Chemical Elements
A few examples of what you can ask Wolfram|Alpha about:
get information about a chemical element
specify an element by symbol
specify an element by atomic number
compare several elements
Element Properties
request a property of a chemical element
compare properties of multiple elements
request a particular class of data about an element
do computations using properties of chemical elements
Classes of Elements
get information about a class of chemical elements
compare properties of a class of elements
find elements meeting given criteria
plot a property for a class of elements
compare classes of elements