Chemical Bonding as the name suggests means the interaction of different elements or compounds which defines the properties of matter. Chemical bonds are formed when either at least one electron is lost to another atom, obtaining at least one electron from a different atom, or transferring one electron to another atom. In this article, we will learn about the theories of chemical bonding such as Lewis’s theory which explains the Lewis structure of any compound, Kossel’s Theory, and Fajan’s rule. So, let’s begin the journey of Chemical Bonding.
What is Chemical Bonding?
Chemical bonding is the formation of a chemical bond between two or more atoms, molecules, or ions that results in the formation of a chemical compound. These chemical bonds are what hold the atoms in the resulting compound together.
Chemical bonding is the attractive force that holds various constituents (atoms, ions, etc.) together and stabilizes them through the overall loss of energy. As a result, chemical compounds are dependent on the strength of the chemical bonds between their constituents; the stronger the bonding between the constituents, the more stable the resulting compound.
The inverse is also true: if the chemical bonding between the constituents is weak, the resulting compound will be unstable and will easily undergo another reaction to produce a more stable chemical compound (containing stronger bonds). Atoms try to lose energy in order to find stability. When one form of matter interacts with another, a force is exerted on the first. When the forces of nature are attractive, the energy decreases. When the forces of nature are repulsive, the energy increases. The chemical bond is the attractive force that holds two atoms together.
Theories on Chemical Bonding
There are two important theories on chemical bonding, and those are:
- Lewis’s Theory of Chemical Bonding
- Kossel’s Theory of Chemical Bonding
Let’s understand these theories in detail as follows:
Lewis Theory of Chemical Bonding
The Lewis theory of chemical bonding, also known as the Lewis electron dot theory, was proposed by the American chemist Gilbert N. Lewis in 1916. It provides a simple model to understand how atoms bond together to form molecules by focusing on the arrangement of valence electrons.
According to the Lewis theory, atoms gain, lose, or share electrons in order to achieve a stable electron configuration similar to that of noble gases. Noble gases have complete outer electron shells, making them highly stable and unreactive. Lewis recognized that other atoms tend to react in ways that allow them to acquire a similar electron configuration.
Key points of Lewis’s Theory of Chemical Bonding are as follows:
- An atom is made up of two parts: a positively charged Kernel (the nucleus plus the inner electrons) and an outer shell that contains electrons.
- The outmost shell can only hold a maximum of eight electrons.
- The outer shell’s eight electrons occupy the four corners of a cube that surrounds the ‘Kernel.’
- Atoms with an octet configuration, i.e., 8 electrons in the outermost shell, represent a stable configuration.
- In general, an element’s valency is equal to the number of dots in the corresponding Lewis symbol or 8 minus the number of dots (or valence electrons).
- Atoms with eight electrons in their outer shell are said to have a stable configuration. Atoms with fewer than eight electrons in their outer shell will try to gain electrons to achieve a stable configuration. Atoms with more than eight electrons in their outer shell will try to lose electrons to achieve a stable configuration.
- Chemical bonds are formed when atoms share, gain, or lose electrons to achieve a stable configuration.
- The number of dots in a Lewis symbol represents the number of valence electrons in an atom.
- The valency of an atom is the number of valence electrons that an atom can share, gain, or lose to achieve a stable configuration.
The key concept in the Lewis theory is the valence shell, which consists of the outermost energy level of an atom. Lewis represented valence electrons as dots around the atomic symbol. For example, the element oxygen (O) has six valence electrons, so it is represented as O with six dots around it.
Explanation of Bonds using Lewis Theory
The Lewis theory uses electron-dot symbols to depict the valence electrons of atoms and then suggests that atoms form bonds by sharing or transferring these electrons. The two main types of chemical bonds described by the Lewis theory are:
- Ionic Bonds: In ionic bonding, atoms transfer electrons to form ions with opposite charges. The transfer occurs from an atom with low ionization energy (tends to lose electrons) to an atom with high electron affinity (tends to gain electrons). The resulting oppositely charged ions are held together by electrostatic forces, creating an ionic compound. For example, sodium (Na) donates an electron to chlorine (Cl) to form sodium chloride (NaCl).
