 In this video, let's understand how to calculate the molecular weight of a molecule. So, first off, what is molecular weight? Well, we can say that molecular weight is the sum of atomic masses of all the atoms in the molecule. For example, let's say we take calcium chloride. Now, calcium chloride has two types of atoms. It has one of calcium and two atoms of chlorine. So, molecular weight would be the sum of the atomic mass of calcium and two atoms of chlorine. Now, what is the atomic mass of calcium? Well, for that, we can have a look at the periodic table. So, when we look at the periodic table and try to find calcium, this is where it is. This right here is calcium. And if you look closely, the atomic mass is 40.08. So, atomic mass is usually written below the symbol of the element, right? So, this is 40.08 plus 2, because there are two chlorine atoms, 2 into the atomic mass of one chlorine atom. Chlorine is over here and the atomic mass is 35.45. So, this is 35.45. Now, we can calculate this and find the molecular weight of calcium chloride. When we do this, this comes out to be equal to 110.98. And this will be atomic mass unit, which is represented by small u, because all of these numbers that you see below the symbol of the element, they are in atomic mass units, that is small u. One atomic mass unit is equal to... This is equal to 1.67 into 10 to the power minus 24 grams. I think it's 24. Yeah, this is minus 24 grams. All right, now let's have a look at some more molecules. So, now we have C2H4. This is ethene. Now, this one has two types of atoms, carbon and hydrogen, but it has two carbon atoms and four hydrogen atoms. And molecular weight is the sum of the atomic masses of all the atoms in that molecule. So, this would be 2 into the atomic mass of the atomic mass of carbon, plus 4 into the atomic mass of hydrogen. So, atomic mass of carbon, if you look at a pitotic table, this is carbon aside over here, this is 12.01. So, 2 into 12.01 plus 4 into the atomic mass of hydrogen, which is over here. And this is 1.008. Now, when we solve this, this comes out to be equal to 28.052. Again, atomic mass units. Now, let's take one which is slightly more complicated. Let's take one with three types of atoms. How about C6H12O6? All right, now this is really glucose. It has six carbon atoms, 12 hydrogen and six oxygen. Why don't you try and calculate the molecular weight of glucose? Okay, hopefully you gave this a shot. Now, this will be 6 into the atomic mass of carbon, 12.01, plus 12 into the atomic mass of hydrogen, 1.008, plus 6 into the atomic mass of oxygen. And oxygen is over here, this is oxygen. So, the atomic mass is 16.00, let's just write 16. Now, when we solve this, this comes out to be equal to 180.156 atomic mass units.