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Predict the number of unpaired electrons in CoF6^3-. Explain  

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First we have to identify the charge of the cobalt ion in an octahedral complex `[CoF_6]^(3-)` .

`x + (-1 *6) = -3`

`x = -3 + 6`

`x = + 3 = Co^(3+)`

Looking at the periodic table we can see that the element cobalt has a configuration of `4s^2 3d^7` and the cobalt (III) ion would be `3d^6` .

For octahedral complexes, the crystal field splitting diagram will have its `e_g` orbitals above the `t_(2g)` orbitals and is affected by the ligand that is attached to the cobalt ion. 

F- is a weak ligand and therefore will have a high spin state. Consequently, the six electrons are distributed to each of the orbitals.

   __ __ `e_g`

__ __ __   `t_(2g)`


    `uarr`    `uarr`    
   ---  ---     `e_g`

`uarr darr`   `uarr`    `uarr`
---- ---  ---   `t_(2g)`

1 paired 

4 unpaired electrons

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