Elements is a cool and searchable periodic table of elements with lots of useful information. Passing over an element on the table gives you instant access to general information. Clicking on an element gives you full information, such as crystal structure, physical properties, electron configuration with graphical diagram, and known isotopes.
Elements also contains a fast, accurate, and easy to use molecular weight calculator wich accepts classical chemical formula syntax with math symbols, and a two-way converter for volume, mass, concentration, and quantity.
update from version 2.3 available through application (Elements > Check for Updates...)