Achieve W9 Q#2

[Alexis Shen 2G]

Hi everyone, I'm having a lot of trouble determining the oxidation state for the central metal atom in [HgI3]-. I thought it would be -1, but that is incorrect. Thanks in advance!

[MiaRosati3L]

Hi there! The oxidation state of the metal is determined based on the charges of each ligand and the overall charge of the coordination compound. For example, in [Cr(H2O)4Cl2]Br, the coordination sphere (in brackets) has a charge of 1+ to balance the bromide ion. The water ligands are neutral, and the chloride ligands are anionic with a charge of 1− each. To determine the oxidation state of the metal, we set the overall charge equal to the sum of the ligands and the metal: +1 = −2 + x, so the oxidation state (x) is equal to 3+. Hopefully this example can help you to figure out the problem from Achieve!

[Alexis Shen 2G]

Hi there! The oxidation state of the metal is determined based on the charges of each ligand and the overall charge of the coordination compound. For example, in [Cr(H2O)4Cl2]Br, the coordination sphere (in brackets) has a charge of 1+ to balance the bromide ion. The water ligands are neutral, and the chloride ligands are anionic with a charge of 1− each. To determine the oxidation state of the metal, we set the overall charge equal to the sum of the ligands and the metal: +1 = −2 + x, so the oxidation state (x) is equal to 3+. Hopefully this example can help you to figure out the problem from Achieve!

How did you know the water ligands are neutral and the chloride ligands are -1? Also, how do I know which ones are water and which ones are chloride?

[Sarthika Chimmula 3H]

The overall charge of the compound is -1. Therefore the sum of all of the charges of the elements that make up the compound should also be -1. Because there are three iodine atoms and the charge of iodine is -1, this means 3 iodine atoms will have a total charge of -3. Therefore, the Hg transition metal ion should have a charge of positive 2 because -3+2=-1.

[Alexis Shen 2G]

The overall charge of the compound is -1. Therefore the sum of all of the charges of the elements that make up the compound should also be -1. Because there are three iodine atoms and the charge of iodine is -1, this means 3 iodine atoms will have a total charge of -3. Therefore, the Hg transition metal ion should have a charge of positive 2 because -3+2=-1.

Oh ok, that kind of makes sense! Does that mean that everything inside the brackets are ions? Sorry, this seems like a really basic question, but this topic confuses me quite a bit.

[Jacqueline Vargas 3L]

Hi!

To find the oxidation state of the central atom in [Hg I3]-

1.) Make the central atom a variable, such as X.
2.) Find the charge of the ligands.
3.) Set your variable and the total charge of the ligands equal to the overall charge of the compound.
4.) Solve

So
central atom + amount of ligand (charge of ligand) = overall charge
Hg + 3 ( I- ) = -1
x + 3 (-1) = -1
x - 3 = -1
x = 2

Hope that helps!

[Olivia Ghorai 1J]

Hi,

When you are trying to determine the oxidation number of an element within a molecule/compound, you need to look at the overall charge of the compound and use clues to determine the individual oxidation numbers. With HgI3, we know that it has an overall charge of -1. We also know that the charge of I is -1, and there are 3 of them so it is -3. The charge of Hg would need to make the overall charge -1, so it is +2.

[MiaRosati3L]

Hi there! The oxidation state of the metal is determined based on the charges of each ligand and the overall charge of the coordination compound. For example, in [Cr(H2O)4Cl2]Br, the coordination sphere (in brackets) has a charge of 1+ to balance the bromide ion. The water ligands are neutral, and the chloride ligands are anionic with a charge of 1− each. To determine the oxidation state of the metal, we set the overall charge equal to the sum of the ligands and the metal: +1 = −2 + x, so the oxidation state (x) is equal to 3+. Hopefully this example can help you to figure out the problem from Achieve!

How did you know the water ligands are neutral and the chloride ligands are -1? Also, how do I know which ones are water and which ones are chloride?

Great question! It helps to first draw out the compound's Lewis structure. Chromium is the central atom in the compound because it's the transition metal of this particular coordination complex. Everything else inside of the brackets is a part of the coordination sphere, so it's bonded to the central chromium atom. H2O is water, and there's four of those since it says (H2O)4, while there's one molecule of Cl2, which is chloride. I'm not sure how to insert images into posts, so I would suggest Googling "[Cr(H2O)4Cl2]Br Lewis structure" to see what it should look like.

As for the charges, we can use the rules for oxidation numbers (more info on these rules here: https://socratic.org/chemistry/electroc ... on-numbers). The essential rules are:
1) The oxidation number of a halogen in a compound is -1 unless it is with a more electronegative element.
2) The sum of the oxidation numbers of all atoms in a neutral compound is 0.
3) The sum of the oxidation numbers of all atoms in an ion equals charge on the ion.

