7#$  eeeees   xC cf*xef{ffffffffCHEMISTRY REVIEW FOR GEOLOGY 141 Most if not all of you have had some introduction to basic chemical notation in the past. This is intended as a review for you, but more importantly as a summary for those students who have NOT had such an introduction. (A more thorough discussion will be found in your text, pp. 37-41; if you have not had at least high school chemistry, you are strongly urged to read this very carefully.) As most of you probably realize, all matter in the world is made up of atoms, and all atoms are of particular fundamental kinds of things called elements. There are 91 naturally occurring elements, of which only a small handful are common enough to be significant at our level of study. These elements occur in the environment in combinations called compounds. Each individual combination of atoms is called a molecule. Chemists long ago devised a shorthand notation which made it simple to describe a molecule which had various numbers of atoms of different elements in it. To begin with, each element has its own one- or two-letter abbreviation. (In cases of two-letter abbreviations, the first letter is always capitalized while the second is lower-case. One-letter symbols are always capital letters.) Oxygen, for example, is symbolized by O, carbon by C, iron by Fe, etc. To indicate the number of atoms of an element in a particular molecule, a subscript number is used. Thus, simple water may be abbreviated as H2O, indicating a compound in which each molecule is composed of two atoms of hydrogen and one of oxygen. The mineral hematite, Fe2O3, likewise is a naturally occurring compound in which each basic unit is composed of two atoms of iron and three of oxygen. The most important elements in geology, with their abbreviated symbols and relative abundance in the Earth's crust, are: Oxygen O 47.0% of crust [by weight!] Silicon Si 27.2% Aluminum Al 8.1% Iron Fe 5.0% Calcium Ca 3.6% Sodium Na 2.8% Potassium K 2.6% Magnesium Mg 2.1% Titanium Ti 0.4% Manganese Mn 0.1% Phosphorus P 0.1% Hydrogen H 0.1% Carbon C 0.04% Sulfur S <0.1% In addition to basic elements, there are groups of atoms which, while not stable alone, tend to "travel" together as a package and which occur repeatedly. These are called radicals. The most common ones we will see in geology include: Carbonate CO3 Phosphate PO4 Sulfate SO4 Minerals that have the carbonate radical as part of their chemical formula (i.e., the shorthand notation for that compound) are the carbonate minerals. An example would be calcite, CaCO3. Those that have the sulfate or phosphate radicals are sulfate or phosphate minerals, respectively. Examples of these would include gypsum [CaSO4.2H2O] and turquoise [CuAl6(PO4)4(OH)8.4H2O]. vy|I`0h.*b `2N ;}