molecular formulas
The chemical formulas for covalent compounds are referred to as molecular formulas because these compounds exist as separate, discrete molecules. Typically, a molecular formula begins with the nonmetal that is closest to the lower left corner of the periodic table, except that hydrogen is almost never written first H2O is the prominent exception . Then the other nonmetal symbols are listed. Numerical subscripts are used if there is more than one of a particular atom. For example, we have already seen CH4, the molecular formula for methane. Naming binary two-element covalent compounds is similar to naming simple ionic compounds. The first element in the formula is simply listed using the name of the element. The second element is named by taking the stem of the element name and adding the suffix -ide. A system of numerical prefixes is used to specify the number of atoms in a molecule. Table 4.1 "Numerical Prefixes for Naming Binary Covalent Compounds" lists these numerical prefixes. Normally, no prefix is added to the first elements name if there is only one atom of the first element in a molecule. If the second element is oxygen, the trailing vowel is usually omitted from the end of a polysyllabic prefix but not a monosyllabic one that is, we would say monoxide rather than monooxide and trioxide rather than troxide . Table 4.1 Numerical Prefixes for Naming Binary Covalent Compounds Number of Atoms in Compound.