In this interactive object, learners calculate formula and molecular weights by working through five examples and two problems.

The definition of an isotope is illustrated using the three isotopes of carbon. The three isotopes of hydrogen are discussed as exceptions.

In this animated and interactive object, learners examine the properties of liquids, solids, and gases.

Students read about the basic organization and structure of the periodic table of elements. By clicking on the symbol, they can read that element's atomic number and weight. In an exercise, students identify elements as belonging to a group, a period, or neither.