Periodic table of elements (as of 2016)
Image credit: Dmarcus100 [<a href="https://creativecommons.org/licenses/by-sa/4.0">CC BY-SA 4.0</a>], <a href="https://commons.wikimedia.org/wiki/File:Periodic_Table_Of_Elements.svg">from Wikimedia Commons</a>

The periodic table of elements has undergone numerous expansions and revisions over the years. Today, we celebrate the day in 1863 when J.A.R. Newlands published an early version of the table, featuring 56 elements in 11 groups based on what he called the “Law of Octaves.” We’re now up to 118 elements, and although there are various versions of the table in circulation, they’re all ways to group elements by shared characteristics, and they make the study of chemistry a great deal easier than a simple list would. I’ll award 5 bonus points to the first person who memorizes the entire table today and can reproduce it from memory.