Communicating Data with Periodic Tables
/I think periodic tables might just be the most ubiquitous infographic. I have zero data to back up this assertion. It’s just something that chemists use all the time, and most chemists I know tend to have one handy at a moment’s notice, or decorate their offices with them. They never seem to have just one. Even chemistry classrooms tend to have more than one, so I think it’s worth considering the periodic table’s ability to communicate information. Some periodic tables are pretty sparse. Some are hugely information dense (here’s a favorite of mine). And, as a recent article in C&EN points out, although there’s a common shape, there isn’t even a consensus on the “one true way” to arrange a periodic table.
Last May I found this periodic table while browsing through old books in my university’s library.
Periodic Chart of the Elements from inside cover of Gaines, Binder & Woodriff, 1951.
It’s from a 1951 textbook (Gaines, Binder & Woodriff), so it’s not terribly surprising that there are fewer elements (96 instead of 118) and some of the symbols have changed (e.g. A for argon, Fa for francium, Cb for columbium, which was later renamed niobium). What made it jump out to me at the time is the arrangement of the table itself: what I’m used to seeing in the middle of the table as the d-block is wrapped around in doubled rows. Copper, silver, and gold are in the same column as lithium, sodium, and potassium! 15 rare earths (La-Lu) are noted in a single cell, but not identified individually, and elements 89-96 are incorporated into the table, rather than segregated on an island of misfit actinides.
I’m told this arrangement was common in the Soviet Union. That it appears in an English-language textbook in 1951 seems interesting, and I wonder if it became less common in the US as the Cold War carried on.
What has struck me since that first look are the choices the creator of this table made about which information to include about each element, and how it’s presented.[1] We have atomic numbers, symbols, atomic weights, and the number of electrons in each shell. But, wait, there’s more: small text at the top of the table explains the horizontal lines running through the table cells:
- “% area below dotted lines indicates relative ability to lose electrons”
- “% area above broken lines indicates relative ability to gain electrons”
First, I’m curious now what method or measurement they used to rate ability to gain/lose electrons. Since they are relative quantities, I wonder what they are relative to? (I suppose it’s time to go back to the library and take another look at that old textbook.)
Second, I think the use of the different line styles to convey relative values is a neat trick. They are subtle, yet distinct, and they’re even read from opposite ends of the table cell (area above vs area below). Look along the fourth row (K→Ni) and watch the dotted line drop. You can see the periodic trend in ability to lose electrons! And using the same table you can see the trend in ability to gain electrons!
Several textbooks I’ve used have included figures with the periodic trends as 3D column charts. I don’t love them. 3D charts are really difficult to read because the depth or apparent volume tends to distort the actual differences in size. As a physical object I’d bet they’re useful (like these 3D-printable models), but as an image on a page or screen, I’m not enthused. The periodic table shown above, though, shows two of those trends clearly in a single figure. (Even those 3D printed models show only one trend at a time.) That’s pretty cool.
[1]: As you might guess, I’m a fan of Edward Tufte’s The Visual Display of Quantitative Information.