Variable Valency

Edited By Team Careers360 | Updated on Jul 02, 2025 04:43 PM IST

In nature, elements rarely exist alone; instead, they interact with one another. The ability of one element to combine with another is known as valency. To achieve a stable state, elements interact with one another. It establishes the maximum amount of electrons an element can take or donate in order to form a stable electronic state.

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Define Variable Valency
Variable Valency
What is Variable Valency?
Why do Elements Exhibit Variable Valency?
Elements Having Variable Valency
Variable Electrovalency
Determination of Elements' Valencies from Compound Formulas

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 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.

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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

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

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NCERT Chemistry Notes:

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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Frequently Asked Questions (FAQs)

1. What is the difference between valency and variable valency?

The valence of an element is its ability to combine with other elements. The capacity of some elements to interact with other elements varies depending on the nature of the interaction; this trait is known as variable valence. For example, iron (Fe) can have valences of 2 and 3.

2. What causes variable valency in the first place?

Valence electrons are electrons that are present in an atom's outermost shell. As a result, one or more electrons from the core's outermost shell may be lost when valence electrons are removed. As a result, such items have variable valentia, indicating that they have two or more different valencies.

3. What is an example of variable valency?

Depending on the nature of the reaction, some elements combine with other atoms to donate, take, or exchange electrons in varying amounts. For starters, both ferrous and ferric oxide are formed when iron reacts with oxygen. It's known as the valence element.

4. What is the oxygen valency?

The valence value of oxygen is 2. It is an octet since it is 2,6 and only requires 2 more electrons to finish. Even though valence is equal to n for elements with n= 1,2,3, and 4 electrons in the outer shell, valence is equal to 8-n for elements with n= 5,6, and 7 electrons in the outer shell.

5. Why does phosphorus exhibit a wide range of valencies?

Because the phosphorus valence is 3, they will increase their valence due to the unoccupied d orbital. Because phosphorus has a valence shell with 5 electrons, the answer should be 3. As a result, it absorbs 3 electrons and completes its bit, because accepting 3 electrons is considerably easier than giving 5 electrons.

6. What role does variable valency play in catalysis?

Variable valency is crucial in many catalytic processes. Catalysts often work by cycling between different oxidation states, facilitating electron transfer in reactions. This is particularly important in transition metal catalysts.

7. How does variable valency impact the formation of coordination compounds?

Variable valency allows elements, particularly transition metals, to form a diverse range of coordination compounds. Different oxidation states can accommodate different numbers and types of ligands, leading to varied geometries and properties.

8. What is the importance of variable valency in electrochemistry?

Variable valency is fundamental to many electrochemical processes. The ability of elements to exist in multiple oxidation states allows for the flow of electrons in electrochemical cells, making possible technologies like batteries and fuel cells.

9. How does variable valency affect the reactivity of coordination compounds?

Variable valency significantly impacts coordination compound reactivity. Different oxidation states of the central metal ion can lead to different ligand affinities, substitution rates, and redox potentials, resulting in a wide range of reactivities.

10. Can you explain the concept of inner transition elements in relation to variable valency?

Inner transition elements (lanthanides and actinides) often exhibit variable valency due to their ability to lose f-electrons in addition to s and d electrons. This leads to a wide range of possible oxidation states and complex chemistry.

11. How does variable valency impact the naming of compounds?

Variable valency complicates compound naming. For elements with multiple valencies, the specific valency must be indicated in the compound name, usually using Roman numerals in parentheses after the element name (e.g., iron(II) chloride vs. iron(III) chloride).

12. What is the relationship between variable valency and chemical bonding?

Variable valency directly affects chemical bonding. Elements with variable valency can form different types of bonds (ionic, covalent) with varying strengths and geometries, depending on the specific valency exhibited in a given compound.

13. How does the periodic table help in understanding variable valency?

The periodic table provides information about an element's electron configuration and typical valencies. Transition metals, found in the d-block of the periodic table, are particularly known for exhibiting variable valency due to their partially filled d-orbitals.

14. Can you explain the concept of oxidation state in relation to variable valency?

Oxidation state represents the degree of oxidation of an atom in a compound. Variable valency is closely related to oxidation states, as elements with variable valency can exist in multiple oxidation states. The oxidation state reflects the number of electrons an atom has gained, lost, or shared in a compound.

15. What's the difference between valency and oxidation number?

Valency refers to the combining capacity of an atom, while oxidation number (or oxidation state) represents the apparent charge on an atom in a compound. Valency is always positive, while oxidation numbers can be positive, negative, or zero.

16. Can you provide examples of elements with variable valency?

Common examples include iron (Fe2+, Fe3+), copper (Cu+, Cu2+), mercury (Hg+, Hg2+), tin (Sn2+, Sn4+), and sulfur (S2-, S4+, S6+). These elements can form compounds with different valencies due to their electronic structures.

