Chemical Bonding and Molecular Structure MCQ Quiz - Objective Question with Answer for Chemical Bonding and Molecular Structure - Download Free PDF

CONCEPT:

Bond Angle

• The bond angle is determined by the repulsion between bonding pairs and lone pairs of electrons around the central atom, as described by the VSEPR (Valence Shell Electron Pair Repulsion) theory.
• The presence of lone pairs reduces bond angles as they exert greater repulsion compared to bonding pairs.
• Bond angles are largest in symmetrical molecules with only bonding pairs (e.g., tetrahedral molecules like CH₄) and decrease as lone pairs are introduced.

EXPLANATION:

• NH₃: Ammonia has a trigonal pyramidal shape with one lone pair on the nitrogen atom. The lone pair-bond pair repulsion reduces the bond angle from the ideal tetrahedral value of 109.5° to approximately 107°.
  
• NH₄⁺: The ammonium ion has a perfect tetrahedral geometry with no lone pairs on the central nitrogen atom. The bond angle is 109.5°.
• CH₄: Methane also has a tetrahedral geometry with no lone pairs on the central carbon atom. The bond angle is 109.5°.
  
• Since NH₃ has one lone pair, the lone pair-bond pair repulsion reduces its bond angle to 107°, making it the lowest among the options provided.
• NH₂^-
• 

Therefore, the molecule with the lowest bond angle is NH2-, and the correct answer is Option 3.

CONCEPT:

The structure of coordination compounds

• The geometry of a coordination compound is determined by the arrangement of ligands around the central metal atom or ion, based on the coordination number.
• In coordination chemistry, the coordination number refers to the number of ligand donor atoms directly bonded to the central metal atom or ion.
• Common geometries include tetrahedral, octahedral, trigonal bipyramidal, and pentagonal bipyramidal, depending on the coordination number and electronic configuration of the central atom.

EXPLANATION:

• The given compound is (NH₃)₃CrO₄.
• In this compound:
  • Chromium (Cr) is the central metal atom.
  • There are 3 ammonia (NH₃) ligands and 1 oxo (O₄) group bonded to the chromium atom.
  • The coordination number of chromium is 7 (3 from NH₃ ligands and 4 from the oxo group).

• Coordination number 7 typically leads to a pentagonal bipyramidal geometry.
• In a pentagonal bipyramidal structure:
  • Five ligands form a pentagonal plane around the central atom.
  • Two additional ligands are positioned axially, perpendicular to the pentagonal plane.

Therefore, the structure of (NH₃)₃CrO₄ is pentagonal bipyramidal.

CONCEPT:

Nodal planes in molecular orbitals

• Molecular orbitals are formed by the combination of atomic orbitals and can be bonding, antibonding, or non-bonding.
• The number of nodal planes in a molecular orbital determines the regions where the probability of finding an electron is zero.
• For a π* molecular orbital (antibonding π orbital):
  • A π orbital is formed by the sideways overlap of two p orbitals.
  • The antibonding π* molecular orbital has an additional nodal plane compared to the bonding π molecular orbital.

EXPLANATION:

• In a π molecular orbital:
  • There is 1 nodal plane between the p orbitals (due to their opposite phase).
• In the π* molecular orbital:
  • An additional nodal plane is introduced between the nuclei due to the antibonding nature of the orbital.
  • Thus, the total number of nodal planes in the π* molecular orbital is 2.

Therefore, the correct answer is option 2.

CONCEPT:

Bond Order

Bond Order = (Number of bonding electrons - Number of antibonding electrons) / 2

• The bond order of a molecule is defined as the difference between the number of bonding electrons and antibonding electrons, divided by 2:
• A higher bond order indicates a stronger and shorter bond, while a lower bond order indicates a weaker and longer bond.
• When an electron is removed (oxidation) or added (reduction) to a molecule, the bond order may change depending on whether the electron is removed from or added to a bonding or antibonding molecular orbital.

