Upside Down Periodic Table

Different point of view? Recently the journal Nature Chemistry published a short article by Poliakoff et al. suggesting flipping the Periodic Table upside down. For the sticklers of symmetry operations, technically you are rotating 180 degrees about a horizontal axis.

The authors suggest several reasons to do this. If you’re used to a typical x–y two-dimensional graph, the origin starts at the lower left. Numerical values therefore increase both rightward and upward. The way electrons are ‘filled’ using the aufbau principle suggests a building up from lower to higher energy ‘orbitals’. And if you happen to be a kid, and there’s a periodic table in your classroom hung up on the wall, the elements you’re most likely to encounter would be closer to eye-level rather than way up there closer to the ceiling. Also, “looking at a problem from a new viewpoint often gives rise to new ideas, so this orientation of the table will undoubtedly give us all a new perspective.”

Other chemists were polled for their thoughts. Some liked it. Others preferred the original. For example, if you think of a data table rather than a graph, then information typically starts at the top left. As a follow-up the upside down table was then shown to non-chemists with identifying markers stripped out and eye-movement was tracked to generate heat maps of where participants spent the most time looking. I’m not sure how useful this was but the asymmetry could be interesting from a perception point of view. 6 of the 24 observers recognized the outline of a periodic table. When asked which was preferred, the conventional model won, although the upside down version was rated as more symmetrical. It sort of looks like the silhouette of a desk.

I prefer the conventional periodic table. Possibly that’s because of sheer exposure and familiarity, but I do have one argument for it. Chemistry is about making and breaking chemical bonds, i.e., moving electrons around. How electrons move around is related to how strongly they are bound to their nuclei. So it’s a question of energy. The element with the lowest ionization energy is in the bottom left corner (francium) and the one with the highest ionization energy is in the top right corner (helium). In fact, I think of the periodic table in terms of diagonal lines rather than orthogonal ones. But the elements have their idiosyncracies. The periodic table is kinky!

Coming up with the periodic table in its current form is partly due to historical contingency. There were plenty of clever ideas in the 19^th century before Mendeleev’s won out. One was a cool spiral by Hinrichs. But organizing all that data was no easy feat. I’d previously designed an Alien Periodic Table activity to give students a glimpse of the challenges faced by the early scientists. What was interesting is that students inevitably started with the least massive element in the top left corner. I suppose it comes from habit! They’re used to a particular construct of the Periodic Table, and I suppose it would take extra cognitive work to imagine starting at the bottom left. I suspect we won’t see a large-scale change towards the upside down periodic table.