Per Rule 1, the oxidation number of Cl is -1. Write the oxidation number above the Cl in the formula.
The two Cl atoms together have a total oxidation number of -2. Write this number below the Cl atom.
Per Rule 2, the sum of all the oxidation numbers in H2O must be 0, so then put zeroes above and below the formula for water.
Per Rule 3, the sum of all the oxidation numbers equals +1. Let x = the oxidation number of Cr. Then x - 2 + 0 = 1, and x = 1 + 2 = 3.
There is only one Cr atom, so its oxidation number must be +3.

[MiaRosati3L]

The overall charge of the compound is -1. Therefore the sum of all of the charges of the elements that make up the compound should also be -1. Because there are three iodine atoms and the charge of iodine is -1, this means 3 iodine atoms will have a total charge of -3. Therefore, the Hg transition metal ion should have a charge of positive 2 because -3+2=-1.

Oh ok, that kind of makes sense! Does that mean that everything inside the brackets are ions? Sorry, this seems like a really basic question, but this topic confuses me quite a bit.

No worries, this content is really tricky! The stuff inside the brackets includes the transition metal cation, which appears first if you're reading from left to right, followed by a ligand or multiple ligands. Ligands that are attached to the central transition metal ion make up the coordination sphere. Ligands are molecules, atoms, or ions, by the way. So, in this example I3 (triiodide) is the only ligand and it is an anion composed of three iodine atoms.

[Alexis Shen 2G]

Hi there! The oxidation state of the metal is determined based on the charges of each ligand and the overall charge of the coordination compound. For example, in [Cr(H2O)4Cl2]Br, the coordination sphere (in brackets) has a charge of 1+ to balance the bromide ion. The water ligands are neutral, and the chloride ligands are anionic with a charge of 1− each. To determine the oxidation state of the metal, we set the overall charge equal to the sum of the ligands and the metal: +1 = −2 + x, so the oxidation state (x) is equal to 3+. Hopefully this example can help you to figure out the problem from Achieve!

How did you know the water ligands are neutral and the chloride ligands are -1? Also, how do I know which ones are water and which ones are chloride?

Great question! It helps to first draw out the compound's Lewis structure. Chromium is the central atom in the compound because it's the transition metal of this particular coordination complex. Everything else inside of the brackets is a part of the coordination sphere, so it's bonded to the central chromium atom. H2O is water, and there's four of those since it says (H2O)4, while there's one molecule of Cl2, which is chloride. I'm not sure how to insert images into posts, so I would suggest Googling "[Cr(H2O)4Cl2]Br Lewis structure" to see what it should look like.

As for the charges, we can use the rules for oxidation numbers (more info on these rules here: https://socratic.org/chemistry/electroc ... on-numbers). The essential rules are:
1) The oxidation number of a halogen in a compound is -1 unless it is with a more electronegative element.
2) The sum of the oxidation numbers of all atoms in a neutral compound is 0.
3) The sum of the oxidation numbers of all atoms in an ion equals charge on the ion.

Per Rule 1, the oxidation number of Cl is -1. Write the oxidation number above the Cl in the formula.
The two Cl atoms together have a total oxidation number of -2. Write this number below the Cl atom.
Per Rule 2, the sum of all the oxidation numbers in H2O must be 0, so then put zeroes above and below the formula for water.
Per Rule 3, the sum of all the oxidation numbers equals +1. Let x = the oxidation number of Cr. Then x - 2 + 0 = 1, and x = 1 + 2 = 3.
There is only one Cr atom, so its oxidation number must be +3.

Thank you for all of your replies! I also read the other one that isn't quoted here and that makes a lot of sense! I'm just a little confused about one thing you wrote here. What does rule 3 mean? Does it mean that the sum of all oxidation numbers needs to equal the oxidation number on the metal?

[MiaRosati3L]

How did you know the water ligands are neutral and the chloride ligands are -1? Also, how do I know which ones are water and which ones are chloride?

Great question! It helps to first draw out the compound's Lewis structure. Chromium is the central atom in the compound because it's the transition metal of this particular coordination complex. Everything else inside of the brackets is a part of the coordination sphere, so it's bonded to the central chromium atom. H2O is water, and there's four of those since it says (H2O)4, while there's one molecule of Cl2, which is chloride. I'm not sure how to insert images into posts, so I would suggest Googling "[Cr(H2O)4Cl2]Br Lewis structure" to see what it should look like.

As for the charges, we can use the rules for oxidation numbers (more info on these rules here: https://socratic.org/chemistry/electroc ... on-numbers). The essential rules are:
1) The oxidation number of a halogen in a compound is -1 unless it is with a more electronegative element.
2) The sum of the oxidation numbers of all atoms in a neutral compound is 0.
3) The sum of the oxidation numbers of all atoms in an ion equals charge on the ion.

