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Chemical Bond is known as the attractive force which can hold various constituents such as atoms and ions together in different chemical species. Molecular Structure is the arrangement of the atoms in the molecule and the types of bonds present or used to link these atoms. Chemical Bonding and Molecular Structure Class 11 Important Questions cover the description of bond strength and its relationship with bond order. Also, there is a description of valence bond theory, sigma bond, hybridization and other properties and structure of covalent bond. There is a complete explanation of Lewis Structure for H2S. Also, there is a differentiation between MOT and VBT.
Lewis Dot Structure
Read Also: Comparison Topics in Chemistry
Very Short Answer Type Questions (1 Mark Questions)
Ques: Define chemical bonding.
Ans: The chemical constituent of a chemical compound such as atom ions etc. bind together with the help of an attraction force is called chemical bonding.
Ques: Define hybridization. Also, mention hybridization for ammonium ion & NO2+.
Ans: Hybridization is defined as the mixing of two orbitals to form a new hybridised orbital having completely different shapes & energies.
NH4+= sp3
NO2+= sp
Ques: Give reason: The H—-N—-H bond angle is greater than the bond angle of H—-O—-H, even though both the central atoms nitrogen and oxygen have sp3 hybridization.
Ans: The H—-N—-H bond angle is greater than the bond angle of H—-O—-H, even though both the central atoms nitrogen and oxygen have sp³ hybridization. Because H2O has two lone pairs and has more repulsion than NH2 having one lone pair.
Ques: Give the reason why all the bonds between sulfur and oxygen in a sulphate ion have equal bond length.
Ans: The reason why all the bonds between sulfur and oxygen in a sulphate ion have equal bond length is Resonance which is the method for describing bonding in different types of molecules and ions.
Ques: For breaking a water molecule, the energy requirement for both the O–H bonds are different. Explain why?
Ans: This is due to the fact that the electronic charges around the oxygen atom remain changed after breaking one O–H bond.
Ques: Define ionic bonding?
Ans: It is formed when one atom donates electrons to another atom in order to stabilise itself.
Short Answer Type Questions (2 Marks Questions)
Ques: Describe Bond strength and also explain its relationship with bond order?
Ans: Bond strength is the extent to which two atoms hold each other while forming a chemical bond. Bond order on the other hand is the total number of chemical bonds present between the two atoms. Bond strength and bond order both are directly proportional to each other, i.e., with an increase in bond order, the bond strength also increases.
Ques: Give a reason – The shape of PCl5 is trigonal bipyramidal whereas the shape of IF5 is square pyramidal.
Ans: The shape of PCl5 or phosphorus pentachloride is trigonal bipyramidal because the central atom phosphorus is linked with five chlorine atoms, i.e., having 5 bond pairs and no lone pair on the other hand IF5 has one lone pair in addition to five bond pairs giving it the shape of square pyramidal.
Ques: Draw and explain the structure of Phosphorus chloride?
Ans: PCl3 contains three chlorine atoms linked to the central atom phosphorus through a sigma bond. It has a trigonal planar structure in which the p orbitals of chlorine overlap with the sp3 orbitals of phosphorus. Each chlorine atom carries three lone pairs of electrons.
Ques: Describe the octet rule?
Ans: According to this rule, In order to achieve the electronic configuration of the outer shell of any atom nearest to noble gas, the atoms either gain or lose their electrons from their outer shell.
Ques: Describe the Lewis dot structure with the help of one example?
Ans: Lewis dot structure is basically representing the arrangement of atoms in the molecule along with the kinds of bonds and lone pairs of electrons present in it. The diagram given below represents the structure of a water molecule, it also shows that all the atoms are connected via a sigma bond, and oxygen atoms have two lone pairs in them.
Long Answer Questions (3 Marks Questions)
Ques: Explain the structure of phosphorus trichloride and hydrogen sulphide with the help of diagrams.
Ans: Hydrogen sulphide (H2S) - If we take a look at the structure of hydrogen sulphide we observe that it looks similar to water. It has one sulfur atom which is also the central atom and is attached to two solitary hydrogen atoms. The total number of lone pairs present around sulfur atoms is 2, which is why there are a lot of repulsions that displace or move the H—S bond away, further giving it a non-planar structure.
Ques: Distinguish between the two concepts of electronegativity and electron affinity?
Ans: Following are the differences between electronegativity and electron affinity:
| Electronegativity | Electron affinity |
|---|---|
| Electronegativity is the capacity of an atom to attract electrons from outside in a covalent bond. | Electron affinity is the measurement of the amount of energy exerted on a neutral atom or molecule, the moment in which it converts to its ionic form. |
| It is a qualitative property. | It is quantitative in nature hence, its value can be easily determined or measured. |
| The Pauling scale is used to measure electronegativity. | Ev or kJ/mol units are used. |
| Example- In the molecule Cl—F, fluorine is more electronegative than chlorine atom. | Example- Approximately- 349KJ/mol energy is released when Cl atom ionises to form Cl-. |
Ques: Differentiate between an ionic bond and covalent bonding?
