How the Periodic Table Challenge Works
The Periodic Table Challenge is an interactive teaching resource with a blank periodic table and three modes. Instant gives feedback as you work. Hardcore waits until you submit the completed table and gives a total score only. Novice also waits until submission, then identifies correct and incorrect entries. These originally ran as separate cgi files and in 2026 I modernized this to run entirely in the browser.
I designed the Classic Version for my upper division courses in which the student must know the periodic table. I didn't say "memorize", although that's what it may appear to be. But in order to write essays you have to know the alphabet, right? If you are attending a chemistry seminar and someone mentions an iron-containing compound, you have to know that Fe is in 8th column over, has some chemistry similar to Ru and has 5 d-electrons if it is in the 3+ valence state.
Hardcore and Novice (submission modes)
- Fill all 118 answer boxes before selecting Submit answers. While you work, the panel shows how many boxes are filled and your elapsed time. It does not reveal correctness, hints or capitalization corrections. Entries stay in the browser and are not submitted to a server.
- Submit answers compares each entry with its element symbol, ignoring capitalization, and stops the timer. Hardcore reveals only the total score. Novice also marks the entries correct or incorrect, without supplying missing answers. You can edit the same entries and resubmit without starting over. Editing hides the previous score and clears review marks until the next submission. Start Over is available when you want a completely fresh attempt.
Instant mode
Instant mode checks each entry as you work. The JavaScript routine checks your answer and adjusts your score when you leave an answer box. Two-letter entries automatically advance to the next box; for one-letter entries, press Tab or Enter, or tap another box. You can choose to advance across rows or down columns. Correct answers use the standard element-symbol capitalization. If your answer is wrong, the script replaces the wrong answer with a "*" so you can identify which ones are not yet correct.
In addition, this version sports an auto-hints feature. When this is turned on, three incorrect attempts on an element reveal a dismissible hint card in the table's blank space between Be and B. The hint identifies the atomic number shown in the lower-right corner of the answer box. For two-letter symbols, it gives the first letter; for one-letter symbols, it tells you that the symbol has one letter. Close the hint with its × button or Escape, or continue typing.
All modes have the option to advance by row or column as you work and will automatically advance after entering two letters. Changing modes after entering answers opens a confirmation if you want to switch modes because this will reset the table. Start Over keeps the current mode and advance preferences. A comment based on your score appears automatically in the table’s hint area after submission or when Instant is completed.
Another nice touch in this version is that it tells you the number of incorrect attempts you have made. After all, anyone can get all 118 elements, but only the best will do it without making any mistakes. I have also added a timer which stops when the table is correctly completed. This enables our visitors to have a contest to see who can complete the table with the fewest errors in the shortest amount of time. To make the determination of a winner fair, I suggest adding a predefined time penalty (5 or 10 seconds) for each incorrect answer; this is a feature I can add at a later date.
- October 15, 2026 — A vast update that modernized the Easier Instant Version with a larger desktop table, a fixed-width table that scrolls on phones, darker element colors, and atomic numbers. Correct answers now autocorrect to standard capitalization. Two-letter entries now advance automatically, with a choice of across-row or down-column order. Hints have moved to a dismissible card between Be and B instead of using popup dialogs. I implemented intuitive score, timer and reset controls, corrected the timer to stop at all 118 elements, and refreshed this explanation page and its markup. And I brought back the Classic Version incorporating all three modes into one page; a mode change clears progress and has a confirmation popup.
- February, 2023 - We switched to a new server which meant the form that we used to handle the Classic version broke.
- September 3, 2018. 2.2b.4 - Added Nh, Fl, Mc, Lv, Ts, and Og. There's really not much point to having these elements here except for completeness sake. It's not like we do any chemistry with them. Still, they do make for good trivia questions and add to our alphabet for making clever t-shirts using elemental symbols
- July 27, 2010. 2.2b.3 - Added a Start Over feature to the Easier Instant Version. This resets the scores, table, and timer back to zero, alleviating some obscure keystrokes that Firefox required. Also changed the timer to start when you enter your first answer rather than when the page loads
- July 13, 2010. 2.2b.2 - Finally got around to adding Ds, Rg, and Cn...not like you can put any of these in a vial, though
- March 12, 2007. 2.2b.1 - fixed score/time display issue in Easier Instant Version with Firefox
- September 10, 2004. Version 2.2a (Challenging Classic Version) and 2.2b (Easier Instant Version. For some unknown reasons, the original AppleScript grading application (see below) stopped working correctly. It appeared to be some sort of bizarre permissions issue or else a conflict with a recent software or OS upgrade. Therefore, I had to rewrite the grading routine using JavaScript. I made two versions of this because a) I saw a need for an "easier version" and b) the new Easier Instant Version can be saved to disk, enjoyed while off-line, and includes some cool new features
- November 9, 2003. Version 2.1 released. We upgraded to a dual 1 GHz G4 server Mac OS X. This forced us to replace the Hypercard grading stack with an AppleScript application because, for reasons nobody understands, Apple Computer elected to never release a Mac OS X-compliant version of HyperCard.
There are no fundamental changes in this version, although the grading response should be noticeably faster
- June 9, 2000. Version 2.0.2. Moved from the U of KY web site to ILPI. Different comments are now included for each score. Put a box around the entire table. Added the IUPAC-approved names for elements up to 109 (up from 103)
- October 11, 1999 Version 2.0.1. Made sure an HTTP header is sent with the reply, correcting an error with certain browser/firewall combinations. Fixed a few typos in the hints
- May, 7, 1999. Version 2.0 debuted. As originally designed, the Periodic Table Challenge did not inform you which elements were correct and incorrect. I prefer this method because it provides additional review by making you figure out which elements are incorrect. However, in Version 2.0 you know have the option of checking the Novice Mode box to reveal your errors. This could be useful when you are first starting out or if you are practicing but don't have a periodic table to consult
- June 27, 1997. I added a feature which allows you to ask for one random hint or piece of trivia with your score. Some day in the future I'd like to program in a way of returning hints such as "you are missing the element named for the god called Tantalus" or "you have the most radioactive element where the largest element should be" etc., but that's a lot more work. [Edit: I did eventually add that]
How well do people like the PTC? Here are some examples. If you have kudos or comments, send them along to us. We'd love to hear them and maybe we'll even post them here.