Sigma and Pi Bonds Explained, Basic Introduction, Chemistry PROFESSOR: In this video, I'm going to give you a brief introduction into sigma and pi bonds. So what you need to know is that a single bond is a sigma bond. A double bond contains one sigma and one pi bond. A triple bond contains one sigma and two pi bonds. So I'm going to use ethene as an example. The Lewis structure of ethene looks like this. So every single bond that we see here is a sigma bond, and sigma bonds are formed from the overlap of atomic orbitals. The carbon is SP2 hybridized, and hydrogen has an S hybridization. So therefore, once we mix the S orbital with the SP2 orbital, that produces a sigma bond. So this is another sigma bond. So this one is formed from the overlap of two SP2 hybrid orbitals. So as you can see, this molecule has five sigma bonds-- 1, 2, 3, 4, 5. Now the pi bond arises due to the unhybridized P orbitals that exist above and below the single bond. So this forms the pi bond. And the sigma bond is in the middle. So now you can visually see how the sigma bond and the pi bond, how they look alike and how they differ. So all of these are sigma bonds. So in this molecule, we have five sigma bonds and one pi bond. So let's work on some problems. So I'm going to give you a molecule-- C2H2, also known as acetylene. And what I want you to do is I want you to draw the Lewis structure and determine the number of sigma and pi bonds that can be found in this molecule. So feel free to pause the video and give this problem a shot. Go ahead try it. Acetylene can be drawn this way. It's important to know that hydrogen likes to form one bond, and carbon likes to form four bonds. So first, you want to draw the molecule with symmetry. Now in order for carbon to have four bonds, we need to put a triple bond in the middle. This is the Lewis structure of acetylene. It's a linear molecule. Now how many sigma and pi bonds are present in this molecule? Now keep in mind, every bond contains one sigma bond. So it's 1, 2, 3. There are three single bonds in this molecule. Now a triple bond has two pi bonds. So we have three sigma and two pi bonds. That's all you got to do. Here's another example that you could try. Draw the Lewis structure of this molecule and determine the number of sigma and pi bonds that are present in it. So carbon has to be the center atom because it can form the most number of bonds-- four bonds. Hydrogen can only form a single bond, and oxygen likes to form two bonds. So with that knowledge, we know that this has to be the structure. So we could see that we have 1, 2, 3 sigma bonds, and we have a double bond which contains one pi bond. So that's the number of sigma and pi bonds found in Ch2O, also known as formaldehyde. Now let's try another example-- SO2Cl2. How can we draw the Lewis structure of this molecule? Sulfur can form up to 6 points. It has six valence electrons, and if it gives away all six, it could form six bonds to do so. Oxygen likes to form two bonds, and chlorine likes to form one bond. So having that knowledge, we could assemble the structure like this. So that's SO2Cl2. Now how many sigma bonds and pi bonds do you see in this molecule? So every bond has at least one sigma bond-- so 1, 2, 3, 4. There's four sigma bonds. And each one contains one pi bond. So we have a total of two pi bonds. And it's basically counting. That's all you need to do in order to determine the number of sigma and pi bonds. So I'm going to give you a more complicated structure. Determine the number of sigma and pi bonds in this compound. So all you got to do is just count the number of bonds to get the sigma bonds-- 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. So there are 11 sigma bonds. The triple bond has two pi bonds, the double bond has one. So we have a total of three pi bonds.