 In this video, we will explore the magnetic properties of transition metals. You see, an electron is a negatively charged species, right? It spins on its own axis and also goes around the nucleus. Now this orbital motion and the spin create a tiny magnetic field around the electron. And this is why an unpaired electron can be thought of as a tiny magnet with distinct magnetic movement. And when this electron with its unique magnetic movement is placed in an external magnetic field, it interacts with it. Now a material which has unpaired electrons would have random alignment when there is no magnetic field. But in the presence of an external magnetic field or an applied magnetic field, these electrons would get aligned and as a result, as you can see here, such materials will get attracted to the magnetic field and the field lines will bend towards it. On the other hand, materials with paired electrons tend to oppose the external magnetic field and as a result, such materials get repelled by the magnetic field. And here, these external magnetic field lines would move away from this material. So in the first case, where the material gets attracted to the magnetic field or the ones with unpaired electrons are called paramagnetic materials. And those materials that get repelled by the magnetic field or the ones that have paired electrons are called diamagnetic materials. In addition to these two, we have one more type of materials called the ferromagnetic materials. Now these are the materials that are very strongly attracted to the magnetic field. Ion, cobalt and nickel are ferromagnetic in nature. In fact, we can say that ferromagnetism is an extreme form of paramagnetism and the compounds of these elements exhibit magnetic properties even in the absence of magnetic field. So this is why these materials can form permanent magnets. Now as transition metals have plenty of unpaired electrons, in this video we are going to be talking mainly about paramagnetism exhibited by transition metals. Now as I said before, paramagnetism arises due to the presence of unpaired electrons and every electron has an intrinsic magnetic dipole moment associated with it. Now the spin of a single electron denoted by the quantum number MS can be plus half or minus half. Now when the electrons get paired, the spin also gets negated, right? That means the magnetic field produced in the case of a paired electron is much less than the magnetic field produced by an unpaired electron. And more the number of unpaired electrons, greater would be the paramagnetic effect. For the compounds of the 3D series transition metals, the magnetic moment is governed by the spin-only formula which is mu is equal to under root of N into N plus 2, where N is nothing but the number of unpaired electrons and mu is in the units of Bohr magneton. Now the interesting thing is if you have the value of the magnetic moment, you can kind of figure out how many electrons or how many unpaired electrons are present in that particular metal ion. For example, if the observed magnetic moment of a particular ion in a solution is zero, what information does it give us about the number of unpaired electrons in this particular metal ion? Now zero magnetic moment would mean that there are zero unpaired electrons, that is N is equal to zero. And that's exactly what happens in Scandium 3 plus ions. The observed magnetic moment for Scandium 3 plus is zero. And that's not surprising at all because in Scandium 3 plus ions, the three electrons that are present in the 4S and 3D orbitals are gone. That is it essentially has a noble gas configuration. Just like that, zinc in divalent state also has magnetic moment which is equal to zero. Because here again, zinc does not have any unpaired electrons and from its configuration, we can see that it has completely filled 3D orbitals. Okay, so let's now do a simple calculation. Try figuring out the magnetic moment for MN 2 plus ions. So pause the video and give it a try. So it's quite simple, isn't it? All you need to do is first figure out the number of unpaired electrons that are present in MN 2 plus ions and then simply substitute that value in this particular formula. So the electronic configuration of MN 2 plus is nothing but argon 3D5. That is it has five unpaired electrons. So here N would be 5. By substituting the value in this formula, you will get mu is equal to under root of 5 into 5 plus 2. And on calculating, we get the value which is 5.92 and this is quite close to the observed value which is 5.96. Similarly, you can calculate the magnetic moment for the other transition metal ions using this particular formula. So if you look at the trend of the magnetic moment for some of the ions of the 3D series, we can see that the value increases as we go towards the middle of the series, that is towards manganese because here the number of unpaired electrons is increasing and then the values start decreasing as the number of unpaired electrons decrease. So what you see here are the calculated values of magnetic moment. But if you compare them with the experimental values or the observed values, you can see that they are very close to their actual values. We will explore more about the magnetic properties of transition metal ions in the next unit of coordination chemistry.