Definition Of Valency

Definition Of Valency

Valency is the combining capacity of an element

More About Valency

  • It is a common belief that that the valences of the elements are those which can be derived by looking at the Groups (columns) of the Periodic Table
  • It is true that these are the most common valences, but the real behavior of electrons is less simple
  • valence, also known as valency or valence number, is the number of valence bonds a given atom has formed, or can form, with one or more other atoms
  • For most elements the number of bonds can vary
  • The IUPAC definition limits valence to the maximum number of univalent atoms that may combine with the atom, that is the maximum number of valence bonds that is possible for the given element
  • The valence of an element depends on the number of valence electrons that may be involved in the forming of valence bonds
  • A monovalent atom, ion or group has a valence of one and thus can form one covalent bond
  • The valency of an element is the number of electrons present in outermost orbit of that element
  • The outermost shell of an atom can accommodate a maximum of 8 electrons
  • The elements having 8 electrons in the outermost shell show little chemical activity. Helium has two valence electrons
  • The combining capacity or valency is zero for those elements
  • Thus, the valency of an element is explained as its tendency to attain octet configuration
  • Atoms would react to attain an octet configuration, that is, stable configuration, by gaining, losing or sharing electrons
  • The number of electrons lost, gained or shared would give us the valency of the element or the combining capacity of the element
  • For example, hydrogen/lithium/sodium atoms contain one electron each in their outermost shell; therefore each one of them can lose one electron. So they are said to have a valency of one
  • Similarly, the valency of magnesium and aluminium is two and three respectively as magnesium has two electrons and aluminium has three electrons in its valence shell
  • If the number of electrons in outermost shell of elements is close to octet, then its valency is determined by subtracting the number of electrons from eight
  • Thus, the valency of fluorine is one and that of oxygen is two

Applications:

  • If the valence shell is full, then the element is inert
  • If the valence shell isn't full, then the element is reactive, which means that it can form a bond with an atom of another element. Each atom shares its valence electrons in an attempt to complete its own valence shell
 

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