The density of this material on the atomic scale is then measured by using x-ray diffraction techniques to determine the number of atoms per unit cell in the crystal and the distance between the equivalent points that define the unit cell see Physical Review Letters, , 33, Already a subscriber?
Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Now I can write:. That's not a terrible value for Avogadro's number. Really, it's not. If you take the accepted value of 6.
I call that close enough. The idea works even if my method was a little bit sloppy. Still, my value is better than no value. The biggest problem with the mole is that there is never something that you can see the individual objects as well as a mole of these objects. In a previous post, I estimated what a mole of salt grains would look like. Let me just say that a mole of salt is HUGE.
In fact, if you put this cube of salt in Miami, you could see it from Tampa. Here's what that would look like. Avogadro developed the following idea: Avogadro's Law: If you have two gasses at the same temperature and pressure, they will occupy the same volume only if they contain the same number of molecules. Determining a Value for Avogadro's Number.
Rhett Allain is an associate professor of physics at Southeastern Louisiana University. He enjoys teaching and talking about physics. Sometimes he takes things apart and can't put them back together. Contributor Twitter. If I say I've got a dozen of eggs, how many eggs do I have? Well, if I have a dozen of eggs, that means I have 12 eggs. So, if I say I have a mole of lithium atoms, how many lithium atoms do I have?
That means that I have 6. Exact same idea, it's just that Avogadro's number is much hairier of a number than a dozen. So, let's use our new found powers of the mole and Avogadro's number to start doing some useful things. Let's say that someone were to walk up to you and say, hey, you, I have a How many atoms of germanium am I dealing with? Pause this video and try to think about that.
So, let me clear out some space the periodic table of elements was taking up. All right, so we started off with The first step might be hey, let's convert this to grams of germanium. And so, we can do a little bit of dimensional analysis. We can just multiply this, for every one gram of germanium that is equivalent to 1, milligrams, milligrams of germanium.
And so, if you essentially multiply by one thousandth or divide by 1,, we're gonna get the grams of germanium.
And, you can see that in the dimensional analysis by seeing that that is going to cancel out with that leaving us with just the grams of germanium. And, now that we have an expression for grams of germanium, we can think about moles of germanium. So, how do we do that? Well, we're going to multiply by some quantity, and in the denominator we're going to want grams of germanium for the dimensional analysis to work out, grams of germanium, and in the numerator we want the new expression to be in terms of moles of germanium.
So, one mole of germanium is equal to how many grams of germanium? In this example, this is the same number of significant figures as the A r value.
Calculate the mass of a carbon atom. The Avogadro constant can be used to calculate the mass of a molecule in grams:. Calculate the mass of a bromine molecule. This answer is given to 4 significant figures because both numbers used in the calculation are given to 4 significant figures.
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