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Chemical bonding and Molecular Structure help study about groups of atoms that share similar species and characteristics. The bond that holds different constituents(atoms and particles) together in various synthetic species is known as a compound bond.
- Chemical bonding and Molecular Structure are included in NCERT Class 11 Chemistry.
- G N Lewis first presented this phenom with the assistance of electron pairs between molecules.
- He presented Lewis's dot structure, which depicts the compound holding between particles in an atom.
- Chemical bonding is the formation of chemical bonds between various atoms or molecules.
- VSEPR, valence bond theory, and molecular orbital theory help explain the formation of a bond.
- Ionic, Covalent and Polar bonds are types of chemical bonding.
- Chemical bonding and Molecular Structure can be found in our everyday lives.
- A real-life example is bonding between starch, sugar and proteins in our diet.
Key Terms: Chemical bonding and Molecular Structure, Chemical Bonding, Molecular Structure, Atoms, Octet rule, Electrons, Valence Electrons, Valence Shell, Covalent Bond, Ionic Bond, Lewis Theory, Hydrogen Bonds
What is Chemical Bonding?
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Chemical Bonding refers to the process of transforming different elements or substances under different sets of conditions. It explains the bond between atoms or molecules.
- The bond is formed by the electrostatic force between oppositely charged ions.
- It is also formed by the sharing of electrons by covalent bonds.
- Chemical bonds hold the atoms within molecules and crystals.
- Bonds between atoms can also be explained by quantum theory.
- The loss of energy takes place in the formation of chemical bonding.
- The stronger the bonding between the atoms, the more reliable the compounds will be.
Example of What is Chemical Bonding?Example: Chemical Bond is formed in the fuel or gases that are used in vehicles and cars. It is formed by bonds between atoms. |
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Important Theory on Chemical Bonding
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Some important theory on chemical bonding are as follows:
Kossel Lewis Hypothesis
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As per Lewis' methodology, the particles of various components take part in the synthetic blend to finish the octet (eight electrons in the peripheral valence shell) or duplet (two valence electrons at times, for example, H, Li, Be, and so on).
- Kossel Lewis's Hypothesis is known as the Octet Rule.
- At the point of development of an atom, the external shell electrons participate in the compound, which are known as valence electrons.
- All negatively charged ions and positively charged ions have a noble gas configuration.
- The atoms are held by electrostatic force.
Limitations of the Octet Rule
The limitations of the octet rule are as follows:
- The rule failed to predict the shape and relative stability of molecules.
- It is based on the inert nature of noble gases.
- However, some noble gases like xenon and krypton form compounds such as XeF2, KrF2, etc.
- The octet rule cannot be applied to the elements in and beyond the third period of the periodic table.
- The elements present in these periods have more than eight valence electrons around the central atom.
- The octet rule is not satisfied for all atoms in a molecule having an odd number of electrons.
- The rule cannot be applied to those compounds in which the number of electrons surrounding the central atom is less than eight.
Example of Limitations pf Octet RuleExample 1: PF5, SF6, etc. states that elements have more than eight valence electron. Example 2: NO and NO2 do not satisfy the octet rule as they have odd number of electrons. Example 3: LiCl, BeH2, AlCl3, etc. do not obey the octet rule when number of electron surrounding the central atom is less than eight. |
Lewis Theory
In Lewis theory, the base is responsible for donating electrons, and acid is responsible for sharing electrons. It means Lewis acid is known as an electron-pair acceptor, and Lewis base is known as an electron-pair pair-donor.
- The completion of oxidation and reduction reactions is an advantage of Lewis's theory.
- It also suggested that the oxidation number is kept constant when an acid reacts with a base.
- The theory is used for the expansion of acids.
- This means H+ ion acts as a Lewis acid and H2O acts as a Lewis base.
- The product formed when acid reacts with base is called Lewis adduct.
