The molecule is the smallest particle of substance which is the carrier of its chemical properties. The molecule electrically is neutral. Chemical properties are defined by set and a configuration of chemical bonds between the atoms which are its part. Its sizes, in most cases, are so small that even in a tiny sample of substance their quantity is unimaginably huge.
Instruction
1. Present that you have some capacity which is densely filled with small identical balls. You know, for example, that the lump of these balls – 1 ton, and their quantity – 10 thousand pieces. How to find the mass of one ball? As easy as shelling pears: having divided 1000 kg into 10000 pieces, receive: 0.1 kg or 100 grams.
2. The role of quantity of balls will play so-called "mol" in your case. This amount of substance in which contains 6.022*10^23 its elementary particles - molecules, atoms, ions. In a different way this size is called "Avogadro's number", in honor of the famous Italian scientist. Value asking any substance (molar weight) in number coincides with its molecular weight though it is measured in other sizes. That is, having summarized atomic the weight of all elements which are a part of a molecule of any substance (taking into account indexes, certainly), you define not only the molecular mass, but also numerical size of its molar weight. Here it also plays a role of mass of those balls in the previous example.
3. Review a concrete example. Widely known substance – extinguished lime, hydroxide of Sa calcium (ON) 2. The atomic weight of its elements (rounded, expressed in atomic units of mass) is 40 for calcium, 16 for oxygen, 1 for hydrogen. Taking into account index 2 at a hydroxyl group, receive molecular weight: 40 + 32 + 2 = 74. Therefore, 1 mol of hydroxide of calcium will weigh 74 grams.
4. Well, and further the problem is solved elementary. Contains in 74 grams of this substance 6.022*10^23 molecules. How many does one molecule weigh? Having divided molar weight into Avogadro's number, you receive: 12.29*10^-23 gram. (Or 12.29*10^-26 kg). Such is the answer. Certainly, the problem of finding of mass of a molecule of any other substance is the same way solved.