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Last updated date: 16th May 2024
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Definition of valency

Valency is the number of atoms of a particular element that is combined with one atom of another element to form a molecule. Valency is also known as molecular weight. Valency is a measure of the combining power of an atom. The valency of an element is determined by the number of electrons in its outermost shell. The valency of an element can be increased either by gaining or losing electrons.

The Valence, or known as valency, in Chemistry, is the characteristics of an element that indicates the number of other atoms with which an atom of a particular element can form a covalent bond. Introduced in 1868, the term is used for the expression of both the possibility of combination of an element in general and the numerical value of the power of combination. Thus valence meaning is the number of electrons as most of the bonds are formed by the exchange of the valence electrons. The valence electrons determine the valency meaning in Chemistry and define what is valences in Chemistry.

Importance of Valency

The valency of an element is important because it determines how strong the bond between the atoms will be. The higher the valency, the stronger the bond. This is why elements with a high valency are often used in chemical reactions - they form strong bonds with other atoms.

Valency is also an important concept in chemistry because it helps us understand how atoms join together to form molecules. By understanding valency, we can better predict how chemicals will react with each other. This makes it easier to create new compounds for use in various industries. Valency is a fundamental concept that helps us understand the world around us.

Valency is an important measure of the combining power of atoms. The valency of an atom is determined by the number of electrons in its outermost shell. The valency of an element can be increased either by gaining or losing electrons. Valency is important because it gives us information about how atoms combine and why certain chemicals react the way they do. Valency also helps us predict the properties of new compounds that we create. Valence is fundamental to chemistry!

A Brief Account of Valence Chemistry

The explanation and the systematization of the concept of valence or valency was one of the major challenges for 19th-century chemists. As there was no satisfactory theory for the cause of valency, most of the efforts were done on making empirical rules for the determination of the valencies of the elements. The characteristic valence of elements was measured in terms of the number of atoms of hydrogen with which an atom of the element can merge or that it can replace in a compound. It later was quite evident, however, that the valencies of many of the elements varied in different compounds. 


The first great step in the development of a satisfactory explanation of valence and chemical combination was made by the American chemist G. N. Lewis in 1916 with the identification of the chemical bond present in the organic compounds as a pair of electrons was held jointly by two atoms which were holding them together. In the same year, the nature of the chemical bond between electrically charged atoms, or also known as ions, was discussed by the German physicist W. Kossel. 


The valence theory was reformulated and described incorporating electronic structures and interatomic forces after significant development in the field of electronic theory of periodicity of elements. Due to this several new concepts were introduced which included ionic valence, covalence, oxidation number, coordination number and metallic valence which also explain the different modes of atomic interactions. 

Define Valence and Valency

Most of the definitions in Chemistry are defined by IUPAC. Hence, the definitions in valence chemistry are also given by IUPAC. As per the IUPAC valence meaning is defined as the maximum number of single valence atoms that can possibly merge with an atom of the particular element under study, or with a fragment, or for which an atom of this element can be substituted.


Another description used to define valence in modern times is - The number of possible hydrogen atoms that can merge with an element in a binary hydride or twice the number of oxygen atoms that combine with an element in its oxide or oxides forms. This definition differs from the IUPAC definition as an element can be said to have more than one valence possible.


Another modern valence definition stating the valence meaning is that the valence of a particular atom present in a molecule is the number of electrons that an atom uses in the formation of a bond. This is represented by the formulas for calculating the valence electrons that can also be used to define valence is:


Valence = number of electrons in the last/valence shell of a free atom - Number of electrons on an atom in molecules that are not bonded. Hence, valency definition in chemistry can be shown by the formula as


Valence or Valency = Number of bonds formed + Formal charge of the atom.

