Molecular Compounds: Formulas and Nomenclature

Molecular compounds are formed by atoms of two or more nonmetallic elements via covalent bonds. However, the same elements may combine in different ratios, giving rise to different molecular compounds. Hence, each molecular compound is described using distinct chemical formulas and systematic naming based on the number of atoms of its constituent elements.

A binary molecular compound is represented by first indicating the more metal-like element situated to the left and bottom of the periodic table. The more nonmetallic element is denoted subsequently. Numerical subscripts signify the number of atoms of each element.

These binary molecular compounds are named using a format beginning with a Greek-prefix indicating the number of atoms of the first element, followed by the element name. The prefix 'mono-' is usually omitted for the first element. 

A second Greek-prefix denotes the number of atoms of the second element, which is followed by the element base-name ending with the suffix ‘-ide'. Hence the two different molecular compounds of carbon and oxygen, CO₂ and C₂O, are named carbon dioxide and dicarbon monoxide, respectively.

Acids, which are hydrogen-containing molecular compounds that dissociate into hydrogen plus ions and anions in water, follow a similar nomenclature. The formula of acids denotes the hydrogen first, followed by the nonmetal elements. Acids can be categorized as binary acids or oxyacids, depending on their constituent elements. 

Binary acids are composed of hydrogen and a nonmetal. The nomenclature uses the term ‘hydro', followed by the nonmetal base-name ending with the suffix ‘-ic’, and concludes with the term ‘acid’. The binary acid, HF, is named hydrofluoric acid.

Oxyacids, on the other hand, contain hydrogen and an oxyanion composed of a nonmetal and oxygen. The names of oxyacids depend on the ending-suffix in the oxyanion name. For oxyanions ending with ‘-ate’, the format uses the base-name of the oxyanion, followed by the suffix ‘-ic’, ending with the term ‘acid’. The oxyacid containing hydrogen-ions and acetate-ions is named acetic acid. For oxyanions ending with ‘-ite’, the format uses the base-name of the oxyanion, followed by the suffix ‘-ous’, ending with the term ‘acid’. The oxyacid containing hydrogen-ions and sulfite-ions is named sulfurous acid.