SECONDARY VALENCE Meaning and
Definition
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Secondary valence, also known as coordination number or oxidation number, refers to the number of electrons an atom can potentially accept, donate, or share in order to form stable chemical bonds with other atoms. It is a measure of the electron transfer or sharing capabilities of an element or compound in a chemical reaction. Unlike primary valence, which is determined by the number of electrons in the outermost shell of an atom and represents the maximum number of bonds an atom can form, secondary valence can vary and is influenced by factors such as electronegativity, oxidation state, and the nature of the other atoms involved.
Secondary valence is crucial in understanding the formation and stability of coordination compounds or complexes, where a central metal ion is surrounded by ligands. These ligands can be atoms, ions, or molecules that coordinate to the central metal atom through shared electron pairs in a covalent bond. The coordination number of the central metal ion indicates the number of ligands attached to it, which is determined by both the primary and secondary valence of the metal ion.
In coordination chemistry, the secondary valence of the ligand plays a significant role in determining the overall stability, geometry, and reactivity of the complex. It is often denoted by a Roman numeral in brackets following the symbol of the metal ion in chemical formulas. The determination of secondary valence is essential in predicting the properties and behavior of coordination compounds and is valuable in various applications, including catalysis, bioinorganic chemistry, and materials science.
Etymology of SECONDARY VALENCE
The etymology of the word "secondary valence" can be traced back to the Latin word "valentia", meaning strength or power. "Valentia" is derived from the Latin verb "valere", meaning to be strong or to have value.
The term "valence" itself originally referred to the combining power of an element in chemical compounds, and it was introduced by the Swedish chemist Jöns Jacob Berzelius in the early 19th century.
The term "secondary" in "secondary valence" indicates that it is an additional, or secondary, form of valence present in certain chemical compounds. This term is mainly used in coordination chemistry to describe the additional bonds formed between a central metal atom and a ligand, which are responsible for the stability and structure of coordination compounds.
