I'd like to announce a new Labs tool to show a periodic table.
It is based on WikiPeriod's PHP code (in turn ported from JavaScript) and features several improvements:

• 'tiles' are wider and taller;
• most of them are now provided with a background color (the same as Wikipedia's) based on the elements' "subclass of" property (the same that powers period/group detection);
• for labels, Wikidata's built-in language fallback is used instead of just falling back to English;
  
• a public JSON API is available for everyone!
  

And some more under the hood:

• rewritten in Python with Jinja2:
• more object-oriented
  
• presentation is split from actual logic
• less vulnerable to XSS attacks
• a LRU (least recently used) cache with a maximum TTL (per-item time-to-live) value of 6 hours is used to avoid hitting data sources on every request;
  
• both the Wikidata API and Wikidata Query can be used interchangeably as sources.

I had to create some items such as Q19753344 and Q19753345 to properly categorize elements. My knowledge of chemistry is limited, so please report/fix every mistake you can find ;-)

Future plans include:

• oxidation state
• images
• responsive design
  
• alternative table structures