17. How does variable valency affect an element's reactivity?

Variable valency can significantly impact an element's reactivity. Elements with multiple valencies can form a wider variety of compounds and participate in more diverse chemical reactions, often leading to greater reactivity and more complex chemistry.

18. What are some common misconceptions about variable valency?

Common misconceptions include thinking that all elements have variable valency, that valency is always equal to the group number in the periodic table, or that variable valency only applies to metals. In reality, variable valency is specific to certain elements and depends on their electronic structure.

19. Can you explain how variable valency relates to transition metal complexes?

Variable valency is crucial in transition metal complex formation. The ability of transition metals to exhibit multiple oxidation states allows them to form a wide variety of complexes with different geometries, colors, and magnetic properties.

20. What is the significance of variable valency in biological systems?

In biological systems, variable valency plays a vital role in many processes. For example, iron in hemoglobin switches between Fe2+ and Fe3+ states during oxygen transport, and copper in enzymes utilizes its Cu+/Cu2+ variable valency for electron transfer reactions.

21. How does variable valency influence the color of compounds?

Variable valency can dramatically affect compound color, especially in transition metal compounds. Different oxidation states can result in different electron configurations, leading to varying absorption of visible light and thus different colors.

22. How does variable valency affect an element's position in the reactivity series?

Variable valency can complicate an element's position in the reactivity series. An element may show different levels of reactivity depending on which valency state it's in, potentially occupying multiple positions in the series.

23. How does variable valency affect the solubility of compounds?

Variable valency can significantly impact compound solubility. Different valency states of the same element can form compounds with varying solubilities. For instance, iron(II) compounds are generally more soluble than iron(III) compounds in water.

24. How does variable valency affect the magnetic properties of compounds?

Variable valency can significantly influence a compound's magnetic properties. Different oxidation states can result in different numbers of unpaired electrons, leading to variations in paramagnetic or diamagnetic behavior.

25. Can you explain how variable valency affects the acid-base behavior of compounds?

Variable valency can influence the acid-base behavior of compounds. Different oxidation states of an element can exhibit different acidic or basic properties. For example, manganese in different oxidation states can form compounds ranging from basic (Mn(OH)2) to acidic (HMnO4).

26. What is variable valency?

Variable valency refers to the ability of an element to exhibit different valencies (combining capacities) in different compounds. This occurs when an element can form multiple types of ions or share different numbers of electrons in chemical bonds.

27. What is the role of variable valency in the chemistry of organometallic compounds?

In organometallic chemistry, variable valency allows metals to form a variety of bonds with organic ligands. Different oxidation states can accommodate different numbers and types of organic groups, leading to diverse structures and reactivities.

28. Can you explain the concept of mixed valency compounds in relation to variable valency?

Mixed valency compounds contain an element in more than one oxidation state within the same compound. This phenomenon is a direct result of variable valency and leads to interesting electronic and magnetic properties, often seen in minerals and synthetic materials.

29. Why do some elements show variable valency while others don't?

Elements show variable valency due to their electronic configuration. Those with unpaired electrons in their outermost shell can lose or share different numbers of electrons, leading to variable valency. Elements with stable electron configurations (like noble gases) typically don't exhibit this property.

30. What role does electron configuration play in variable valency?

Electron configuration is crucial in determining an element's valency. Elements with variable valency often have electrons in different subshells (s, p, d, f) that can be lost or shared to varying degrees, resulting in different valencies.

31. How does variable valency influence the stability of compounds?

Variable valency can impact compound stability. Some valency states may lead to more stable compounds than others. For example, Fe3+ compounds are generally more stable than Fe2+ compounds due to the higher oxidation state's increased stability.

32. What is the connection between variable valency and redox reactions?

Variable valency is closely linked to redox (reduction-oxidation) reactions. Elements with variable valency can undergo redox reactions, changing their oxidation states. This property is fundamental to many important chemical and biological processes.

33. Can you explain the concept of disproportionation in relation to variable valency?

Disproportionation is a type of redox reaction where a species with an intermediate oxidation state converts to two different species, one with a higher and one with a lower oxidation state. This process is possible due to the variable valency of certain elements.

34. How does variable valency influence the formation of alloys?

Variable valency can affect alloy formation by influencing the types of intermetallic compounds that can form. Different valency states can lead to different crystal structures and properties in alloys.

35. What is the relationship between variable valency and the stability of nuclear isotopes?

While valency is primarily an electronic property, the stability of nuclear isotopes can indirectly affect an element's observed valencies. Some oxidation states may be more stable or accessible for certain isotopes due to nuclear structure effects.

36. How does variable valency impact the effectiveness of chemical analysis techniques?

Variable valency can complicate chemical analysis. Different oxidation states of an element may require different analytical techniques or react differently to the same reagents. Understanding an element's possible valencies is crucial for accurate analysis.

