Molecular weight

• The molecular weight is the weight of the combination of all the atoms inside a molecule

• Let's take H20 , now to calculate the molecular weight of h20 we have to add the weight of 2 hydrogen and oxygen , 1.00784 + 1.00784 + 15.999 , the molecular weight of h20 would be 17.915 , this is how we calculate the molecular weight of a molecule

Avogadro's number and mole

• We introduced ourselves to the idea of average atomic mass, which we began to realize could be a very useful way of thinking about a mass at an atomic level, or at a molecular level. You're very unlikely to just be dealing with one atom, or just a few atoms, or just a few molecules. You're more likely to deal with several gram of an actual substance.

• They said, all right, let's think about a given element. So, say, lithium. We know its average atomic mass is 6.94,6.94 unified atomic mass units per atom, atom of lithium. What if there were a certain number of atoms of lithium such that if I have that number, so time, certain, certain number of atoms, then I will actually end up with 6.94 grams, grams of lithium. And, this number of atoms is 6.022140 times 10 to the 23rd power.

• You will have a mass of that same number in terms of grams. Now, you might be saying, is there a name for this number, and there is indeed a name, and it is called Avogadro's number

• Mole means that you have 6.022140 times 10 to the 23rd power of something , for example 6.022140 times 10 to the 23rd power of carbon is a mole