1. 2.7 Chemical Symbols and Formulas All elements on the periodic table have symbols that are recognized world wide. It does not matter which country you’re in or the language you speak; the element Iron is always identified by “Fe” and Oxygen is “O”. The names are not always the same but the symbols are. Fe is iron in Canada, fer in France and fier in Romania.

2. Chemical Symbols and Formulas Alchemists in the middle ages were among the first to recognize that it would be convenient to represent chemical substances using symbols. In 1808, the English chemist, John Dalton, developed a system of symbols to represent many elements and compounds. –Scientists found Dalton’s system too difficult to use.

3. Chemical Symbols and Formulas Today, a common set of symbols for elements is accepted around the world. A chemical symbol is an abbreviation of the name of an element. The names and symbols for elements come from many sources. –Hydrogen comes from the Greek word for “water- former.” –Mercury was named after a Roman God but the symbol, Hg, comes from the Latin word Hydrargyrum for “liquid silver.”

4. Chemical Symbols and Formulas Single symbols are used to represent elements. Combinations of symbols are used to represent compounds. These combinations are called chemical formulas. The chemical formula indicates which elements are present and in what ratio.

5. Chemical Formulas - examples Calcium Carbonate(chalk) - CaCO 3 Sodium Chloride(salt) - NaCl Acetylsalicylic acid (aspirin) - C 9 H 8 O 4 Acetic acid (vinegar) - C 2 H 4 O 2 Special notes: –Each symbol in a formula represents an element. –If only one atom of an element is present in the compound, no subscript is used. –If more than one atom of an element is used, then the symbol is followed by a number indicating how many atoms are used. This is called the subscript.

6. Homework Answer questions 2,3,4,and 5 on page 59.