Molecular Formulas - Lecture notes 4 PDF

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Nomenclature: Writing Chemical Formulas for Molecular Compounds Binary Molecular Compounds: For most simple binary molecular compounds, the subscripts needed in the formula are given by the numerical prefixes in the name. A prefix always refers to the element name that is it part of. Prefixes are needed for molecular compounds because a given set of elements may have multiple ways of combining. If you don’t yet know the number prefixes used for chemical compounds, see the "Reference Sheet for Chemical Nomenclature" for tables of prefixes. Examples: carbon monoxide vs. carbon dioxide: Here: the “mono” and “di” refer to 1 and 2 oxygen atoms, respectively:: CO = carbon monoxide, CO2 = carbon dioxide The number prefix comes before and is “attached to” the element that is applies to tetraphosphorous hexoxide Here, the “tetra’ refers to 4 phosphorous atoms and the “hex” denotes 6 oxygen atoms: P4O6 = tetraphosphorous hexoxide Since these formulas give the actual counts for each atom of each element in the molecule, these are called molecular formulas. When using molecular formulas, we DO NOT reduce the subscripts to the lowest possible ratio Common Names: Many small inorganic compounds have common names since they were known for a long time before a systematic method had been worked out. N2O is dinitrogen monoxide and has the common name nitrous oxide NO is nitrogen monoxide and has the common name nitric oxide These compounds are often referred to using common names, but the systematic name is also acceptable. Some compounds ALWAYS use a common name and never a systematic name: H2O = water and NEVER dihydrogen monoxide NH3 = ammonia and NEVER nitrogen trihydride CH4 = methane and NEVER carbon tetrahydride C 3H8 = propane and NEVER tricarbon octahydride C 2H2 = acetylene and NEVER dicarbon dihydride *NOTE = there are millions of CxHy compounds and derivatives. These are ‘organic compounds” and have their own naming system. This is covered in CHEM 106. We may encounter a select few and will just learn the names of those compounds as is necessary....