- Covalent Bonds: In covalent bonding, atoms share electrons to achieve a stable electron configuration. This type of bonding typically occurs between nonmetals. The shared electrons are represented by pairs of dots or lines between the atoms. For example, in a molecule of water (H2O), oxygen shares electrons with two hydrogen atoms.
Kossel’s Theory of Chemical Bonding
Kossel’s theory of chemical bonding, also known as the electron transfer theory, was proposed by the German physicist Walther Kossel in the early 20th century. Kossel noticed that the highly electronegative halogens and the highly electropositive alkali metals are separated by noble gases and his theory focuses on the transfer of electrons between atoms as the basis for chemical bonding, particularly in ionic compounds. Koss el’s theory builds upon the concept of the octet rule and the key points of Kessel’s Theory of Chemical Bonding are as follows:
- Electron Transfer: Kossel proposed that atoms form bonds by the complete transfer of electrons from one atom to another. This transfer occurs between an atom with low ionization energy (tends to lose electrons) and an atom with a high electron affinity (tends to gain electrons). The result is the formation of positively charged cations and negatively charged anions that are held together by electrostatic forces.
- Ionic Bonding: Kossel’s theory emphasizes ionic bonding as the primary type of bonding in many compounds. It suggests that when an atom loses or gains electrons to achieve a stable electron configuration, it becomes an ion. The positively charged cations and negatively charged anions then attract each other, forming an ionic bond. This bonding occurs between metals and nonmetals.
- Stability of Noble Gas Configuration: Kossel’s theory focuses on achieving a stable electron configuration similar to noble gases. By transferring or sharing electrons, atoms strive to attain a complete outer electron shell with eight valence electrons, except for hydrogen and helium, which can achieve stability with two valence electrons.
Fajan’s rule is postulated by Kazimierz Fajans in 1923. Fajans’ rule determines whether a chemical bond is covalent or ionic. He was able to predict ionic or covalent bonding at the time using X-ray crystallography and attributes such as ionic and atomic radius. The key points of Fajan’s rule are as follows:
- Polarizing Power: Fajan’s rule states that cations with a higher charge or smaller size have greater polarizing power. A cation with a higher charge density, resulting from a higher charge or smaller size, can pull the shared electrons in a bond closer to itself, creating a more polar bond.
- Polarizability: Fajan’s rule also considers the concept of polarizability, which refers to the ease with which the electron cloud of an atom or ion can be distorted. An anion with a larger size and more diffuse electron cloud is more easily polarized.
- Ionic Character: According to Fajan’s rule, a chemical bond between a cation and an anion with high polarizing power and high polarizability respectively exhibits a greater degree of ionic character. In other words, the electrons in the bond are more localized towards the cation, creating a polar covalent or even an ionic bond.
- Covalent Character: Conversely, a bond between species with low polarizing power and low polarizability tends to have a more covalent character. The electrons in the bond are more evenly shared between the atoms, resulting in a less polar or even nonpolar bond.
Examples of Fajan’s Rule
Some examples of Fajan’s Rule are as follows:
- Sodium chloride (NaCl) has a low polarizing power cation (Na+) and a small polarizability anion (Cl–). Therefore, NaCl has a high degree of ionic character.
- Magnesium oxide (MgO) has a high polarizing power cation (Mg2+) and a large polarizability anion (O2-). Therefore, MgO has a lower degree of ionic character and a higher degree of covalent character.
- Aluminum iodide (AlI3) has a very high polarizing power cation (Al3+) and a very large polarizability anion (I–). Therefore, AII3 has a very low degree of ionic character and a very high degree of covalent character.
Types of Chemical Bonds
The strength and properties of the chemical bonds formed vary. There are four primary types of chemical bonds that atoms or molecules form to form compounds. Chemical bonds of this type are-
- Ionic Bonds
- Covalent Bonds
- Hydrogen Bonds
- Polar Bonds
Ionic bonds are formed by the loss and gain of electrons. The atom which loses electrons is called a cation and is positively Charged while the atom which gains electrons is called an anion and is negatively charged. The Ionic bond is formed due to the electrostatic interaction between the cation and anion. Example – NaCl
Covalent bonds are formed by the sharing of electrons. These types of bonds are formed when the atoms are not loose or gain electrons and hence they share their electrons with each other. The electrons of each atom revolve in the atom’s orbit as well as other atoms’ orbit with which the bond is formed.