The Valency and Number of Electrons

The Rutherford Model of the nucleus of an atom shows that the outside of an atom is filled by electrons, suggesting that the electrons are the ones responsible for the interaction of the atoms and the formation of the chemical bonds. Later, G. N. Lewis explained the valence and chemical bonding in terms of the nature of atoms to acquire a stable octet of eight valence-shell electrons. According to the theory proposed by Lewis, covalent bond formation leads to octet structure by sharing of the electrons, while ionic bonding leads to octet structure by the transfer of electrons from one atom to the other. 


Another term related to valence is covalence, which is the number of electron pairs shared by one atom with another atom. Also, by name co- means together, indicating that a covalent bond is that bond in which the atoms share a valence. Hence, it is now more common to say covalent bonds rather than using valence and valence meaning in Chemistry in high-level work done in advancing the theory of chemical bonding although it is widely used in the understanding of the basic concepts which provide an introduction to the topic.


Linus Pauling, during the 1930s, proposed the existence of polar covalent bonds which are possible intermediaries in between the covalent and the ionic bond. He also stated that the degree of the ionic character in such a bond was influenced by the electronegativity of the two atoms participating in a bond formation. He also considered the hypervalent molecules. These molecules are the ones in which the main group of elements have valences greater than the maximum of 4 allowed valences by the octet rule. 


An example of this case is the sulphur hexafluoride molecule (SF6), where according to Pauling the sulfur forms six two-electron bonds using sp3d2 hybridization of the atomic orbitals, merging one s, three p and two d orbitals. But the recent quantum mechanical calculations on this and similar types of molecules show that the role of the d-orbitals in such bonding is minimal and the SF6 molecule has to be described as having six polar covalent bonds, which are also partly ionic, made from only four of the orbitals on sulfur which is one s and three p following the octet rule, along with six orbitals on the fluorines. Similar calculations on transition-metal molecules also show that the role of p orbitals is minor, and hence one s and five d orbitals on the metal are sufficient enough to describe the bonding.

Here are Some Examples of Valencies:

The valencies of some common elements are as follows:

  • Carbon: 4

  • Oxygen: 2

  • Hydrogen: 1

  • Nitrogen: 3

  • Sodium: 1

  • Chlorine: 1

  • Potassium: 1

  • Magnesium: 2

  • Calcium: 2

  • Iron: 2 or 3 (depending on the oxidation state)

Valency is Applied in Various Areas:

1) In Medicine: valency is used to determine the efficacy of a drug. Valency predicts how much drug will be needed in order to treat a patient. Valency also determines how easily a drug can cross biological membranes such as the placenta (for pregnant women), blood-brain barrier (for patients with neurodegenerative diseases like Alzheimer's or Parkinson's), and intestinal wall (for patients who need treatment for infections).

2) In Genetics: valency results from the binding of two alleles at a single loci, where each allele may have a different valence depending on its own gene product and that of another allele present at the same locus.

3) In Environmental Sciences: valency indicates the degree to which chemicals will interact with each other and the potential for chemical reaction.

4) In Industrial Chemistry: valency is used to predict the properties of compounds and their suitability for particular applications.

5) In Predicting the Properties of the Compound- valency helps in predicting the physical and chemical properties of the valency.

6) In Synthetic Organic Chemistry: valency is used to plan the construction of molecular structures.

7) In Studying the Structure of Inorganic Materials: valency provides a simple way of classifying complex inorganic materials.

8) In Studying the Bonding in Metals: valency is used to understand why some alloys have better mechanical properties than others.

9) In Solid-State Physics: valency is used to classify solids on the basis of their bonding arrangements.

10) Valency has wide applicability across many scientific disciplines. By understanding valency, we can better predict how chemicals will react with each other and create new compounds for various applications. Valency is a fundamental concept in chemistry.

Here are Some Tips to Study Valency:

1) Know the Basics- It is important to know the valencies of the common elements. This will give you a basic understanding of valency.

2) Practice Identifying Valencies- Try to identify the valency of different elements. This will help you better understand how valency works.