EXPLANATION:

• For the given options, we will calculate the bond order of the reactant and product:
•  N₂ → N₂⁺
  • N₂ bond order = (14 - 8) / 2 = 3
  • N₂⁺ bond order = (13 - 8) / 2 = 2.5
  • The bond order decreases in this case, so this is incorrect.
•  O₂ → O₂^-
  • O₂ bond order = (10 - 6) / 2 = 2
  • O₂⁺ bond order = (16 - 7) / 2 = 1.5
  • The bond order increases in this case, so this is incorrect.
    
•  NO → NO⁺
  • NO bond order = (10 - 5) / 2 = 2.5
  • NO⁺ bond order = (10 - 4) / 2 = 3
  • The bond order increases in this case, so this is correct.
    
•  NO → NO^-
  • NO bond order = (10 - 5) / 2 = 2.5
  • NO^- bond order = (10 - 6) / 2 = 2
  • The bond order decreases in this case, so this is incorrect.

Correct Answer: Option 3 

CONCEPT:

Dipole Moment (μ)

• The dipole moment (μ) is a measure of the separation of positive and negative charges in a molecule.
• When two equal bond moments (m) are at an angle θ (bond angle), the net dipole moment (μ) can be calculated using vector addition of the individual bond moments.
• The component of each bond moment along the resultant direction contributes to the net dipole moment.

EXPLANATION:

• For two bond moments, the net dipole moment is determined by the equation:

  μ = 2m cos(θ)

• Here:
  • m is the bond moment of each bond.
  • θ is the bond angle between the two bonds.
• However, if the bond angle θ is assumed to be small and only one bond moment is being considered, the dipole moment simplifies to:

  μ = m cos(θ)

• Therefore, the correct answer is Option 1: μ = m cos(θ).

Therefore, the dipole moment is μ = m cos(θ).

Option 3 is correct, i.e. When a hydrogen atom is in between the two highly electronegative atoms.

• There are two types of H bond and they are as follows:
  • Intramolecular hydrogen bond.
  • Intermolecular hydrogen bond.

• Intramolecular hydrogen bond:
  • It is formed when a hydrogen atom is in between the two highly electronegative (F, O, N) atoms present within the same molecule. For example, in o-nitrophenol, the hydrogen is in between the two oxygen atoms.
• Intermolecular hydrogen bond:
  • It is formed between two different molecules of the same or different compounds. For example, H-bond in case of HF molecule, alcohol or water molecules, etc.

The correct answer is 4.

Key Points

• The number of electrons present in the valence shell of the atom is called valance electron.
• The valency of an atom is defined as the combining capacity of an atom, In other word, the number of bonds formed by an atom is also called as valency of that atom.
• The atomic wide variety of Sulphur is sixteen and the variety of electrons in its valence shell is 6.
• Thus each oxygen forms two bonds with the Sulphur atom making its valency 4.

Additional Information

• The valency of nitrogen is 3.
• Magnesium which has an atomic number 2 has a valency of 2.
• Elements with valency 1 are those elements that can either gain one electron or lose one electron in order to have a stable electronic configuration.
  Example- Hydrogen

The correct answer is Dispersion Forces.

Key Points

• It is a type of Van der waal Force.
• London force also known as dispersion forces is instantaneous dipole–induced dipole force.
• London force is the weakest intermolecular force among Vanderwaal Forces.

Additional Information

•  London Dispersion Forces Example
  • The unequal distribution of electrons about the nucleus in an atom can induce some dipole in the atom. When another atom or molecule comes in contact with this induced dipole, it can be distorted which leads to an electrostatic attraction between either atoms or molecules. 
• Van Der Waals forces-
  • Van Der Waals forces are the interactions between atoms and molecules that result in a pull between them. These forces consist of weak intermolecular interacting with each the nearest possible distance. The molecules do not contain any charge.
• Types of Vanderwaal Force-
  • London Dispersion Forces
  • dipole induced dipole
  • Hydrogen Bonding

Concept:​

Fajan's Rule:

• Coulombic attraction between the cations and anions in certain cases leads to the deformation of the ions.
• This deformation caused by one molecule to the other is called polarisation.
• The extent to which the molecule is able to polarise the other is called its polarisation power.
• The extent to which a molecule can get polarised is called its polarisability.
• The rise in deformity of ions may give rise to increased electron density between the ions and this leads to a considerable amount of covalent bonding.

