• Question: how many atoms are in a hand?

    Asked by lolly to Ajay, Kate, Kuntal, Pip, Reka on 8 Nov 2016.
    • Photo: Kate Elliott

      Kate Elliott answered on 8 Nov 2016:

      Good question, this has taken a bit of investigation!
      Google says there are approximately 7×10^27 atoms in a 70kg person. My office friends have estimated that a hand weighs around 300g. This would mean in a hand there were 3×10^25 atoms which can be written more normally (but longer) as:

      30 000 000 000 000 000 000 000 000 atoms

      But that’s a guess! I can definitely confirm that it is a lot though!

    • Photo: Reka Nagy

      Reka Nagy answered on 8 Nov 2016:

      Let’s see – it is estimated that an adult human has about 7 billion billion billion atoms (that’s a 7 followed by 27 zeros!!).

      Your hands take up about one half of a percent of your total body weight – so one hand takes up about a quarter of a percent, or 0.025th of your total body weight.
      So we multiply 7 billion billion billion by 0.025 and get what is still a very large number – 175 followed by 24 zeros!

    • Photo: Pip Millington

      Pip Millington answered on 9 Nov 2016:

      Lolly, I don’t think I can do much better than Kate and Reka at answering how many atoms are in a hand itself but a related interesting question is how many atoms you can hold in your hand?

      I’m going to guess most school-age people would be able to hold something about 5kg heavy in one hand, at least for a short time. Intuitively you might think that something solid like a iron weight would be a good place to start but in fact iron is on the fourth row of the periodic table so atoms of iron are heavier than those on the top 3 rows. This means you get fewer atoms for the same weight!

      I hadn’t thought about this before but working out which substance gives you the most atoms per kilogram is a little tricky. We might go to the lightest atom hydrogen but that’s a gas H2 in its elemental form. The best strategy is to find a structure that has lots of hydrogen in it and is a solid at room temperature. The best solution to this I can think of right now is paraffin/vaseline because its a mixture of compounds containing just carbon (element 6) and hydrogen (element 1) with an average chemical formula of something like C25H52.

      If you managed to obtain 5kg of it of paraffin and held it in your hand you’d be holding roughly 6.5 x 10^25 or
      65,000,000,000,000,000,000,000,000 atoms in your hand.

      Phew!

Comments