 So, this is the second part of our video on the special case of nitrogen. In the last video, we saw some interesting properties of nitrogen. We also discussed the unique ability of nitrogen to form P pi P pi multiple bonds with itself, which is not present in the higher elements like sulphur, selenium or tellurium. And we also saw that when you compared a single nitrogen bond, that is single Nn bond with the single bonds of the other elements, the single Nn bond is actually weaker because of the small size and higher inter-electronic repulsions. So, let's now talk about how the lack of any MTD orbitals affects the chemistry of nitrogen. Okay? Now, you see, unlike the other members, nitrogen does not have any MTD orbitals because there is no D orbital in the second shell, right? Whereas, if you look at phosphorus, you have the presence of MT3D orbital, arsenic has the presence of MT4D orbital, antimony has MT5D orbitals and so on. So, this means that because nitrogen has only 4 orbitals, that is 1, 2s and 3, 2p orbitals, its covalency is limited to just 4. Whereas, the other members, because they have the presence of MTD orbitals, they can expand their covalency beyond 4. For example, nitrogen can form NF3, but it cannot form NF5. On the other hand, phosphorus can form PF3 as well as PF5. In fact, if you look at PF5, you will see that it has 10 electrons around the central phosphorus atom. Now, remember, covalency is nothing but the number of shared electron pairs formed by the atom of an element, right? Now, nitrogen has 5 valence electrons. It can form 3 covalent bonds by sharing these 3 electrons, right? Like let's say with the hydrogen and it can also donate this lone pair of electrons to form a coordinate covalent bond and this is what you get in ammonium ion. As you can see, in addition to the 3 covalent NH bonds, you also have a coordinate covalent bond. Because of the absence of the D orbitals, nitrogen also cannot form D pi P pi bonds or D pi D pi bonds. This is obvious, right? Because it has no D orbitals at all. On the other hand, the heavier members actually can form these bonds. For example, phosphorus can use its MTD orbitals and overlap with the P orbitals of oxygen or carbon to form R3P double bond O or R3P double bond CH2. As you can see here, the D orbitals of phosphorus overlaps with the P orbitals of oxygen or carbon to form D pi P pi bonding. Just like that, elements like phosphorus and arsenic can also combine with transition metals by forming D pi D pi bonds to form complexes. Because of the absence of D orbitals, such complexes cannot be formed by our tiny little nitrogen.