27. Transition Metals
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in this video, we're going to take a look at the concept of coordination complexes. Now we're going to say that the most prevalent feature of transition metal chemistry is the formation of coordination complexes or compounds. Now these structures are composed of a complex ion that is bonded or connected to ions or molecules called Liggins in order to maintain the overall neutrality of the compound, A counter ion is used. Alright, so if we take a look here at this example, we have nickel bonded to four ammonia molecules and then we have two chloride ions outside of the brackets. This thing overall together is our coordination complex. Now our coordination complex, you can think of it as just a more complicated ionic compound. Remember an ionic compound is composed of two things. It's composed of a positive ion called a cat ion and a negative ion called an an ion. So taking this logic, let's highlight this part here in yellow since it's in a in a bracket. It's altogether and outside the bracket we have these two chlorine. So what's in the bracket that represents our complex ion? What's outside the bracket is our counter ion. So outside the bracket we have two chlorine is which are really two chloride ions. So they are our counter ions. Now, where did this to come from? That too? Came from my complex ion portion. So it's still together as an eye four NH 3's to positive. This is my complex ion. Now we can go a little bit further and break the complex ion further into its components. So we're gonna say that this complex ion is composed of, What for ammonia molecules, we use the term molecules because ammonia is neutral and they represent our Liggins. So remember Liggins could either be neutral or they could have a charge. They could either be neutral or negative. So examples of a neutral ligand is ammonia, but you could also have water as another example of a neutral Ligon Liggins can also be negative. So examples of negative Liggins, you could have cyanide ion, you could have a Z ion, you could even have another halogen as a ligand. So those would be negative. Um And then if we think about it, the the legends here are four ammonia molecules, they're neutral. They don't provide any charge but yet are complex ion overall has a plus two charge. If it has an overall charge of plus two and the Liggins aren't contributing anything and that plus two charge has to be coming from the nickel, Nickel itself has to be plus two. So this would be our transition metal cat eye on. So again, our coordination complex is just a more complex ionic compound that can be broken down into its counter ion. And then it's complex ion traditionally when it comes to coordination complexes, what's in brackets is our complex ion, what's outside the brackets are are counter ions. Then you can further break down the complex ion into its ligand portions and its transition metal portion. Now we're gonna say connected to complex ion, complex ions, coordination complexes, all that stuff we have, what are called coordination coordination numbers. Now we're gonna say the coordination number is the number of Liggins bonded to the central metal cat ion. So your coordination number is how many of these Liggins are connected to my transition metal? In this case we said there were four Liggins connected to nickel two plus ion. Now we're going to say the most common coordination numbers are 24 and six Liggins attached to my transition metal. Can I on? There are other types um There are other numbers as well, but these are just the three most common ones that we see in organic chemistry. Alright, so now that we've gone over what a coordination complex is, how it's composed of a complex ion, counter ions, Liggins and transition metal, we'll take a look at the examples below. So I want you to click on to the next video and see how I approach the first example question dealing with our coordination complex given
Coordination Complexes Exercise 1
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So here it says correctly label all the components of the coordination complex. Now remember we say that traditionally when we have brackets what's inside the brackets represents our complex ion and what's outside our brackets represents our counter ions. In this example we have two sodium outside of the brackets. So they represent our counter ions, N. A. Is in group one, so its charges plus one. So we'd say we have two sodium ions that represent our counter ions. Then We have 10 with six. Corinne's. Alright, so where did this to come from? Well that too must have come from. The complex ion, sodium is positive in this case are complex ion now is negative. Remember our complex ion we said could be positive or negative. So here it would be S. N. C. L. Six still in brackets And the overall charge would be 2 -. So this represents our complex ion. Now we're gonna say, what is that complex ion further broken down into we're gonna say here that it is composed of six chloride ions. So these are our legans remember Liggins are what are directly connected to my transition metal. And if we think about it we have six chloride ions. So their overall contribution is a minus six in terms of charge. Right so six times negative one is negative six. And the overall charge here is -2 though. How is that possible? Well that would mean that tin has to be plus four in terms of charge. So plus four coming from the tin. The negative six coming from the six chlorine. Overall that gives us a negative two charge left over. So we're dealing with 10 4 ion. So this represents our transition metal cat. I'll So those would be all the components that we have here for our coordination complex. What's in the brackets can be seen as our complex ion. It can be either positive or negative, depending on what counter ions are used here. What's outside the brackets is our sodium. Those are our counter ions. Then you can go further into the complex ion and see what's the transition metal ion used and what are the types of Liggins used within the complex ion? We see that we have a tin four ion and six chloride ion Liggins involved. Now that we've seen this example, click onto the next video and see if you can figure out the number of Liggins within the provided complex ion. Come back and see, does your answer match up with mine
Coordination Complexes Exercise 2
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for this one, it says determine the number of Liggins in the complex ion. Now remember the complex ion portion is the part that is within the brackets, That fluoride is a counter ion because it's outside the brackets. So fluoride in group seven, so its charges -1. So to have an overall neutral coordination complex, That means it has to be plus one. Okay, so that plus one in the negative one, cancel out and that's why the coordination complex overall is neutral. Now we're gonna say within this complex ion portion, we see that chromium is our transition metal and it's connected to what appears to be four water molecules And two bromide ions. So that is a total of six Liggins that are attached to my chromium ion. So that would be our answer now um I didn't ask for the charge of the chromium but let's take a look at it and see if we can figure it out. So here The bro means each have a charge of -1 together. That would mean that they're -2. But our complex ions charge overall is plus one. This could only happen if the chromium itself was plus three Because we have plus 3 -2 gives me plus one overall. Remember water molecules are neutral so they don't contribute to the charge at all. Alright, so just remember when it comes to a coordination complex, you have to be able to spot the complex ion portion and the counter ion portion, you may also be asked to look at the complex ion and break it down a little bit further into its Liggan portions and its transition metal portion. And when it comes to our Liggins, it's normal to see 2, 4 or six of them connected to our transition metal. Now that we've seen this, click onto the next video, where we dive a little bit deeper into the different types of molecular geometries that are possible based on the number of legends attached to my transition metal.
