Valencia or valence number , in chemistry , is the word that identifies the figure that accounts for the possibilities of combination that an atom has with respect to others to achieve a compound. A measure related to the number of chemical bonds that the atoms of a chemical element establish .
Summary
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- 1 Origin of the term
- 2 Introduction
- 3 History
- 4 Types of Valencia
- 5 Sources
Origin of the term
- It comes from the Latin “valentia”, which has meanings such as strength and capacity, preparation or extract.
Introduction
In the field of chemistry, it refers to the combining power of an element, a concept registered since 1884 . Once the constitution of the substances has been determined and its formula is found, it is found that all bodies are made up of groups of atoms joined together by forces strong enough so that these aggregates can be considered as independent structural units.
Only noble gases and metals in the vapor state are made up of isolated atoms. The force that exists between two atoms, whatever their nature, constitutes a chemical bond .
History
- 1789. The first drawings on combinations of what were known as last particles published. Made by William Higgins , and in them reference was made to the concept of valence bonds.
- 19th century, late; The concept of valence was developed when trying to make the topic of chemical formulas of different chemical compounds more rational.
- 1852. By the work, fundamentally, of Frankland , Kekulé and Butlerow the first attempts of representation of the bodies occur and with it the introduction in the chemistry of the concept of the valence; for many years, the valences of the atoms that made up the compounds were represented by traces or lines of connection between them, without knowing each other and without prejudging their nature.
- 20th century. The concept of valence underwent an evolution with which it was possible to describe the concept of chemical bond more accurately :
1916 , the Lewis structure or concept of electron pair bonding, in which two atoms can share one and six electrons, forming the bond of a single electron, single bond, double bond, or triple bond. In Lewis’s own words: “An electron can be part of the sheaths of two different atoms and cannot be said to belong to one exclusively.
The same year, Walther Kossel launched a theory similar to Lewis’s, with the difference that his model assumed a complete transfer of electrons between atoms, making it an ion bond model.
Both Lewis and Kossel structured their link models from Abegg’s rule (1904)
1928 , the theory of molecular orbitals .
In 1919 , Irving Langmuir took the term valence to explain Lewis’ cubic atom model , stating that the number of even electrons that any atom can have when sharing with the atom next to it is known as the covalence of the atom.
The prefix “co-” of covalence means “together”, so a co-valent bond means that the atoms share valence.
Example: if an atom has valence +1, it means that it lost one electron, and another atom, with a valence -1, means that they have one more electron. So a bond that forms between two atoms occurs because they complement or share their trends in the balance of valences.
Therefore, it is more correct to speak of covalent bonds, rather than simply using the word valence.
- 1994. The IUPAC (International Union of Pure and Applied Chemistry), after many attempts to give a single definition, adopted the following:
“The maximum number of univalent atoms that can be combined with one atom of the element in
consideration, or a fragment, or for which an atom of this element can be replaced ”.
Types of Valencia
- Maximum positive Valencia: positive digit that reflects the highest ability of an atom to combine and that is the same for the group that corresponds to it in the Periodic Table of the Elements
Example: Chlorine belongs to group VII of the periodic table and therefore its positive (maximum) valence is equal to 7.
- Negative Valencia: negative digit that shows the possibilities of the atom to be combined with another that appears with a positive valence. This negative number can be found by counting what is missing from the maximum positive valence to arrive at number 8, but always with a negative sign.
Example: Chlorine has a maximum positive valence of 7, and if we subtract 8, it will give us -1, with that negative number being the maximum negative valence for this element.
