04/02/2024
Continuing my “one billion is a big number” series… I got to wondering how big a billion oxygen atoms would be. The thought of a really large number of a really small thing intrigued me.
This took some refreshing of my physics education (and I’ll say up front i did not fact check all this, but did check two or three sources).
The Periodic Chart tells us atomic mass, which is mostly a count of its protons and neutrons. But i wanted a width, or more appropriately, a diameter. The diameter of an atomic sphere is tricky due to the electron orbits. So instead they measure how closely atoms can be placed together, then calculate a radius. And the unit of measurement is a “pm” picometer, or one trillionth of a meter. A billionth of a meter is a nanometer (also 1,000 pm).
Most of the elements range from a radius of about 140pm to 250pm, with a few outliers below like Hydrogen at 120, and one really above like francium around 350. And the sizes are not intuitive, e.g. heavier atomic mass elements like lead and gold are not necessarily proportionally bigger than elements like oxygen and helium.
Back to my topic… how long would one billion oxygen atoms be laid side-by-side? The radius is 150pm, or 0.150 nm. A billion nm is one meter, so 0.150 nm * 1 billion = 0.150 meter, or 150 mm! Divide by 25.4 and that gives you 5.9 inches. So, where a billion seconds is 31.7 years, a billion oxygen atoms in a line is 5.9 inches. WOW!