37. Can you explain how variable valency affects the formation of complex ions?

Variable valency allows for the formation of a diverse range of complex ions. Different oxidation states of a central metal ion can accommodate different numbers and types of ligands, leading to complex ions with varying charges, geometries, and properties.

38. What is the significance of variable valency in environmental chemistry?

In environmental chemistry, variable valency plays a crucial role in processes like metal speciation in water bodies, soil chemistry, and atmospheric reactions. The different oxidation states of elements can greatly affect their environmental behavior and toxicity.

39. How does variable valency influence the strength of chemical bonds?

Variable valency can significantly affect bond strength. Higher oxidation states generally form stronger bonds due to increased electrostatic attraction, while lower oxidation states may form weaker bonds. This impacts properties like melting point and reactivity.

40. Can you explain the concept of amphoterism in relation to variable valency?

Amphoterism, the ability of a substance to act as both an acid and a base, is often related to variable valency. Elements that can exist in multiple oxidation states may form compounds that exhibit amphoteric behavior in different chemical environments.

41. How does variable valency affect the formation of coordination polymers?

Variable valency allows for the creation of diverse coordination polymers. Different oxidation states of metal ions can lead to varying coordination numbers and geometries, resulting in a wide range of possible polymer structures and properties.

42. How does variable valency influence the stability constants of complex ions?

Variable valency affects the stability constants of complex ions. Different oxidation states of a metal ion can have varying affinities for ligands, resulting in different stability constants for complexes formed with the same ligands.

43. Can you explain how variable valency impacts the redox potentials of elements?

Variable valency directly affects redox potentials. The ease with which an element can transition between different oxidation states determines its standard reduction potential, which is crucial in predicting the direction and extent of redox reactions.

44. What is the significance of variable valency in geochemistry?

In geochemistry, variable valency influences mineral formation, weathering processes, and element distribution in the Earth's crust. The different oxidation states of elements can lead to varying solubilities and reactivities in geological environments.

45. How does variable valency affect the formation of cluster compounds?

Variable valency allows for the formation of diverse metal cluster compounds. Different oxidation states of metal atoms can lead to various bonding arrangements within clusters, resulting in a wide range of structures and properties.

46. Can you explain the concept of valence tautomerism in relation to variable valency?

Valence tautomerism involves the interconversion between two forms of a molecule that differ in the distribution of electrons. This phenomenon is closely related to variable valency, as it often involves changes in the oxidation states of metal centers in coordination compounds.

47. How does variable valency influence the spectroscopic properties of compounds?

Variable valency significantly affects spectroscopic properties. Different oxidation states can lead to varying electronic transitions, resulting in distinct absorption and emission spectra. This is particularly evident in the UV-visible and X-ray spectroscopy of transition metal compounds.

48. What is the role of variable valency in the design of functional materials?

Variable valency is crucial in designing functional materials like sensors, catalysts, and electronic components. The ability to switch between different oxidation states allows for the creation of materials with switchable properties or responsive behaviors.

49. How does variable valency affect the thermodynamics of chemical reactions?

Variable valency influences reaction thermodynamics by affecting the stability of reactants and products. Different oxidation states can have varying enthalpies of formation and Gibbs free energies, impacting the overall energy changes and spontaneity of reactions.

50. Can you explain how variable valency relates to the concept of electron affinity?

While electron affinity typically refers to the energy change when a neutral atom gains an electron, variable valency is related to the ability of an atom to gain or lose multiple electrons. Elements with high electron affinities often exhibit variable valency in their anionic forms.

51. What is the significance of variable valency in nuclear chemistry?

In nuclear chemistry, variable valency affects the chemical behavior of radioactive isotopes and their decay products. Different oxidation states can influence the mobility and reactivity of radioactive elements in the environment and in nuclear fuel processing.

52. How does variable valency impact the formation of interstitial compounds?

Variable valency allows for the formation of various interstitial compounds, where atoms of one element occupy the spaces between atoms of another. Different oxidation states can lead to different sized ions, affecting which interstitial sites can be occupied.

53. How does variable valency affect the principles of hard and soft acids and bases (HSAB)?

Variable valency influences HSAB behavior. Different oxidation states of an element can exhibit varying degrees of hardness or softness, affecting their preferences for hard or soft ligands and their reactivity patterns in acid-base chemistry.

54. What is the role of variable valency in the chemistry of lanthanide contraction?

Lanthanide contraction, the decrease in atomic and ionic radii across the lanthanide series, is influenced by variable valency. The ability of lanthanides to exist in multiple oxidation states affects their ionic sizes and chemical behavior throughout the series.

55. How does variable valency impact the design and function of molecular machines?

In molecular machines, variable valency plays a crucial role in creating switchable or responsive components. The ability to change oxidation states can be used to induce conformational changes or alter binding affinities, enabling the design of molecular-scale devices that can perform mechanical tasks in response to chemical or electrochemical stimuli.