Valency

Valency is a measure in chemistry that describes the power of an element to combine with other elements. The concept is closely related to the theory of chemical bonding, the process by which atoms or ions are linked by chemical bonds to form a more complex structure such as a molecule or crystal.

History

The concept of valency was first proposed in the mid-19th century by Edward Frankland, who suggested that elements have a fixed capacity for combining with other elements. This idea was further developed by other chemists, including Archibald Scott Couper and August Kekulé, who introduced the concept of structural formulas to represent the arrangement of atoms in molecules.

Determination of Valency

The valency of an element is determined by the number of electrons in its outermost shell, also known as the valence shell. Elements with one or two electrons in their valence shell are usually metals, while those with five, six, or seven electrons are typically nonmetals. Elements with a full valence shell, such as the noble gases, have a valency of zero and are generally unreactive.

Types of Valency

There are two types of valency: normal (or principal) valency and secondary (or subsidiary) valency. Normal valency refers to the capacity of an atom to directly combine with other atoms, while secondary valency refers to the number of atoms or groups that an atom can coordinate in a complex compound.

Valency in Organic Chemistry

In organic chemistry, the concept of valency is used to predict the structure and reactivity of organic compounds. For example, carbon has a valency of four, which means it can form four bonds with other atoms. This property is the basis for the vast diversity of organic compounds.

See also

• Covalent bond
• Ionic bond
• Metallic bond
• Valence electron
• Valence (chemistry)

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