Naming and Writing Formulas for Molecular Compounds One milligram of gold is worth only about one cent, but one kilogram of gold is worth approximately $12,500. The correct prefix ( milli- or kilo-) makes quite a difference! Prefixes are important in chemistry, too. The prefixes in the name of a binary molecular compound tell you its composition.

Carbon and oxygen combine to form carbon monoxide (CO) and carbon dioxide (CO2), but these two invisible gases are very different. Carbon monoxide is an invisible, gaseous compound of carbon and oxygen. It is a toxic product of incomplete burning, such as occurs in automobile engines and faulty furnaces.

A prefix tells how many atoms of each element are present in one molecule. Number mono- 1 hexa- 6 di- 2 hepta- 7 tri- 3 octa- 8 tetra- 4 nona- 9 penta- 5 deca- 10 carbon monoxide (CO) carbon dioxide (CO2)

Molecular Naming Rules: Name the elements in the order listed in the formula. Use prefixes to show the number of each atom. The suffix of second element is -ide. No prefix mono- for first element. CCl4 N2O SO3 H2O

Silicon carbide is a hard material like diamond Silicon carbide is a hard material like diamond. The name silicon carbide has no prefixes, so the subscripts of silicon and carbon must be one. Thus, the formula for silicon carbide is SiC.

Quick Quiz! 1. Which of the following compounds is named INCORRECTLY? CS2, carbon disulfide BCl3, boron trichloride IF7, iodine heptafluoride PCl5, phosphorus hexachloride

Quick Quiz. 2. Which of the following molecular compounds is named INCORRECTLY? AsCl3, arsenic trichloride C2O5, dicarbon pentoxide CF4, carbon tetrafluoride H3As, hydrogen arsenide

Quick Quiz. 3. The correct formula for tetraphosphorus trisulfide is P3S4 S3P4 P4S3 S4P3