Science's basic book of ingredients just got a little bigger

It says something about Dmitri Mendeleev that he had an easier time keeping track of the number of protons in the nucleus of an atom than the number of brothers and sisters living under his roof. The nineteenth-century Russian chemist was the youngest of 11 siblings—unless it was 13 or 14 or maybe 16. No one ever knew, and he never clarified things for his many biographers. But then he had much bigger—and, on an elemental scale, much smaller—things on his mind.