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How does one determine the ionic charge of a transition element when it is in an ionic...

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ceeee | Student, College Freshman | (Level 1) Honors

Posted October 8, 2011 at 4:13 AM via web

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How does one determine the ionic charge of a transition element when it is in an ionic compound?

for example: in the problem:

Fe+2 + MnO4 --------> Fe+3 + Mn+2

I know that the charge of Fe in the first half is plus 2.

and in the second part Fe is +3 and Mn is +2

but how do i figure out what the charge of MnO4 is?

can you also provide other examples of how to find the charges so that i can fully understand how to do this. thanks a lot!!

1 Answer | Add Yours

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mwmovr40 | College Teacher | (Level 1) Associate Educator

Posted October 9, 2011 at 5:20 AM (Answer #1)

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Determining the electric charge of transition elements a priory can be very challenging.  However, if a transition element is part of an ionic compound it is usually possible to determine the charge of the cation (transition metal in this case) from the charge of the anion.

For ionic compounds the sum of the charges of the cations and ions must add to zero.  So, we simply need to determine the charge of the anion to determine the charge of the cation.  For example:

MnO4  Oxygen is a representative element in group VIA (or 16) which means it will normally form a 2- charge.  If there are 4 oxygen atoms in the compound, there must be a total of 8- charge for the anions.  Therefore the manganese must have a 8+ in order to provide a neutral compound.

FeCl3  Chlorine is a representative element in group VIIA (17) which means it will have a 1- charge.  Three chlorines means the anion has a total of 3-, therefore the iron must have a 3+ charge.

Fe2O3 (rust) has 3 oxygens for a total of 6-.  Therefore the iron must be a 3+ to create a neutral compound.

 

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