Types of Chemical Bonding
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There are four types of chemical bonding which are as follows:
Ionic Bond
An Ionic or electrovalent bond is framed by the total exchange of electrons starting with one atom then onto the next. It is framed among metals and non-metals.
- It is the electrostatic power of fascination which holds the oppositely charged particles together.
The development of ionic mixtures would basically rely on:
- The simplicity of arrangement of the positive and negative particles.
- The plan of the positive and negative particles in the cross-section of the glasslike compound.
M(g) → M+ (g) + e–Ionization enthalpy
X(g) + e–→ X – (g) Electron acquire enthalpy
Covalent Bond
Covalent Bond is a type of bond that involves sharing of atoms. Organic compounds having carbon atoms tends to exhibit this type of chemical bonding.It kead to the creation of molecule.
Polar Bond
Polar bonds is a type of bond that result in the formation of molecules that are polar or non-polar in nature. In this electrons are shared unequally as more electronegative atom pulls the electron pair closer to itself and away from the less electronegative atom.
Hydrogen Bond
Hydrogen Bonding is a type of weaker covalent bond between oxygen and hydrogen atoms. In this hydrogen atom carries a partial positive charge on the atom.
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Bond Characteristics
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The important bond characteristics are as follows:
Bond Length
Bond length is an equilibrium distance between the centres of the nuclei of the two bonded atoms. It is expressed in terms of A.
Bond Angle
Bond Angle is characterized as the point between the orbitals consisting of holding electron sets around the focal iota in an atom/complex particle. Bond points are communicated in degrees which are tentatively controlled by spectroscopic strategies.
Bond Enthalpy
Bond Enthalpy is the measure of energy needed to break one mole of obligations of a specific sort between two molecules in a vaporous state. The unit of bond enthalpy is kJ mol–1.
- The more the Bond Enthalpy, the more grounded the bond is.
Example of Bond EnthalpyExample: Hydrogen's H—H bond enthalpy is 435.8 kJ mol-1 |
Bond Order
According to Lewis, Bond Order is given by the number of connections between the two atoms in a particle.
Example of Bond OrderExample 1: Bond order of H2 (H —H) =1 Example 2: Bond order of O2 (O = O) =2 Example 3: Bond order of N2 (N = N) =3 |
Resonance Structure
In the resonance structure, it is observed that there are many molecules whose behaviour cannot be explained by a single Lewis structure.
Example of Resonance StructureExample: Lewis's structure of Ozone is represented as follows: In the two designs, we have an O–O single bond and an O=O twofold bond. The typical O–O and O=O bond lengths are 148 pm and 121 pm individually. Not really set in stone oxygen-oxygen bond lengths in the O3 atom are the same (128 pm).
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Lattice Enthalpy
The Lattice Enthalpy of an ionic solid is defined as the energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions.
It depends upon the following variable
- Size of the particles: Smaller the size, the more prominent will be the cross section energy.
- Charge on the particles: Greater the size of the charge, more noteworthy the interionic fascination, and thus higher the cross-section energy.
Dipole Moment
In this, polar atoms are called dipole particles and they have a dipole second. Dipole second is characterized as the result of the size of the positive or negative charge and the distance between the charges.
Geometry of Molecules
The geometry of molecules can be explained with the below image:
Valence Bond Theory
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Valence Bond Theory depends on the idea of nuclear orbitals and the electronic arrangement of the particles. Let’s consider the development of hydrogen atoms dependent on the valence bond hypothesis.
- Two hydrogen molecules, A and B, have their cores NA and NB.
- Electrons present in them are eA and eB.
- As these two atoms come nearer, new appealing and loathsome powers start to work.
- The nucleus of one atom is attracted towards its electron and the electron of the other and vice versa.
- Repulsive forces arise between the electrons of two atoms and nuclei of two atoms.
- Attractive forces tend to bring the two atoms closer, whereas repulsive forces tend to push them apart.
Orbit Overlap
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In Orbital Overlap Connect, the arrangement of hydrogen particles, there is a base energy state when two hydrogen atoms are close to the point that their nuclear orbitals go through halfway interpenetration.
