Molecules are the building blocks of matter.

You've probably heard that before, right? But that does it mean? What does a molecule look like? How big are they?

While you technically can measure the size of a molecule, despite the fact it's usually too small to do even with a regular microscope, what you can't do is see an image of the molecule itself. The reason has to do with the limits of nature and wavelengths of light, not because our technology isn't there yet, or we're not smart enough to figure it out. Scientists have to get creative about the ways they do about measuring something that isn't possible to see with the eyes.

Here's a cool experiment you can do that will approximate the size of a molecule. Here's what you need:

[am4show have='p8;p9;p28;p55;p68;p101;p52;p91;' guest_error='Guest error message' user_error='User error message' ]

Materials:

  • liquid dish soap
  • chalk dust
  • medicine dropper
  • pie pan
  • ruler
  • water
  • calculator

Download student worksheet and exercises here!

  1. Place water in the pie pan and sprinkle in the chalk dust. You want a light, even coating on the surface.
  2. Place dish soap inside the medicine dropper and hold it up.
  3. Squeeze the medicine dropper carefully and slowly so that a single drop forms at the tip. Don't let it fall!
  4. Hold the ruler up and measure the drop. Record this in your data sheet.
  5. Hold the tip of the dropper over the pie pan near the surface and let it drop onto the water near the center of the pie pan.
  6. Watch it carefully as it spreads out to be one molecule thick!
  7. Quickly measure and record the diameter of the layer of the detergent on your data sheet.
  8. Use equations for sphere and cylinder volume to determine the height (which we assume to be one molecule thick) of the soap when it's spread out. That's the approximate width of the molecule!

[/am4show]

Click here to go to next lesson on Mole Concept.

 


Have a question ?

Tell us what you're thinking...

Comments

10 Responses to “Measuring a Molecule”

  1. Oops! Yes I forgot the 2 in the equation, so sorry about that!

  2. amyelizabeth_imbody says:

    Hi! At around 11:36 in the video when D is being computed, are we to use r-squared in the denominator of the equation? If so, wouldn’t that be (2.625)squared? I may be missing something, though.

  3. Aurora Lipper says:

    I checked the video and it is coming up for me. Please be sure that you are logged in. If you still can’t see the video, please try a different web browser.

  4. carolinametzgers says:

    There is no video.

  5. Oh no! I just replaced this worksheet last week because it had errors, and now I see it went back to the original one! I’ll repost it now so you can re-download it. Thanks!

  6. kjoykonnection says:

    How do I figure out the length of the oil molecules in the worksheet without the radius of the spill?

  7. Oh no! Yes, please do send an email along so I can help!

  8. Also having trouble with end of lab problems. Sent you an email with work my daughter did to attempt to solve it.

  10. Lisa Pearson says:

    We are having trouble with the problems at the end of this lab. Could you explain how you got your answer? I’ve used the formulas given in the lab and am not coming up with anything close.