Explanation:

Factors affecting the Covalent / Ionic character of bonds:

• The small size of cation:
  • The smaller the size of the cation, the greater is its covalent character.
• The larger size of the anion: 
  • The larger the size of the anions, the less tightly their electrons will be held by the nucleus and it will be polarised more easily and will thus have more covalent character.
• Larger charge on either of the two ions:
  • With the increase in charge on the ions, electrostatic attraction of the cation for the outer electrons of the anion also increases.
  • Consequently, the covalent character of the bond increases.
  • For example, the covalent character follows the order:  AlCl₃ > MgCl₂ > NaCl.
• ​Electronic configuration of the ions:
  • Out of two ions having the same size and charge, the ion with a pseudo noble gas configuration will have higher polarising power and more covalent character than a cation with a noble gas configuration (i.e., ion having 8 electrons in the outermost shell).
• Polarisability decreases along with a period and increases along with a group.
• Low positive charge and large size of cation and a small charge on anion and small size of anion favor the formation of ionic compounds.
• A high positive charge and small size of cation and a high charge on anion and large size of anion favor the formation of covalent compounds.
• Among the given compounds BeCl2, BaCl2, MgCl2, CaCl2, the cations have the same charge +2, and anions have a net charge of -2.
• All the cations Be⁺², Ba⁺², Mg⁺², Ca⁺² belong to the same group II of the periodic table.
• As we move from Be, Mg, Ca, to Ba down the group, the polarisability decreases as well as the covalent character. Hence, the ionic character increases down the group.
• The most ionic being BaCl₂ and the least ionic being BeCl₂.

Hence, the correct order of ionic character is: BeCl2 < MgCl2 < CaCl2 < BaCl2.

The correct answer is With no electron.

Key Points

• In coordination chemistry, a coordinate covalent bond is also known as a dative bond, dipolar bond, or coordinate bond.
• It is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom.
• The bonding of metal ions to ligands involves this kind of interaction.

Additional Information

• There are three types of bonds:
  • Ionic bond
  • covalent bond
  • co-ordinate bond
• Ionic bonds:
  • They are a particular kind of linkage created by the electrostatic attraction of dipolar ions in a chemical molecule.
  • When the valence (outermost) electrons of one atom are permanently transferred to another atom, a bond of this kind is created.
• Covalent bond:
  • It is formed when two atoms exchange one or more pairs of electrons.
  • The two atomic nuclei are concurrently drawing these electrons to them.
  • When the difference between the electronegativities of two atoms is too tiny for an electron transfer to take place to create ions, a covalent bond is formed.

The correct answer is Hydrogen chloride.Key Points

• Covalent compounds are formed when two or more non-metal atoms share electrons to complete their outermost shell.
• Hydrogen chloride is a covalent compound as it is formed by the sharing of electrons between hydrogen and chlorine atoms.
• Magnesium hydroxide and calcium carbonate are both ionic compounds, as they are formed by the transfer of electrons from a metal atom (magnesium or calcium) to a non-metal atom (oxygen or hydroxide).
• Sodium chloride is also an ionic compound, formed by the transfer of electrons between sodium and chlorine atoms.
• Covalent compounds generally have lower melting and boiling points than ionic compounds, and are often gases or liquids at room temperature.
• Hydrogen chloride is an important industrial chemical used in the production of PVC, refrigerants, and other chemicals.

Additional Information

• Magnesium hydroxide is an important component of antacids and is also used in the production of flame retardants and wastewater treatment.
• Calcium carbonate is found in many natural substances such as limestone, chalk, and marble, and is also used as a dietary supplement and in the production of paper, plastics, and paints.
• Sodium chloride, also known as table salt, is commonly used as a seasoning and preservative in food, as well as in the production of chemicals and textiles.