- This incomplete convergence of nuclear orbitals is called covering of nuclear orbitals.
- The degree of cross-over chooses the strength of a covalent bond.
Types of Orbital Overlap
Contingent on the sort of covering, the covalent bonds are of two kinds, known as Sigma and Pi Bonds
Sigma (σ bond)
Sigma bond is shaped by the start to finish (head-on) cross-over of holding orbitals along the internuclear pivot.
Pi Bond
Pi bond is lateral overlapping of two lobes of one atomic orbital with lobes of another overlapping orbitals. The pivotal cross-over including these orbitals is of three kinds
- s-s covering
- s-p covering
- p-p covering
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Hybridisation
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Hybridisation is the process of intermixing the orbitals of slightly different energies. It redistribute their energies resulting in the formation of new sets of orbitals of equivalent energies and shapes.
- Hybridization involves mixing of atomic orbitals of comparable energies.
- It involves merging of two s’ or two p’orbitals.
- In some cases, merging of s orbital with p orbital or s with d orbital take place.
- The new orbitals formed by the process of hybridisation are hybrid orbitals.
Types of Hybridisation
The different types of hybridisation are as follows:
sp
In this one s orbital mix with one p orbital to form two new equivalent orbitals.
sp2
In this one s orbital mix with two p orbital to form three new equivalent orbitals.
sp3
In this one s orbital mix with three p orbital to form four new equivalent orbitals.
sp3d
In this one s orbital mix with three p orbital and one d orbital to form five new equivalent orbitals.
sp3d2
In this one s orbital mix with three p orbital and two d orbital to form six new equivalent orbitals.
Important Topics for JEE MainAs per JEE Main 2024 Session 1, some important topics included in the chapter Chemical Bonding and Molecular Structure are as follows:
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Things to Remember
- Chemical bonding and Molecular Structure involves attraction between atoms, ions, or molecules.
- The electrostatic force of attraction between oppositely charged ions are formed between molecules.
- sp, sp2, sp3, sp3d and sp3d2 are different types of hybridisation.
- Bond angle, length and enthalpy are important bond cahracteristics.
- Students can practice NCERT Solutions for Class 11 Chemistry Chapter 4: Chemical Bonding and Molecular Structure.
- The chapter is provided with Important MCQs on Chemical Bonding and Molecular Structure.
Previous Years Questions
- Among the following species, identify the pair having same bond order
- The types of hybridisation on the five carbon atoms from left to right in the molecule
- Which of the following bonds require the largest amount of bond energy to dissociate the atoms concerned ?
- Which one of the following has the smallest bond angle ?
- An odd electron molecule among the following is
- Arrange the following species in the correct order of their stability
- In which of the following molecules the central atom does not follow the octet rule ?
- Which of the following pair have identical bond order?
- Identify the T-shaped molecule in the following
- The paramagnetism of O+2 is due to the presence of an odd electron in the MO
Sample Questions
Ques. How can one nonpolar molecule induce a dipole in a nearby non-polar molecule? (2 marks)
Ans.Instantaneous dipoles results in the creation of specific positions of electrons in nonpolar molecules. This instantaneous dipole can induce a dipole in nearby non polar molecules. Polar atoms are called dipole particles and they have a dipole second.
Ques. What are some differences between an ionic bond and a covalent bond? (4 marks)
Ans. The differences between an ionic and covalent bond are as follows:
| Ionic bonds | Covalent bonds |
|---|---|
| Ionic bonds are formed by electrostatic forces between two oppositely charged atoms. | Covalent bonds are formed by sharing of electrons between two atoms. |
| In solution, ionic molecules will dissociate into their respective ions. | In solution, covalent molecules do not dissociate as such. They may retain their molecularity. |
| Metals mostly form ionic bonds. | Non-metals mostly form covalent bonds. |
| Ex- kcl, beo, agbr | Ex- o2, co2, cl2 |
Ques. What are pi bonds and how are they formed? (2 marks)
Ans. Pi bonds are chemical bonds that are covalent and involve the lateral overlapping of two lobes of an atomic orbital with two lobes of another atomic orbital that belongs to a different atom. Pi bonds are formed from the overlap of parallel p orbitals on adjacent atoms.
