Avocado’s Number

No, no, get a grip, Isabel. It’s Avogadro’s number, and I haven’t thought much about it since I first encountered it in high-school Chemistry class, lo, these 50 years ago now. Nor did I know much about it even back in the day.

I never knew, for example, that Avogadro was an Italian lawyer’s last name, or if I did know, it did not stick.

Likewise, I never knew that the number was not determined by Amadeo Avogadro (which sounds much cooler in Italian than in English). No, after Avogadro’s other number came up in 1856, Avogadro’s number as we know it (or as we don’t) was determined by some other guys:

  • Josef Loschmidt, an Austrian high-school teacher who is credited as being the first person to estimate the number of particles in a given quantity of matter, in 1865 (presumably the first to estimate this number with precision more exacting than “a whole bunch”)
  • Jean Baptiste Perrin, a French physicist who coined the term and reported an estimate of it in 1909 based on his work on Brownian motion, the discovery of which in 1827 by Robert Brown, a Scottish botanist, had demonstrated the active nature of molecules

It’s sort of cool, I think, that this story includes so many nationalities — Italian, Austrian, French, Scottish — and so many unchemical occupations — lawyer, teacher, physicist, botanist. It’s at once largely incomprehensible and amazingly inclusive. And it’s cool that even 50 years after your death someone might name something both fundamental and lasting after you (but not, apparently, 50 years after your high-school graduation).

But what is that something, you ask? For any others who’ve forgotten or never knew their high-school chemistry, here’s Wiki’s take on it:

The Avogadro constant (NA or L) is the proportionality factor that relates the number of constituent particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample. Its SI unit is the reciprocal mole, and it is defined as NA = 6.02214076í—1023 mol−1. . . The numeric value of the Avogadro constant expressed in reciprocal mole, a dimensionless number, is called the Avogadro number, sometimes denoted N or N0, which is thus the number of particles that are contained in one mole, exactly 6.02214076í—1023.

All right then. Not having day-to-day familiarity with proportionality factors or dimensionless numbers, and although I would not heretofore have said that they are a model of accessibility, I even prefer how Scientific American explains it . . .

. . . the number of particles in a unit known as a mole . . .

although I never actually got that whole(y)/holy mole(y) thing, either.

Really, I prefer-er how William McGuire Bryson explains it . . .

 . . . the number of molecules found
in 2.016 grams of hydrogen gas
or an equal volume of any other gas . . .

although I get confused when we jump from units of weight to talk of volume.

Bryson gives the actual Avogadro number (6.0221367 x 1023) (and no, Bryson’s number and Wiki’s do not match and I have no idea why not), and then he notes that it’s a Big Number. But — and here, finally, is the payoff — if you, like me, have little intuitive feel for just How Big once you get past, oh, 103, Bryson has help.

Chemistry students have long amused themselves
by computing just how large a number it is,
so I can report that it is equivalent
to the number of popcorn kernels
[Ed.’s question: Popped or unpopped kernels?]
needed to cover the United States to a depth of nine miles
[Ed.’s admission: OK, at 9 miles it likely doesn’t matter.],
or cupfuls of water in the Pacific ocean,
or soft drink cans that would, evenly stacked,
cover the Earth to a depth of 200 miles.
An equivalent number of American pennies
would be enough to make every person on Earth
a dollar trillionaire.
[Ed’s question: Are there persons elsewhere?]
It is a big number.
A Short History of Nearly Everything

Indeed it is. I don’t know about you, but I was not amusing myself in Chemistry class by doing any of these calculations, although amusement I surely and sorely needed. Where was Bill Bryson then? I don’t know, but I’m glad he’s here now.

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18 Responses to Avocado’s Number

  1. Tom Watson says:

    Well, you’ve certainly cleared that up for me. And hat’s off to Bill Bryson!

    I’m wondering…what if I had to know this in order to vote?

  2. Marilyn Smith says:

    You lost me at ‘number’, Isabel.

  3. Huh? I am certain this is important. And I am glad someone else is responsible. Thanks for a glimpse into the depths of what I will never know!

  4. “Bill Bryson then” was growing up in Iowa with my husband and his brother, who sometimes babysat for wee Billy. Their parents (all four of them) were journalists with the Desmoines Register.

    • barbara carlson says:

      My goodness, so few degrees of separation!

      I am a big fan of his writing — Lost Continent, Thunderbolt Kid, Notes from a Small Island (read 3X), etc. They are worth re-reading. So rich.

  5. Jim Taylor says:

    A while ago, I decided to see if I could get an avocado seed to sprout. All it requires is a seed, a glass of water, and three toothpicks. Wonder of wonders, it worked. After about two weeks, a sprout came up. Naturally, I called it Ava. (I’d send a photo, but I don’t think they’ll attach.) Then a second sprout came up, and since they were twins, of course I called it avA. I’m thinking now I should have called it Gadro.
    Jim T

    • Isabel Gibson says:

      Jim – 🙂 It’s not too late. Your nearest provincial-services office can give you the form you need for changing a name given at birth.

  6. barbara carlson says:

    I am not proud of this confession, but the only math that I ever use from school is how to determine a percentage. As in by what percentage are we down in sales this year over last year. And I still have to remember which number I need to subtract from which year and THEN divide by the first number. I CAN do this. But really for the rest of the above…I am ashamed.
    I actually loved Algebra and sailed through it, then I hit calculus, the brick wall. Then the algebra sailed right through me and out again.
    Sometimes I wonder if I ever really WENT to school…

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