Purdue University
Purdue University: Elements, Compounds & Mixtures
Provides definitions and characteristics of elements, compounds, and mixtures, and gives an animated image of each.
Encyclopedia of Earth
Encyclopedia of Earth: Physics & Chemistry: Calcium
Information about the element, Calcium, atomic number 20. Covers physical and atomic properties, sources, its role in geochemical cycles, how abundant it is on the Earth, its isotopes, some compounds of calcium, and its importance to...