What Are Atoms Made Of?

This post starts with the the slides of an elementary talk I gave at Sloans Bar and Grill, in Glasgow, as part of a wonderful series called A Pint of Science. At the end I include some fascinating details which I only had time to briefly touch on in my talk. Start with a hair: A red blood cell is ten times smaller across: A flu virus is 10 times smaller across than that: The flagellum of this cell is ten times smaller across than that: A molecule of hemoglobin is about ten times smaller than that: A water molecule is ten times smaller than that: A hydrogen atom is 5 times smaller than that: This is an actual image of a single hydrogen atom, which is amazing. (Read more here.) But how did people figure out that atoms even exist, back before we could see individual atoms? And how did we figure out what they’re made of? It started with chemistry. Two liters of hydrogen burn with one of oxygen to form one liter of water vapor, so we guess water is made of 2 atoms of hydrogen and 1 of…