Question

what is variable valency​

Answer 1

Answer:

Certain elements combine with other atoms, donating, accepting or sharing electrons in different proportions depending on the nature of the reaction. For example, iron combines with oxygen to form ferrous oxide as well as ferric oxide. This is termed variable valency.

Answer 2

Certain elements combine with other atoms, donating, accepting or sharing electrons in different proportions depending on the nature of the reaction. For example, iron combines with oxygen to form ferrous oxide as well as ferric oxide. This is termed variable valency.

Sometimes, because of different conditions under which a chemical reaction takes place, the valency of the same element changes. Thus metals like lead, tin, copper, mercury, iron etc exhibit variable valency.

Normally, the metals donate electrons from their valence shell, so as to form positively charged ions. However, some metals lose electrons from the shell next to the valence shell. In such a situation the element exhibits more than one electropositive valency. Such elements are said to have variable valency.

Variable Electrovalency

The electrovalency of an element is equal to the number of electrons lost or gained by its atom during the formation of ionic bonds. The s-block elements do not show variable valency. However, p-block elements with higher atomic number transition and inner transition elements show variable valency.

There are two main reasons for showing variable valency

• Inert pair effect in p-block elements.
• Small energy difference between ns and (n-1)d sub shells in transition elements and ns and (n-2) sub shells in inner transition elements.

Variable Valency Examples

Certain elements have more than one valency. They exhibit variable valency. For example, copper, tin, iron and mercury exhibit variable valency. Copper combines with oxygen to form cuprous oxide (Cu2O) and cupric oxide (CuO).

Valency of oxygen being two, combining capacity of copper in the first case is one and that in the second case is two. The suffix “ous” is used to indicate the lower valency and the suffix “ic” to indicate the higher valency. The following table gives the names of some compounds with variable valencies of elements.

Determination of Valencies of Elements from the Formula of Compounds

We know that the valency of chlorine (Cl) is 1.

• In sodium chloride (NaCl), the valency of sodium (Na) is 1

• In calcium chloride (CaCl2), the valency of calcium (Ca) is 2.

• In ferric chloride (FeCl3), the valency of iron (Fe) is 3.

• In phosphorus trichloride (PCl3), the valency of phosphorus (P) is 3.