A Homologous series (Greek: homo, the same ', logos, meaning ') is a range of substances that can be represented on a general molecular formula, and at which a substance in this series from the previous material by " adding " another " chain link " is formed. The concept of homologues series was introduced in 1843 by Charles Frédéric Gerhardt and detected by Jean Baptiste Dumas for organic carboxylic acids and alcohols by measurement of physical properties. The chemical properties of the homologous series forming compounds are similar. The chemical and physical properties vary systematically with the chain length. For example, changes with the increase in the chain length of the molecules, the melting and boiling points, and the viscosity (usually increasingly parallel ). The solubility over other media subject to change.
The homologous series of alkanes is best known, however there are several other series.
Homology as structural similarity
The term homologue is also sometimes used outside of the concept of homologues series and then referred to substances that are similar in their chemical structure and, consequently, are similar in their properties. This is often also used for the chemical elements in the same Group of the Periodic Table. The elements that are under the element in question are referred to as higher homologues, those over the element as a lighter homologues.
Examples of homologous series
- Phosphines ( PnHn m (n = integer, M = 2, 0, -2, -4, -6, ...))
- Silanes ( Si n H 2n 2)
- Boranes ( BnHm (n, m = an integer) )