Ans: Following are the differences between an ionic bond and covalent bonding:
| Ionic bond | Covalent bond |
|---|---|
| It is formed when one atom donates electrons to another atom in order to stabilise itself. | It is formed when electrons are shared equally between two atoms. |
| The nature of the bond is polar. | The nature of the bond so formed is non-polar. |
| The molecules are able to conduct electricity. | Covalent compounds are electrically neutral. |
| Electronic orbitals do not overlap in the formation of ionic bonds. | Overlapping of orbitals occurs when covalent bonds are formed. |
Very Long Answer Questions (5 Marks Questions)
Ques: Write a short note on dipole moment?
Ans: Dipole moment occurs when there is a separation of charges between two atoms or ions in a covalent bond or ionic bond respectively or when the electrons are shared unequally or when there are differences in electronegativities of two-atom forming a bond together; dipole moments emerge from differences in electronegativity. The distance between the charges is additionally a main consideration for the size of the dipole moment and is capable of measuring the polarity of the molecule.
Formula For dipole moment: It is used to measure the distance between two separated charges by using debye units (1 debye= 3.335 x 1030 C-m or 10-18 esu cm) and is a vector quantity. It is basically determined when two electrical charges of the same magnitude but opposite signs are separated by a distance r due to which dipole moment is established. The dipole moment of homonuclear diatomic species such as oxygen, nitrogen is zero because of both the atoms having symmetrical charge distribution and the same electronegativity and ionisation energies, in contrast with heteronuclear diatomic species such as hydrogen chloride having non zero dipole moment value because of differences in electronegativity and ionisation energies value and asymmetrical charge distribution.
μ = q*r
- μ = Dipole moment
- q = charge
- r = distance between the centre of two charged particles
Significance of dipole moment: It can be used to determine various parameters such as:
- Bond angle
- Polarisation
- Percentage of ionic character
- Residual charges
- Arrangements of chemical bonds in a molecule
- Size & shape of the molecule
Ques: Compare \(\sigma\) and \(\Pi\) bond.
Ans: Comparisons are as follows:
| \(\sigma\) /sigma bond | \(\Pi\)/ pi bond |
|---|---|
| These types of bonds are comparatively stronger in nature. | These types of bonds are comparatively weaker in nature. |
| For the formation of sigma bonds, orbitals overlap from end to end also known as axial overlapping. | Lateral overlapping occurs in the case of the formation of the pi bond. |
| Restriction of rotation around the sigma bond is not present. | Restriction of rotation around the pi bond is present. |
| s–p, p–p, s–s are the types of orbitals participating in overlapping. | The orbital participating in overlapping is only p—p. |
| One symmetrical electron cloud is present. | Two Asymmetrical electron clouds are present both above & below the plane of the atomic line. |
| The framework of sigma bonds decides the overall shape of the molecule. | Pi bonds generally do not contribute to the shape of the molecule, instead it adds to the dimensions of the molecules. |
| It can be present alone or can be additionally present along with the pi bond. | Pi bonds can never exist alone, they are always superimposed over sigma bonds. |
Ques: In what ways valence bond theory is different from molecular orbital theory and VSEPR theory?
Ans:
- VBT vs VSEPR
| Valence bond theory/VBT | Valence shell electron repulsion theory(VSEPR) |
|---|---|
| It deals with the chemical bonds present between atoms. | It deals with the shape & geometry of a molecule. |
| The theory is based on the overlapping of orbitals in order to form chemical bonds. | The theory is based on the repulsion of the electrons of bond pairs & lone pairs. |
| Does not provide any idea about the shape of the molecule. | Indicates and provides idea about the shape and geometry of the molecule. |
| Contributes to the creation of bonds. | Does not contribute to the creation of a bond. |
| Given by the scientist Linus Pauling | Given by the scientist Ronald Gillespie and Ronald Nyholm |
- VBT vs MOT
| Valence bond theory/VBT | Molecular orbital theory/MOT |
|---|---|
| It is a theory that explains the formation of chemical bonds through the overlapping of hybrid orbitals. | It is the type of theory that deals with the formation of chemical bonds through overlapping molecular orbitals. |
| It uses the concept of overlapping hypothetical hybrid orbitals which means mixing atomic orbitals present in the same atom for the formation of the chemical bond. | It uses the concept of overlapping hypothetical molecular orbits which means mixing atomic orbitals present in different atoms in order to form covalent bonds. |
| Explains concepts like hybridization. | Explains concepts like bonding and antibonding molecular orbitals. |
| Given by the scientist Linus Pauling | Given by the scientists F.Hund & R.S Mulliken |
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