Hydrogen Bonds are formed between the H and F or O or N atoms of another molecule. This is an intermolecular bond. For Example, in water, within an H2O molecule, the hydrogens are attached to Oxygen with a covalent bond while the Hydrogen of the molecule bond with the O of another H2O molecule with a hydrogen bond.
Polar Bonds are a type of covalent bond formed between two atoms due to the unequal distribution of electrons in the bond. The more electronegative atom attracts the shared pair of electrons within itself forming a slightly negative charge on the electronegative element and partially positive on the other bonded atom.
For More Details Read, Types of Chemical Bonds
Sample Questions on Chemical Bonding
Question 1: Why do atoms react?
Atoms with eight electrons in their final orbit are stable and do not react. Atoms with fewer than eight electrons react with other atoms to gain eight electrons in their outermost orbit and thus become stable.
Question 2: How do atoms react?
Atoms in their final orbit with eight electrons are stable and do not react. Atoms with fewer than eight electrons react with other atoms, gaining eight electrons in their outermost orbit and becoming stable.
Question 3: What are the forces that keep reacting atoms together?
Because the outer orbitals of atoms overlap in metals, the electrons present in them do not belong to any specific atom, but rather flow over to all atoms and bind them all together (metallic bonding). Atoms that lose and gain electrons combine to form ions, which are held together by electrostatic forces of attraction (Ionic Bond). When atoms give and share electrons equally, the shared electrons serve as a unifying force between them (covalent bond).
Question 4: What are hybridized orbitals?
Relatively similar energy sub-orbitals can combine to generate a new set of the same number of orbitals, with all contributing orbitals having the feature of proportionality. They are called hybridized orbitals.
Question 5: Why is oxygen molecule paramagnetic?
The oxygen molecule is formed when an oxygen atom shares two electrons with another oxygen atom. The oxygen molecule is paramagnetic, indicating that it contains unpaired electrons. To explain this, a molecular orbital theory has been proposed. According to this theory, atoms lose their orbitals and instead form an equal number of orbitals that cover the entire molecule, giving rise to the term molecular orbital. The filling of these orbitals in increasing energy order results in unpaired electrons, which explains the paramagnetic behaviour of the oxygen molecule.
FAQs on Chemical Bonding
Q1: Define Chemical Bonding.
Chemical bonding refers to the attractive forces that hold atoms together in a molecule or compound. It involves the sharing, transfer, or redistribution of electrons between atoms to achieve a more stable electronic configuration.
Q2: What are the Different Types of Chemical Bonds?
Different types of chemicals bonds are:
- Ionic Bonds
- Covalent Bonds
- Hydrogen Bonds
- Polar Bonds
Q3: What is an Ionic Bond?
An ionic bond is a type of chemical bond formed between two atoms of significantly different electronegativities. One atom donates electrons (forming a cation) while the other accepts electrons (forming an anion), resulting in an electrostatic attraction between the oppositely charged ions.
Q4: What is a Covalent Bond?
A covalent bond is a chemical bond formed by the sharing of electron pairs between atoms. It typically occurs between nonmetal atoms that have similar electronegativities, allowing them to share electrons and achieve a more stable electron configuration.
Q5: What is Electronegativity?
Electronegativity is a measure of an atom’s ability to attract electrons towards itself in a chemical bond. It is based on the atom’s nuclear charge, distance from the valence electrons, and shielding effect of inner electrons. Electronegativity values help predict the type of bonding (ionic or covalent) that will occur between atoms.
Q6: How do you determine the Type of Bond formed between Two Atoms?
The type of bond formed between two atoms depends on the difference in their electronegativities. If the electronegativity difference is large (typically >1.7), an ionic bond is formed. If the electronegativity difference is small (typically <1.7), a covalent bond is formed. Intermediate values may indicate a polar covalent bond.
Q7: Can Atoms form Multiple Bonds?
Yes, atoms can form multiple bonds. For example, carbon can form four covalent bonds by sharing multiple electron pairs, as seen in molecules like methane (CH4) and ethene (C2H4).
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