AtomixQuest

AtomixQuest turns the periodic table into a daily quiz. Every round deals a few element cards and asks one question about them: which has the highest atomic mass, which is the least dense, which has a melting point closest to a given number. The daily puzzle mixes Maximum, Minimum and Target rounds with a Wildcard round whose rule changes from day to day. The properties range from the familiar (atomic number, group, period, discovery year) to the specialist (ionization energy, specific heat, number of natural isotopes), and each comes with a short tip explaining the unit.

It is made by the same developer, C3-Peyo, as HeatmapQuest, CrossmapQuest and HistoriaQuest, and shares their system: points for each round, a streak that raises your score by 2% a day up to 25%, shields that protect a streak for one missed day, leaderboards, leagues and an archive of earlier puzzles. A weekly Survival run, one attempt a week that resets every Wednesday, sits beside the daily one. Past days can be replayed from the archive, though they add no points or streak. Leagues let you rank against colleagues, friends or family with an invite code.

It suits students, teachers and anyone who once learned the table and wants to see how much stuck. The data comes mostly from Wikipedia and public databases, as the site notes.