in this video we're going to talk about complex ions but first what is a complex ion a complex ion is the combination of a transition metal cation with a ligand molecule or ligand ion so let's use an example here we have the silver metal cation it has a charge of plus one and we're going to react it with two ligand molecules in this case two ammonia molecules in this case the ligand is not an ion it's a neutral molecule and it's going to form this particular complex ion the diamine silver cation now what is the
coordination number of that complex ion the coordination number is two because it's attached to two ligand molecules so this is the ion or the metal ion this is the ligand and here we have the complex ion now for complex ions that have a coordination number of two the geometry will be linear as you can see from this particular drawn and so that's a basic introduction into complex ions so now let's look at another example the hexa cyano ferry ion identify the ligand and also determine the coordination number and the oxidation state of fe the ligand
in this example it's not a molecule but it's a polyatomic ion in this case it's cyanide which has a lewis structure that looks like this the carbon bears the negative charge or the negative formal charge now the coordination number is basically the number of ligand ions attached to the transition metal cation so the coordination number in this example is six now how can we determine the oxidation state of fe would you say it's positive 3 negative 3 positive 4 negative 2 what is it well let's write a reaction so we know that fv probably has
some charge which we'll call x and it's going to react with six cyanide ions to produce the hexa cyano ferrate ion almost lost the word there so let's write an equation where the total charge will remain balanced so fe has a charge of x cyanide has a charge of negative one but there's six of them and the product ion or the complex ion has a net charge of negative three so x minus six is equal to negative three so if we add six to both sides we can see that x is negative three plus six
or plus three so this is the oxidation state of fv so fe has a positive three charge now there was a guy called alfred werner and he came up with a theory for coordination compounds and transition metal ions and it basically stated that transition metal ions have two types of valence and that is that the way that these metal cations can combine with other things like ligands and ions and the two types of valence that these metal ions can have is called the first one is the primary valence and the second one is the secondary
valence perhaps you've heard of these terms and in the case of the fe3 plus ion as it relates to this particular complex ion what do you think the primary valence and the secondary valence of this transition metal cation is the primary valence has to do with its oxidation state and that's the way it forms ionic bonds the secondary valence has to do with the coordination number and so it relates to how it interacts with uh ligands and those ligands could be ions or molecules so in this case the primary valence is positive 3 because that's
the oxidation state of fe and the secondary valence is 6 because the coordination number is six it could be attached to six ligands now what type of geometry does the fe cn6 dre minus ion have if the coordination number is six the geometry will be octahedral and so it's going to look like this and so that's how you can draw this particular complex ion and if you want to show the octahedral structure you could you can make it look like this so that's the octahedral structure of this particular complex ion now if the coordination number
is four then there's two types of geometries that can occur one example is the tetrahedral geometry another one is the square planar geometry so the tetrahedral geometry looks something like this or it can have a square plane of geometry which looks like this so if you have a coordination number four the geometry could be any one of those two so keep that in mind now let's talk about the coordination numbers for certain transition metal ions now let's say if we have a transition metal ion with a charge of plus one such as copper plus or
a g plus the coordination number of copper plus one is two and four for silver it's only two and so if the charge is low the coordination number is relatively low but notice what happens if we increase the charge let's say to plus two so cobalt for example the cobalt two plus on can have a coordination number of four or six nickel two plus is the same fe2 plus can be up to six and zinc two plus can be four or six now let's look at the plus three ion one example is gold three plus
which has a coordination number of four chromium three plus has a coordination number six and cobalt three plus has a coordination number of six so notice the general trend as the charge on the transition metal ion increases the coordination number generally increases and it makes sense because if a metal ion has a very high charge it makes sense that it can bind to more ligands now you need to be familiar with the different types of ligands the first type is called a unidentate also known as a mono dentate ligand so uni and mono is associated
with the number one so this tells us that the ligand can only make one interaction with a metal ion some good examples of these types of ligands are water ammonia chloride cyanide thiocyanate just to name a few so in the case of ammonia it has one lone pair and so it can only form one interaction per molecule with a transition metal ion a bidentate ligand can have two interactions per molecule bi is associated with the number two so one example is the oxalate ion it has two oxygen atoms with a negative charge and let's use
a zinc metal cation so this is one interaction and that's another so there's two interactions per molecule which makes it a bidentate ligand another example is ethylene diamine which you can abbreviate it as en so this particular ligand can also make two interactions each nitrogen atom has one lone pair which can bind with a transition metal cation so this is one interaction and this is the second interaction so that makes ethylene diamine a bidentate ligand so those are known as chelating lincolns a chelated ligand can interact with a metal ion in more than one way
so biodentate ligands are chelated ligands now let's talk about coordination compounds and here is an example a coordination compound is neutral overall but it consists of a complex ion and a counter ion what do you think is the complex ion in this example well you can clearly see it it's in brackets in this particular example and so it's cr and h36 now what do you think the charge or the oxidation state of chromium is in this example now we know that cyanide has to be the counter ion it's there to balance the charge on chromium
and there's three of them which indicates that chromium has to have a plus three charge so this particular complex ion has a positive three charge so this is the complex ion and in this example this is known as the counter ion the counter ion that we have in this example is negatively charged so it's called an anion but it doesn't always have to be an anion it can be a cation in this example the complex ion is the cation and so the counter ion has to be an anion but sometimes the roles can be reversed
like in this example k3 fe cn6 so this is the cation and this has to be the anion so this time the anion is the complex ion fe cn6 with a negative three charge and the cation is the counter ion which is used to neutralize the negative three charge of the complex ion and so we have three of them and so the coordination compound is always neutral then that charge has to be zero so that's it for this video hopefully it gave you a basic introduction into complex ions ligands and coordination compounds thanks for watching
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