Homologous series

A homologous series (Greek: όμό 'equal', λογος 'sense') is a series of substances that can be represented using a general empirical formula and in which a substance in this series is derived from the previous substance by “adding” another “chain link “Is formed. The concept of the homologue series was introduced in 1843 by Charles Frédéric Gerhardt and proven by Jean Baptiste Dumas for organic carboxylic acids and alcohols by measuring physical properties. The chemical properties of the compounds making up the homologous series are similar. The chemical and physical properties vary systematically with the chain length. For example, as the chain length of the molecules increases, the melting and boiling points and the viscosity change (usually increasing in parallel). The solubility properties in relation to other media can also change.

The homologous series of alkanes is particularly well known, but there are also various other series.

Homology as structural similarity

The term homolog is sometimes used outside of the term homologous series and describes substances that are similar in terms of their chemical structure and consequently also have similar properties. This is also often used for the chemical elements in the same group of the periodic table . The elements below the element in question are referred to as higher homologues , those above the element as lighter homologues .

Examples of homologous series

n and m are each whole numbers.

Organic chemistry

Hydrocarbons

• Alkanes (C _n H _{2 n +2} )
• Cycloalkanes (C _n H _{2 n} )
• Alkenes (C _n H _{2 n} )
• Alkynes (C _n H _{2 n −2} )

Carboxylic acids and perfluorocarboxylic acids

• Monocarboxylic acids (C _n H _{2 n} O ₂ )
• Perfluorocarboxylic acids (C _n F _{2 n +1} COOH)

Inorganic chemistry

Hydrides

• Phosphanes (P _n H _{n + m} , m = 2, 0, −2, −4, −6, ...)
• Silanes (Si _n H _{2 n +2} )
• Boranes (B _n H _m )

Oxides

• The elements of the nitrogen group form both the homologous series of the trioxides N ₂ O ₃ , P ₂ O ₃ , As ₂ O ₃ , Sb ₂ O ₃ and Bi ₂ O ₃ , and the series of the oxides N ₂ O ₅ , P ₂ O ₅ , As ₂ O ₅ , Sb ₂ O ₅ and Bi ₂ O ₅ .

Individual evidence

1. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 551.

Web links

Commons : Homologous series  - collection of pictures, videos and audio files