Anyway, I just had one of those moments. I was reading a post in a blog on statistical modeling, and I followed the link to the paper cited. And in reading the abstract, I suddenly realized why it’s called the periodic table.

Of course I know what periodic means, and I learned a bit about the periodic table in my two chemistry classes. But I guess I never asked myself why it’s called the periodic table. Now I realize it’s because, for at least a certain portion of the table, elements 18 “units” apart from another share certain properties. So there’s a periodicity of 18 for part of the table. Whoa!

I suppose part of the reason is that when I learned about properties of the elements in the periodic table, I was probably about twelve, and the word periodic didn’t mean much to me. But I took one other course in chemistry as an undergrad, and I must have understood what periodic meant by then….

Does everyone know this and I just somehow missed it?