Ques. Why is the energy absorbed when bonds are broken? (3 marks)
Ans. During chemical reactions, bonds in reactants break, and new bonds are formed on the product side. When a bond is broken energy is absorbed as it is an endothermic process and energy is released while bond making is an exothermic process so the reaction is endothermic or exothermic depending on the difference between the energy needed to break bonds and the energy released when new bonds form.
Ques. What is the difference between valency and covalency? (3 marks)
Ans. The difference between valency and covalency are as follows:
| Valency | Covalency |
|---|---|
| Valency is the process where number of electron an atom gain or lose to become completely stabilised. | Covalency is the process where the number of bond an atom shares with empty orbitals. |
| It is responsible for forming both ionic and covalent bond. | It is responsible for forming covalent bond. |
| Valency does not depend upon the number of valence electrons. | Covalency depends upon the number of valence electrons. |
Ques. What are the factors that affect the bond angles? (3 marks)
Ans. The factors that affect the bond angles are as follows:
- The angle is proportional to the electronegativity of the central atom.
- Bong angle is inversely proportional to the electronegativity of the peripheral atoms and percentage of p character of the hybridised orbitals.
- It is proportional to the size of peripheral atoms of the molecule.
- The required angle is proportional to the percentage of s character of the orbitals.
- It is inversely proportional to the percentage of p character of the orbitals.
Ques. Explain Fagan’s Rule? (3 marks)
Ans. Fagan’s Rule is a type of rule that involves covalent bond formed possess some partial ionic character whereas the ionic bondsformed possess partial covalent character.
- The partial covalent and ionic character is measured with the help of fagan’s rule.
- It depend upon the size of cation and anion.
- In this size of cation is smaller and size of anion is larger.
- Cations having greatee charge will exhibit more stronger ionic bond.
- Transition metal cations are more polarised in nature that noble gas cation.
Ques. What are the factors affecting bond enthalpy? (2 marks)
Ans. The factors affecting the bond enthalpy are as follows:
- Size of the atom
- Multiplicity of bond
- Bond angle
- Bond order
- Number of lone pair of electron
Ques. What is the difference between covalent and hydrogen bond? (4 marks)
Ans. The difference between covalent and hydrogen bond are as follows:
| Covalent Bond | Hydrogen Bond |
|---|---|
| Covalent bond is formed by sharing of electrons. | Hydrogen Bonding is a type of weaker covalent bond between oxygen and hydrogen atoms. |
| It forms interatomic bonds.. | It forms intramolecular or intermolecular bonds. |
| The bond strength is 100-110 KJ/mol | The bond strength is 5-50 KJ/mol |
| It is formed in lesser electronegativity difference atom. | It is formed in more electronegativity difference atom. |
Ques. Explain molecular orbital theory? (3 marks)
Ans. Molecular Orbital Theory stands for MOT which involves chemical bonding of atoms. The theory was proposed by F. Hund and R. S. Mulliken in the twentieth century.
- It describe the structure and properties of different molecules..
- The theory is more powerful in comparison to the valence-bond theory.
- In this molecular orbitals formed will always be equal to the total number of atomic orbitals.
- The elctrons are filled by increasing order of orbital energy.
- Bonding molecular orbitals, anti-bonding molecular orbitals and non-bonding molecular orbitals are three different types of MOT.
Ques. What is London dispersion forces? (2 marks)
Ans. London disperison forces are forces that are formed by the temporary imbalances of charge occurring inside an atom. In this charge of atom are under constant changes as these electrons are always in motion. It is the weakest intermolecular force. In this electrons in two adjacent atoms are displaced in such a way that it get some temporary dipoles.
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