The group IV of the periodic table constitutes Titanium,Zirconium and Hafnium. These elements have strong tendency to exhibit the oxidation state of +4. The properties of titanium are different from zirconium and hafnium so the separation of a titanium from their mixture is comparatively easier. Moreover, due to the lanthanide contraction, the metallic radii of this elements do not differ.
| Properties | Ti | Zr | Hf |
|---|---|---|---|
| Atomic Number | 22 | 40 | 72 |
| Electronic Configuration | [Ar] 3d2 4s2 | [Kr] 4d2 5s2 | [Xe] 4f14 5d2 6s2 |
| Metallic radius (nm) | 0.147 | 0.160 | 0.158 |
| M4+ radius (nm) | 0.068 | 0.080 | 0.081 |
| I1 (kJ mol-1) | 658 | 670 | 530 |
| Density (g cm-3) | 4.54 | 6.53 | 13.3 |
| Melting Point (K) | 1950 | 2130 | 2470 |
These atoms possess two spin free electrons (d2)and hence they are paramagnetic whereas their M+4 ions are diamagnetic.They are silvery white, lustrous metals with high melting points and resistant to corrosion because of the formation of a protective oxide layer over the metal surface. They are also good conductors of electricity. Among them titanium is abundant in nature. They decompose steam on strong heating. They do not react with cold dilute acids but they dissolve in hot concentrated acids especially in the presence of F–.
Oxidation States
These elements exhibit the following oxidation states.
| Ti | +II | +III | +IV |
| Zr | +II | +III | +IV |
| Hf | - | +III | +IV |
Where the +4-oxidation state is the most stable. The elements with lower oxidation states acts as reducing agents. The M3+ (d1) compounds are paramagnetic and coloured.
Halides
The chlorides of these metal undergo reaction with anhydrous HF to form Tetra fluorides.
The tetra fluoride forms stable compounds
Cl2 gas is passed over their dioxides to form MCl4. TiCl4 is a colourless strong fuming liquid whereasZrCl4 and HfCl4 are solids which gets hydrolysed by water as follows:
The trihalides are oxidised to the +4-oxidation state by water. TiCl2 is formed by passing an electric discharge through a mixture of TiCl4(g) and H2(g).
Uses
Titanium is majorly used in aircraft industry for production of engines and frames of aircraft. In chemical processing and Marine equipment.
They form alloys with small quantities of aluminium and tin which has highest strength: weight ratio among the available engineering metals. Hence, it is used to make gas turbine engines.
Zirconium is used in some chemical industries instead of stainless steel because of its high corrosion resistance and it also forms a superconducting alloy with Nb.
It is also used for cladding uranium dioxide fuel rods in water cooled nuclear reactors.
Hf is used as control rods in nuclear submarines because of its high neutron absorbing capacity.
