Variable Valency - Definition, Examples, Elements, FAQs

Define Variable Valency

An element's valency is its ability to combine with other elements. The valency of an element is the amount of electrons provided or absorbed by an atom in order for it to have the electronic configuration of the nearest noble gas.

Valency Varieties:

1. Ionic compounds' valency

2. Covalent substances' valency

3. Variable valency

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Variable Valency

Variable valency is shown by some items have more than one sort of valency. These compounds have one valency in one compound different valency in another. For example, iron has a valency of 2 in some compounds, such as ferrous sulphate (FeSO₄), and a valency of 3 in others, such as ferric chloride (FeCl₃). There are two sorts of valencies in copper: 1 and 2. Mercury has two valency types: 1 and 2.

What is Variable Valency?

The valency of the same element might alter due to different conditions in which a chemical reaction takes place. As a result, metals such as lead, tin, copper, mercury, iron, and others have varying valency. Metals donate electrons from their valence shell to generate positively charged ions in most cases. Some metals, on the other hand, lose electrons from the shell next to the valence shell. The element has more than one electropositive valency in this case. Variable valency is a term used to describe such elements with variable valency. Valency of mercury or Valency of Hg is +1 an +2.

Why do Elements Exhibit Variable Valency?

Consider the following iron example:

Iron is a metal (Fe)

Iron has an atomic number of 26.

Electronic configuration of iron = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

The electrical arrangement of 4s² 3d⁶ makes iron an unstable molecule. The two electrons in the 4s orbital will be eliminated first. Then iron's electrical configuration changes to 4S⁰ 3d⁶. The electronic configuration 3d⁶ is not stable.

The d subshell will become a half-filled subshell after losing one electron. This 3d⁵ electronic arrangement is stable. As a result, the element iron has two and three valencies. Iron variable valencies are the names given to these valencies. To achieve stability, the elements have varying valency. The half-filled subshell has greater exchange energy, lowering the compound's energy even further.

As a result, the compound is more stable.

Also read :

• NCERT notes Class 11 Chemistry Chapter 3 Classification of Elements and Periodicity in Properties
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Elements Having Variable Valency

Valency of cupric which is valency of Cuprous or cuprous valency (Cu⁺²) and cupric (Cu⁺³) are two types of copper (Cu).

Iron (Fe) is divided into two types: ferrous (Fe⁺²) and ferric (Fe⁺³).

Mercurous (Hg ⁺¹) and mercuric (Hg ⁺²) are two types of mercury.

Argentous (Ag⁺¹) and argentic (Ag⁺²) are two types of silver (Ag).

Stannous (Sn⁺²) and Stannic (Sn⁺³) are synonyms for Stannum (Sn).

The element with the lowest valency will be suffixed with the word "ous." The element with the highest valency will be suffixed with "ic."

Variable Electrovalency

The number of electrons lost or acquired by an element's atom during the creation of ionic bonds is its electrovalency. Variable valency is not displayed in the s-block elements. P-block elements with higher atomic numbers and inner transition elements, on the other hand, have variable valency.

There are two basic reasons why variable valency is seen

1. The effect of an inert pair in p-block elements.

2. In transition elements, there is a small energy difference between ns and (n-1)d sub shells, and ns and (n-2) sub shells in inner transition elements.

NCERT Chemistry Notes:

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Determination of Elements' Valencies from Compound Formulas

We know that chlorine (Cl) has a valency of 1.

The valency of sodium (Na) in sodium chloride (NaCl) is 1.

Calcium (Ca) has a valency of 2 in calcium chloride (CaCl₂).

The valency of iron (Fe) in ferric chloride (FeCl₃) is 3.

The valency of phosphorus (P) in phosphorus trichloride (PCl₃) is 3.

The preceding example proposes a simple rule for assessing the valency of components in two-element compounds.

The number of valency units in all the atoms of one element equals the number of valency units in all the atoms of all the other elements.

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• NCERT Exemplar Class 11th Chemistry Solutions
• NCERT Exemplar Class 12th Chemistry Solutions
• NCERT Exemplar Solutions for All Subjects