Per Rule 1, the oxidation number of Cl is -1. Write the oxidation number above the Cl in the formula.
The two Cl atoms together have a total oxidation number of -2. Write this number below the Cl atom.
Per Rule 2, the sum of all the oxidation numbers in H2O must be 0, so then put zeroes above and below the formula for water.
Per Rule 3, the sum of all the oxidation numbers equals +1. Let x = the oxidation number of Cr. Then x - 2 + 0 = 1, and x = 1 + 2 = 3.
There is only one Cr atom, so its oxidation number must be +3.

Thank you for all of your replies! I also read the other one that isn't quoted here and that makes a lot of sense! I'm just a little confused about one thing you wrote here. What does rule 3 mean? Does it mean that the sum of all oxidation numbers needs to equal the oxidation number on the metal?

In reference to the third rule (which, in hindsight, I think I could've explained better), the algebraic sum of the respective oxidation numbers of the ligands and the transition metal in the coordination complex (everything in brackets) must be equal to the oxidation number of the atom/molecule/ion outside of the coordination complex (the thing not in brackets). So, for instance, if the ligands and transition metal combined have a total charge of -3, whatever is outside of the coordination sphere should have a charge of +3 to give a net charge of 0 (they should cancel each other out). In the example I gave, Cr has a +3 charge, the two Cl atoms have a -2 charge, H2O is 0, so the system has an overall +1 charge. This means that Br must have a -1 charge to match the +1 charge of the coordination complex.

Here's a video that might be able to explain this topic better than I can: https://www.youtube.com/watch?v=fS0X7afRz4Q

[Joelle Tran 1K]

The charge on Hg in [HgI3]^-1 should be +2. The charges on the surrounding atoms of I are -1 and there are 3 so -1*3 = -3. The overall charge of the compound is -1 and so the metal must be +2 to balance out the -3.

[Alexis Shen 2G]

Great question! It helps to first draw out the compound's Lewis structure. Chromium is the central atom in the compound because it's the transition metal of this particular coordination complex. Everything else inside of the brackets is a part of the coordination sphere, so it's bonded to the central chromium atom. H2O is water, and there's four of those since it says (H2O)4, while there's one molecule of Cl2, which is chloride. I'm not sure how to insert images into posts, so I would suggest Googling "[Cr(H2O)4Cl2]Br Lewis structure" to see what it should look like.

As for the charges, we can use the rules for oxidation numbers (more info on these rules here: https://socratic.org/chemistry/electroc ... on-numbers). The essential rules are:
1) The oxidation number of a halogen in a compound is -1 unless it is with a more electronegative element.
2) The sum of the oxidation numbers of all atoms in a neutral compound is 0.
3) The sum of the oxidation numbers of all atoms in an ion equals charge on the ion.

Per Rule 1, the oxidation number of Cl is -1. Write the oxidation number above the Cl in the formula.
The two Cl atoms together have a total oxidation number of -2. Write this number below the Cl atom.
Per Rule 2, the sum of all the oxidation numbers in H2O must be 0, so then put zeroes above and below the formula for water.
Per Rule 3, the sum of all the oxidation numbers equals +1. Let x = the oxidation number of Cr. Then x - 2 + 0 = 1, and x = 1 + 2 = 3.
There is only one Cr atom, so its oxidation number must be +3.

Thank you for all of your replies! I also read the other one that isn't quoted here and that makes a lot of sense! I'm just a little confused about one thing you wrote here. What does rule 3 mean? Does it mean that the sum of all oxidation numbers needs to equal the oxidation number on the metal?

In reference to the third rule (which, in hindsight, I think I could've explained better), the algebraic sum of the respective oxidation numbers of the ligands and the transition metal in the coordination complex (everything in brackets) must be equal to the oxidation number of the atom/molecule/ion outside of the coordination complex (the thing not in brackets). So, for instance, if the ligands and transition metal combined have a total charge of -3, whatever is outside of the coordination sphere should have a charge of +3 to give a net charge of 0 (they should cancel each other out). In the example I gave, Cr has a +3 charge, the two Cl atoms have a -2 charge, H2O is 0, so the system has an overall +1 charge. This means that Br must have a -1 charge to match the +1 charge of the coordination complex.

Here's a video that might be able to explain this topic better than I can: https://www.youtube.com/watch?v=fS0X7afRz4Q

Ohhhh, that makes way more sense! Thank you so much and you're really good at explaining, don't worry! I'm just slow at chemistry :P

[Crystal Ma 2J]

Hi,
It should be +2 since the charge on I is -1 and we have 3 atoms so that would be a charge of -3. The total charge is -1 so -3+2=-1 and therefore Hg should have a charge of +2

[Jonathan Liu 2I]

Since iodine has a charge of negative 1, and there are three iodine atoms, the metal ion will need to have a positive charge that would make it so the compound would have an overall charge of negative 1, therefore it would have a oxidation number of positive 2