# Titanium trichloride?

1. Nov 26, 2004

### Dual Op Amp

I have gone to www.webelements.com and have looked at a substance known as titanium trichloride. The electron structure is odd, a D orbital has only one electron. This doesn't make sense, the D orbital isn't filled, and the atom should be unstable. Can someone help.

2. Nov 27, 2004

### Staff: Mentor

Electron configuration of Ti is

$$1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^2\,4s^2$$

Ionization potentials 1) 6.83 eV, 2) 13.6 eV, 3) 27.6 eV, 4) 44.66 eV. One can see the relatively large difference between 3rd and 4th potentials. The difference between the 3rd and 4th valence states for Zr for instance is ~ 9.2 eV, and not surprisingly Zr forms compounds in the tetravalent state.

It is not surprising that Ti forms di- and tetra-valent compounds, however it may surprise some that it does form tri-valent compounds, and one of the most useful is TiCl3. However the compound is very reactive with air and water.

Some caution is needed - "Because of its sensitivity toward oxygen and water, anhydrous titanium trichloride should always be handled under an inert atmosphere. The submitters report that titanium trichloride in bottles that have been opened and resealed undergoes a slow deterioration that causes erratic results . . . . This decomposition is frequently detectable by the evolution of white fumes from the titanium trichloride during transfer. If a number of small-scale reactions are to be performed, the use of a Schlenk tube is advisable to extend the useful life of the titanium trichloride."

3. Nov 27, 2004

### Dual Op Amp

That doesn't make sense, it would either fill the entire fourth shell, or delete it totally. I don't understand. An atom is more stable when the entire valence shell is filled, so titanium should try to either fill or empty the third and fourth shell, right?

4. Nov 27, 2004

### Gokul43201

Staff Emeritus
You'll find this wackiness in most compounds involving transition metals.

The energy levels with d-orbitals (within Eg and t2g) being so close to each other allows d-block elements (transition metals) to exhibit multiple valencies. So, while +4 (or[Ar]) is the preferred oxidation state of Ti, the +2 and +3 states are not uncommon. Geometric (steric, or other) factors are also responsible for determining the stablest composition.

5. Nov 27, 2004

### Lyuokdea

Usually the 4s energy level has a slightly lower energy associated with it than the 3d enerfgy level. Thus electrons will fall into the 4s before the 3d, the only common exception to this is that if the atom can form a half full or completely full d shell by moving one electron from the 4s orbital to the 3d orbital, then it will usually do that. For instance, Chromium will have a
[Ar]3d^5 4s^1 configuration instead of [Ar]3d^4 4s^2

~Lyuokdea

6. Nov 27, 2004

### Staff: Mentor

An atom is more stable when the entire valence shell is filled, so titanium should try to either fill or empty the third and fourth shell, right?

Yes that is right, and that is why one will find bi-valent or tetravalent compounds, and the tetravalent compounds are much certainly more stable. For examples, TiO2, a common white pigment in paints, is very stable.

Both dihalides and trihalides are produced by reducing their respective tetrahalide. Remember, TiCl3 is very reactive, readily reacting with air and moisture, and is an effective reducing agent. TiCl2 is even more reactive.

7. Nov 29, 2004

### Dual Op Amp

I'm still confused, it would have to bond with a whole bunch of atoms in order to fill or empty it's valence shell.

8. Nov 30, 2004

### Dual Op Amp

Okay, now I'm really confused.

9. Dec 1, 2004

### Staff: Mentor

Here is a reference:

http://www.millenniumchem.com/Produ...ings/r_TiO2+Fundamentals/Titanium+Ores_EN.htm

In nature, Ti tends to form oxides with other metals, and its most natural state is Ti(4+).

In the industrial chemical realm, one can 'force' Ti to 2+ and 3+ states depending on the stoichiometry, so one can make TiCl2, TiCl3 and TiCl4. Of these, TiCl4 is most stable. As previously states, TiCl3 is more reactive (i.e. less stable than TiCl4) and TiCl2 is even more reactive than TiCl3.

