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Chemical Formulas and Equations Chapter 9 – 2 Part 1 Chemical Formulas • A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance. C6H12O6 Glucose • A subscript is a number written below and to the right. – It tells how many atoms are in this molecule. – If there is no subscript, then there is just one atom. Some Basic Rules • When you have two elements, you have two words in the name • The first word is the first element. • The second word is the second element. Continued • The second word also ends in “IDE”. • Like oxygen becomes oxide. Writing Formulas for COVALENT COMPOUNDS • Covalent compounds are often composed of nonmetals. • The names of many covalent compounds use prefixes. • Example: Carbon Dioxide & Dinitrogen monoxide CO2 N2O Here are the first ten prefixes: Prefixes Used in Chemical Names Mono1 Hexa6 Di- 2 Hepta- 7 Tri- 3 Octa- 8 Tetra- 4 Nona- 9 Penta- 5 Deca- 10 Writing Formulas Covalent Compounds • Use the name of compound to write its formula • Ex: Carbon Dioxide • No prefix on first atom indicates 1 atom • The prefix di indicates 2 oxygen atoms= CO2 • Prefixes always used on second atom C0 = carbon monoxide • What is the formula for dinitrogen trioxide? • ––> N2O3 More Practice • • • • • • • • 1. 2. 3. 4. 1. 2. 3. 4. Dihydrogen monoxide Silicon dioxide Carbon monoxide Hydrogen bromide H2O SiO2 CO HBr • • • • • • LET’S TRY IT! SiF4 Silicon tetrafluoride SF6 Sulfur hexafluoride N2O5 Dinitrogen pentaoxide