3) Use Valency to Predict Chemical Reactions- By understanding valency, you can better predict how chemicals will react with each other. This can help you create new compounds for various applications.

4) Review Key Concepts Regularly- valency is a complex concept, and it is important to review key concepts regularly. This will help you better understand valency and its applications.

5) Ask Questions- If you don't understand something, ask your teacher or classmates for help. Nobody knows everything and collaboration can be very effective in valency.

6) Avoid Cramming- while studying valency one should avoid cramming. This will only lead to confusion and frustration. Valency should be studied gradually, and one should allow enough time to fully understand the concept.

FAQs on Valency

1. What are valency and example?

Valency is the number of unpaired electrons that is present in the outside shell of the atomic orbits. The last unpaired in an electronic configuration is known as the valency of that element. For example, the atomic number of sodium is 11 and the number of last unpaired electrons contributes to the valency with the unpaired electron being 1. Hence, the valency of sodium is 1.

2. Can valency be negative?

With the loss and gain of an electron, there is again and loss of charge on the atom. The loss and gain of the charge can be of positive or negative representation but not valency. The Valency simply states the valence electron or the last unpaired electron in an atomic orbit.

3. What is valency? How does valency help organize atoms into molecules?

Valency refers to the combining power of an atom in regard to making a chemical bond with another atom or with itself. Valency organizes atoms into molecules that have different physical and chemical properties, such as solubility and density. Valency also determines how easily a molecule can diffuse across biological membranes and how it will react with other chemicals. Understanding valency can help scientists predict how certain molecules will behave and assist them in synthesizing new compounds for various applications.

4. What are some examples of valencies we encounter every day?

Some common examples of Valency include ionic bonds, covalent bonds, hydrogen bonds valency is used to understand how molecules interact with each other. valence is also important in understanding the structure of polymers, where valency helps determine the solubility of a polymer in different solvents.

5. What are some valency concepts?

Some common valency concepts include ionic bonding, covalent bonding, hydrogen bonding, and valency states. Valency states describe elements that have more than one valence. Ionic bonds form when metal atoms lose valence electrons to become positively charged ions while non-metal atoms gain these valence electrons to become negatively charged ions. Covalent bonds form between two nonmetals through sharing electron pairs between them. Hydrogen bonds form between hydrogen and another electronegative atom such as oxygen or nitrogen. valency states describe elements that have more than one valence, such as chromium which can exist in valency states of +2 and +3. Valency is a fundamental concept in chemistry and it has numerous applications across scientific disciplines.

6. What can valency be used to explain? How does valency help us understand chemical reactions?

Valency can be used to explain the behaviour of molecules, large biological structures like proteins, and even the arrangement of elements in solids. Valency is an important factor in understanding chemical reactions. In many cases, it is the only variable that scientists can control when trying to predict how a reaction will occur. By understanding valency, scientists can better understand how molecules interact with each other and what kind of reactions are possible. Valency is also essential in creating new compounds for various applications.

7. What should I do if I don't understand something about valency?

If you don't understand something about Valency, ask your teacher or classmates for help. Nobody knows everything and collaboration can be very effective in Valancy. You may also want to review key concepts regularly until you have a better understanding of Valency's role in chemistry. Finally, avoid cramming- Valency should be studied gradually, and one should allow enough time to fully understand Valency.

8. How much time does it take to prepare for exams?

Valency is not an easy topic to learn, but practising Valency regularly can help students better understand Valency. It takes time and dedication in order to master Valency concepts that are essential for chemistry exams.

9. What final tips do you have about Valency?

First of all, study the basics of Valence thoroughly before moving on to more difficult topics like coordinate covalent bonds or electron pair repulsion theory. Second, make sure you take good notes when studying Valency- a review will be very beneficial in exam preparation! Finally, don't forget about your teacher's office hours - they were there during this entire course and want nothing more than for their students' success. They would love to answer any Valency questions you might have!