Roman numerals

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EMurphy_2L
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Roman numerals

Postby EMurphy_2L » Mon Nov 25, 2019 3:13 pm

does the Roman numeral indicate the charge of the molecule or the charge of the metal in the coordination compound??

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Re: Roman numerals

Postby Chem_Mod » Mon Nov 25, 2019 3:15 pm

the charge of the central metal cation

Sebastian Lee 1L
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Re: Roman numerals

Postby Sebastian Lee 1L » Mon Nov 25, 2019 3:19 pm

The roman numeral indicates the positive charge of the transition metal cation. This notation is often used since transition metals can take on multiple oxidation states. For example, to distinguish Fe2+ and Fe3+ you would write Iron (II) or Iron (III).

If we have the coordination compound [Co (NH3)5 SO4]+ you can figure out that since the only charged ligand is sulfate (-2) and the overall charge is +1, then the Cobalt must have an oxidation number/charge of +3. You would then write the name as Pentaamine sulfato cobalt (III).

BeylemZ-1B
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Re: Roman numerals

Postby BeylemZ-1B » Mon Nov 25, 2019 3:30 pm

Sebastian Lee 1H wrote:The roman numeral indicates the positive charge of the transition metal cation. This notation is often used since transition metals can take on multiple oxidation states. For example, to distinguish Fe2+ and Fe3+ you would write Iron (II) or Iron (III).

If we have the coordination compound [Co (NH3)5 SO4]+ you can figure out that since the only charged ligand is sulfate (-2) and the overall charge is +1, then the Cobalt must have an oxidation number/charge of +3. You would then write the name as Pentaamine sulfato cobalt (III).


Why is it that transition metals are able to take on different charges?

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Re: Roman numerals

Postby Sebastian Lee 1L » Mon Nov 25, 2019 3:46 pm

BeylemZ-4A wrote:
Sebastian Lee 1H wrote:The roman numeral indicates the positive charge of the transition metal cation. This notation is often used since transition metals can take on multiple oxidation states. For example, to distinguish Fe2+ and Fe3+ you would write Iron (II) or Iron (III).

If we have the coordination compound [Co (NH3)5 SO4]+ you can figure out that since the only charged ligand is sulfate (-2) and the overall charge is +1, then the Cobalt must have an oxidation number/charge of +3. You would then write the name as Pentaamine sulfato cobalt (III).


Why is it that transition metals are able to take on different charges?


I'm not exactly sure why but I think it has to do with the electron configuration of the transition metals and their energies to gain/lose electrons. Typically, nonmetal p-block elements will have a specific negative oxidation number because they want a certain number of electrons to reach a stable octet. Adding on more electrons past an octet requires a lot more energy. For example, Cl will always be -1 because it has a high electron affinity for one electron but it won't get anymore past that.

Similarly, s-block metals will have a specific positive oxidation number because they can easily get rid of one or two electrons to gain a stable valence shell. Getting rid of more electrons past the stable octet will require energy. Na is always +1 because it will lose its extra 3s electron but not more.

However, with the transition metals, there are also electrons in the d-orbitals. So when you form an ion with a transition metal, you first get rid of the s-orbital electrons but then you can keep getting rid of other d-orbital electrons with a similar amount of energy. It isn't energetically unfavorable to gain a more positive charge since removing a d-electron doesn't take that much more energy. In the case of Fe3+, you would first get rid of the two 4s orbital electrons and then one 3d electron. Since the energies of the 4s and 3d subshells are so close to each other, it's easy to get rid of that extra 3d electron.


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