Also remember that the halides, of which F and Cl are the most reactive, draw electrons from metals, particularly those from the left side of the periodic table. So Ti certainly would not fill the 'outer shell'.

10. Dec 1, 2004

### Dual Op Amp

But either way it doesn't add up to a complete valence shell, so it should try to find a way to add up to a complete valence shell. But, it doesn't. The entire third shell should be completely filled or emptied, but that doesn't happen. I'm just not getting this, I must of missed something.

11. Dec 1, 2004

### Gokul43201

Staff Emeritus
What you're missing is that while TiCl3 exists, it is not very stable - because of the partially filled outer shell.

"But it doesn't" ? No...it does. That's what it means to say that it is very reactive...it tries to reach a stabler configuration "if it can". But it exists in something like a metastable state, which, if slightly perturbed will fall into a more stable state.

12. Dec 1, 2004

### Dual Op Amp

So, that titanium is not completely stable. So, why doesn't it bond with another atom to get even more stable?

13. Dec 1, 2004

### Dual Op Amp

The titanium atom is trying to fill up the entire valence shell, the only way to do that is to either fill the entire third shell or completely empty the D,P, and S orbitals in the third shell, but it doesn't do that. In order to do that, it would have to bond with fourteen atoms!!!

14. Dec 1, 2004

### Staff: Mentor

Metals very rarely exist in the environment in their 'free' or elemental state. Most metal is founds in compounds of metal oxides, metal sulphides, carbonates, silicates, sulphates, etc.

Mankind devotes enormous quantities of energy to refine and purify metals. The we develop special alloys (e.g. stainless steels, superalloys, etc) and compounds (e.g. TiCl3) for specific purposes. These alloys and compounds do not exist in nature.

TiCl3 is manufactured in a very controlled environment, which is believe involves the reduction of TiCl4. At the moment, I cannot find a process in the public domain.

It must stored in a sealed container which is inert so that it will not react with air or water (moisture).

In the presence of O and the halides, Ti gives up electrons, so it is 'emptying' its valence electrons. Its most stable state is to give up 4 electrons 3d2 and 4s2. The particular valence depends on the chemical environment and the availability or lack of anionic species that will allow it to settle to its most stable form.

TiCl2 is a 'vigorous' reducing agent, and TiCl3 is an 'effective' reducing agent, i.e. TiCl3 is slightly less reactive than TiCl2.

15. Dec 2, 2004

### Dual Op Amp

Yes, this has gone past titanium trichloride. As I read www.webelements.com , I found more elements that the valence shells don't add up. The titanium would empty the 3D and 4S shell, but what about the 3P and the 3S shells? In order to become stable, it would need to empty those.

16. Dec 3, 2004

### Dual Op Amp

When I look online at the valence orbitals of titanium, I find that the valence orbitals are a 4S^2 and a 3D^2, but what about the valence orbitals 3P^6 and 3S^2?

17. Dec 3, 2004

### Staff: Mentor

Valence orbitals 3P6 and 3S2 have much higher binding energies (ionization potentials). If those electrons where available, one would find TiO6 (using 3P6, 3S2, 4S2, 3D2), but we see such a compound.

In theory, one could see TiCl12, but only 6 Cl could fit around a Ti atom and the other 6 would be excluded. However, Ti4 is the most stable form of the Ti chlorides.

Valence electrons are the outer most electrons - think of element Groups from the Periodic Table.

Bonds form to minimize energy. Think of heat of formation.

18. Dec 3, 2004

### Dual Op Amp

So, you're saying that Titanium bonds with the most stable configuration there is, besides filling the entire shell, because it can't fit all of the desired atom onto itself?

19. Dec 4, 2004

### Dual Op Amp

Is that what he's saying?

20. Dec 5, 2004