A little bit confusion about transition metal stuff and redox reaction

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co2mymail
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Hi , guys . i am having some difficulty to understand the redox half equation and transition metal
First of all , why red ox reaction never show a full molecule for transtion metal . For example . We say Potassium Dichromate Kr2Cr2O7 2- I am guessing that because the metal Kr will disassociate in the solution and form Kr+ and Cr2O7 2- .
However why transition metal doesn't behave the same ? Why in half equation , we need to write Chromium with oxygen by not by its own . ( Fe2+ can have it's own ion )
I am having some problem to decide what should i write in a half equation .
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Science_Girl
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I think it depends on the metal. For Scottish exams, we get a data book telling us this kind of thing, don't know about rest of UK.
What is the half equation you are writing, if you don't mind?
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Ben :)
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Transition metals don't behave the same because they are covalent molecules (the ligands form coordinate bonds with them) whereas Potassium Dichromate is ionic so will completely dissociate into the potassium ion and dichromate ion! You can have Chromium in many stable oxidation states so you can have Cr on its own (Cr2O7 ^2- / CrO4 ^- / Cr ^ 3+)
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co2mymail
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I was hoping there is a list like which transition metal bond to which element = convanet and in what cases they are in ionic .
I understand that anhydrous transition metal are convanent and when they are dissolve in water they become ionic and seperate out .
I was guessing that it is a difference in electronegativity the dipole in the compound , that's why the partially negative oxygen in water kind of attract to it and break the compound .
This is really confussssing

Somebody please helpppppppppppppppppp
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charco
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(Original post by co2mymail)
I was hoping there is a list like which transition metal bond to which element = convanet and in what cases they are in ionic .
I understand that anhydrous transition metal are convanent and when they are dissolve in water they become ionic and seperate out .
I was guessing that it is a difference in electronegativity the dipole in the compound , that's why the partially negative oxygen in water kind of attract to it and break the compound .
This is really confussssing

Somebody please helpppppppppppppppppp
C-O-V-A-L-E-N-T

It seems like you are rather mixed up with your concepts.

Normal metal ions are attracted to water molecules because of their polarity, but we don't consider that the bonding is any other than electrostatic attraction.

However, transition metal ions have available 'd' orbitals which allow them to accept electron pairs from water molecules (and other molecules or ions) to form (what is called) complex ions.

These usually involve six particles attached covalently to the central transition metal ion in an octahedral arrangement, although other configurations also occur (tetrahedral, square planar, both 4-coordinate for example).

The complex transition metal ion then behaves like any other ion in that it forms ionic compounds.

In solution the species is invariably the hexaaqua complex ion, eg:

[Fe(H2O)6]2+
[Fe(H2O)6]3+

The attached particles are called ligands (from the Latin, ligere = to link)
They may be easily replaced by other ligands (labile) or could form very strong bonds to the TM.

[Cu(H2O)6]2+ + 4Cl- --> [CuCl4]2- + 6H2O

This equation shows the ligand replacement reaction that occurs when copper sulfate solution (i.e. a solution containing hexaaqua copper(II) ions) reacts with concentrated hydrochloric acid (i.e. a solution containing a high concentration of chloride ions) and undergoes ligand replacement to form tetrachlorocuprate(II) ions.

There is plenty more chemistry involving transition metal ions, but this is the bare bones.
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