 13.31&nbsp;g·cm<sup>−3</sup> || 17&nbsp;g·cm<sup>−3</sup>?
|-
| style="background:lightgrey; text-align:left;"|Appearance
| silver metallic || silver white || silver gray|| ?
|-
| style="background:lightgrey; text-align:left;"|[[Atomic radius]]
| 140 pm || 155 pm || 155 pm || 150 pm?
|}
====Titanium====
{{transcluded section|Titanium}}
{{#section:Titanium|properties}}
====Zirconium====
{{transcluded section|Zirconium}}
{{#section:Zirconium|properties}}

====Hafnium====
{{transcluded section|Hafnium}}
{{#section:Hafnium|properties}}
====Rutherfordium====
{{transcluded section|Rutherfordium}}
{{#section:Rutherfordium|properties}}