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Ch.23 - Transition Metals and Coordination CompoundsWorksheetSee all chapters

# Coordination Complexes

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Sections
Transition Metals
Transition Metals Properties
Coordination Complexes
Naming Coordination Compounds
Coordination Isomers

Concept #1: Coordination Compounds

Transcript

Example #1: Coordination Compounds

Transcript

So here they ask to find the geometry of the following complex ion. So, here we have zinc connected to four ammonia molecules, these are the ligands, and the overall charge is plus 2. Now, remember zinc its electron configuration is argon 4S2 3d10 and remember, we said that if you have a d-10 configuration your shape would be tetrahedral. So, here the shape, geometry would be tetrahedral and if we wanted to draw this out correctly, we have zinc in the center. Remember, tetrahedral means you are connected to four groups. Now, traditionally you probably see it like this NH3 here, NH3 here, NH3 here and here it's the n that's connected and that n is connected to three hydrogen's. So, here I draw it backwards to show the connection is between the zinc, central element, and the nitrogen because it's the nitrogen that has the lone pair being used to make the connection. Now this is not the best way to draw tetrahedral, technically the best way to draw it will be drawing it like this, we still have a zinc in the center, we still have one ammonia molecule up here, but then the remaining three, we draw kind of like that, this would be the more correct way of drawing this connection and here because it has a charge we put it in brackets and they'd be a plus 2 charge on the outside. So, that'd be the correct way of drawing it, we've seen this one, let's see if you can draw the next one, pause the video really quickly, attempt to do it on your own then come back and see if your answer matches up with mine.

Example #2: Coordination Compounds

Transcript

Alright guys, hopefully you pause the video when you attempted to do it on your own, this one is fairly simple, we have gold here but there are only two ligands two bromide ions. So, if your coordination number is 2 then your only shape can be linear, it's when the coordination number is 4 that we have to decide, does it follow a tetrahedral shape or does it follow a square planar or planner shape. So, here we have gold in the center. Remember, linear 180 degree in terms of its bond angle, okay? So, we put this in brackets and the negative charge on the outside, so that would be the way you should have drawn it and remember because there's a charge you put brackets around it ,and the way the formula is presented to us should have brackets in it. Now, now that we've done this one try to attempt to do this practice one on your own, come back and see how best I draw. Now, remember just like tetrahedral there is an ideal way to draw this particular shape, draw it first the way you would like to see it and then we'll see if your shape matches up with my shape. So, good luck guys.

Practice: Determine the geometry for the following complex ion: [Cr(NH3)4Cl2]2+

Concept #2: Ligands

Transcript

Hey guys. in this new video we're going to take a look at ligands. So, we're going to say a ligand can be thought of as just simply a lewis base because remember, a Lewis base is an electron pair donor. So, what happens here is that the transition metal in the middle is a cation. So, it's positive so it can easily accept negative electrons, the metal cation in the center is the Lewis acid, which is an electron pair acceptor, the ligand, which can be either neutral or negative donates its lone pairs to the central metal. Now, I'm going to say ligands can be characterized by the number of elements in the molecule that can donate a lone pair. Now, we're going to say here, that these compounds use their lone pairs to grab on to these metal cations and therefore they're referred to as chelating agents. So, chelating agents. Now, chelating agents, we're going to say that Chela is Greek and it means crabs claw and basically what happens here is that the lone pair kind of act like teeth that kind of chump into the metal cations, when it's donating its lone pairs actually surrounding and holding on to that metal cation performing a strong bond. So, that's where the term chelating agent comes from. Now, we're going to say ligands that possess only one element, able to donate a lone pair, referred to as monodentate ligands, when we say monodentate, monodentate means 1-2, because again, we think of them as claws or teeth that connect to the metal ion, common ones here we have water of course only one lone pair is being donated to form the bond not both, here X, X just stands for halogen. So, we're talking about chlorine, chlorine, bromine and iodine, technically since they're negative we're talking about fluoride chloride, bromide and iodide. Now, when you get to organic for those of you are brave enough to go into organic you'll learn that X is just the default symbol to represent all halogens. So, take note of that, when you see x in chemistry religious refers to some type of halogen, next we have our cyanide ion. Now, nitrogen also has a lone pair but it's the carbon that possesses the negative charge, it's the carbon that's going to be attacking with its lone pair, here we have our hydroxide ion, we have ammonia.