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now we can say that coordination complexes form predictable geometries based on their coordination and sometimes their electron configuration. So remember the most common types of coordination numbers are 24 and six where we have 24 or six legans attaching to our transition metal. Now, when it comes to our coordination of two, we have two ligand attached to our transition metal. In this case we don't have to worry about the electron configuration of our transition metal so we'll ignore this portion. If our transition metal is connected to just two Liggins, then it's geometry would just be linear. A good example of this is we could have Copper connected to two Bro means and we can say the overall charge is -1. If we were to draw this out it would just be calm per connected to the two bro means and brackets with the charge on the outside. When it comes to a coordination of 4.2 different geometries are possible but we're gonna come back to that. Let's go on to a coordination of six. So if we have a coordination of six because there's only one type of geometry associated with it, we don't have to worry about the electronic configuration of the transition metal. So we'll skip that portion. If your transition metals connected to six Liggins, then we're gonna say that it's geometry would be opta. He'd roll. Now A good example of this. We could use cobalt connected to six ammonia. And let's say that the overall complex ion is plus three in charge. Now, what would that look like? Well, if we're going to take into account three dimensional drawings, we'd have our cobalt in the center, It would be connected to our six ammonia. Okay, so we have one on above and below the plane. Then we'd have to ammonia. Is that are pointing into the paper and then we'd have to ammonia is pointing out of the paper and then we put it in brackets with the overall charge on the outside. Now, going back to our coordination number four, with the coordination number four, there are two possible geometries and and because there's two possible geometries, we can use the electron configuration of the transition metal to determine which one is favored. So with the coordination of four, we're gonna say here that a transition metal with a D 10 electron configuration forms tetrahedron complexes. And if it has a D8 electron configuration, then it forms square planner or planner complexes. So let's go up to our grid. So let's say something with a D 10 electron configuration. A good example is the element of zinc, zinc. Its electron configuration is argon for us to three D 10. So here it's geometry would be tetrahedron. So, if we did an example, we could have ZN and let's say we have O. H. Four and two minus. All right. So if we were to draw this out, we have our Z in in the center we're drawing tetra hydro So for tetra hydro we'd have 10 H. On the plane of the paper. Another O. H. On the plane of the paper, 10. H. pointing down into the paper and then one pointing out from the plane of the paper brackets in the overall charge on the outside. Now this is true whether we're dealing with neutral zinc or zinc plus two ion because remember if we had zinc plus two ions, we'd lose electrons from the outer shell first, which would mean we lose those +24 S electrons. So whether it's in its neutral form or its plus to form, zinc is still classified as having a D. 10 electron configuration. So in both cases it would give us a tetrahedron geometry. Alright, so now four D 8 geometry we could use nickel. Right? So if we have nickel we'd say nickel is argon four S 2 three D 8. And if we're dealing with nickel two plus ion it'd be argon for us to is those two electrons are lost And it will be three D 8. So whether you're dealing with the neutral form or its plus to form it's still AD eight electron configuration. So it would give us a square planner or planner geometry. So example here we could use nickel we could use C. N four two minus. So if we're gonna draw a square planner we'd have a nickel in the center. two of our CNN would point into the plane of the paper and two of them would point out of the plane of the paper brackets overall charge on the outside. So again, it's common for us to see complex ions where we have a coordination number of 246. A coordination of two or six is pretty easy because they only have one geometry connected to them. But when it comes to a coordination of four, then it's important to be able to determine the electron configuration of the transition metal. If we have a D 10 electron configuration for the transition metal, then we're going to form a tetra he'd rel um complex. And if we have a D eight, then we're gonna form a square planner or planner complex. So keep these structures in mind. Keep in mind the electron configuration when it comes to coordination of four and you'll be able to draw any of these complex ions.
Coordination Complexes Exercise 3
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So here in this example, it says determined the geometry for the following complex ion. So here we have chromium as our central element. It's connected to what appears to be for ammonia us And to chlorine. So that's a total of six Liggins. So six Liggins, that would mean our coordination number is six. And that's pretty simple because if our coordination number of six, then there's only one geometry that's possible Octa. He'd roll. All right. So if we're going for symmetry here, we have our two chlorine is drawn on opposite ends, so they're drawn anti to each other. And then we have our four ammonia. As now remember here we have two ammonia as pointing into the plane of the paper and then we have the other two pointing out of the plane of the paper. And because it has a charge, we put brackets with the charge brackets with the charge on the outside. So this would be our structure for this given coordination complex. Now that you've seen this example move down below and take a look at the next one. So in this one, they're asking us to determine the geometry where we have palladium connected to four waters here because there are four waters involved. That means our coordination number is four. So remember, what do you do when your coordination number is for to determine the correct geometry, attempt this one on your own and come back and see does your answer match up with mine. Good luck guys
Determine the geometry for the following complex molecule:Pd(H2O)4.
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