Concept:

The geometry of a molecule:

• The geometry of a molecule depends on the arrangement of bonds about its centre in space.
• The arrangement further depends on the type of hybridization the centre atom is undergoing.
• The orientation of the hybrid orbitals is different in different cases.
• As bonds are formed via overlap of these orbitals, the bonds have directional nature.
• Therefore, hybridization is directly linked to the geometry of the molecule.

Hybridization and bond angles:

• According to VSEPR theory, the electron groups arrange themselves around each other so as to minimize repulsion.
• The electron group includes the bond pairs as well as lone pairs of electrons.
• If repulsion is more, the energy of the system is raised and the molecule becomes unstable.
• So, the arrangement in which there is minimum repulsion and maximum attraction is the most stable structure.
• The arrangement in space gives some angles between the central atom and the bonded atoms which are known as the bond angles.

Few types of hybridization, their modes of mixing, and geometry of molecules are-

Explanation:

• In CO, the structure is:
  : C ≡ O :
• There exist three bonds between carbon and oxygen out of which one is sigma and two are pi.
• So, two pi bond corresponds to 'sp' hybridization.
• The sigma bond between the two atoms is made by the head-on overlap of 2p - 2p orbitals of Carbon and Oxygen.
• The pi bonds are formed by the lateral overlap between p orbitals of carbon and oxygen.

Hence, the mode of hybridization of carbon in CO is 'sp'.

Additional Informationsp Hybridisation of carbon:

• The bond between two C atoms includes two pi and one sigma.
• A pi bond is formed by pure p-p overlap.
• One sigma bond exists between each carbon and hydrogen.
• A total of two sigma bonds means sp hybridization and linear geometry.

sp² Hybridisation of carbon:

• The bond between two C atoms includes one pi and one sigma.
• A pi bond is formed by pure p-p overlap.
• This type of hybridization is seen in alkenes.
• The geometry is trigonal planar.

sp³ Hybridisation of carbon:

• Only sigma bonds are formed by the carbon atoms.
• The geometry is tetrahedral.

Graphite layers are held together by van der Waals forces and not by carbon-carbon single bonds. Hence, 2 is correct and 4 is incorrect.

• Diamond is a covalent solid with each carbon atom covalently bonded to four other carbon atoms situated around it tetrahedrally, forming four single bonds. Hence, statement 1 is correct.
• Graphite has a layered structure having rings of six carbon atoms that are arranged in a widely spaced horizontal plane. Hence, 2 and 3 are correct.

Concept:

 According to Fajan's rule:

• The smaller the cation, the bigger the anion, and the more the covalent character.
• Bigger cations and smaller anions will favor ionic character.

Explanation:

In the given options all have the same anion (Cl^-), the character of the compounds decided by cation only.

Na, K, Li, and Cs belong to I group and their order of atomic size is:

Li < Na < K < Cs.

According to Fajan's rule: Bigger cations and smaller anions will favor ionic character.

So, CsCl has maximum ionic character.

The correct answer is 10.

Key Points

• The atoms must be arranged in a precise way that will permit the orbitals to overlap in order for a covalent connection to form.
• Due to the fact that sigma bonds are more powerful than pi- bonds, it is challenging to break one.
• Sigma bonds are created by the alignment of atomic orbitals along the axis, and pi bonds are created by the alignment of two atomic orbital lobes.
• Propane, C₃H₈, contains 10 sigma bonds altogether, consisting of 2C-C bonds and 8C-H bonds.
• As seen in the picture, propane contains ten covalent bonds. 
• 

Additional Information:

• The three-carbon alkane propane has the chemical formula C₃H₈.
• At room temperature and pressure, it is a gas, but it can be compressed into a liquid for transportation.
• It is a by-product of the processing of natural gas and the refining of petroleum and is frequently utilised as a fuel in home, commercial, and low-emission transportation systems.
• It was found in 1857 by French scientist Marcellin Berthelot, and by 1911 it was sold commercially in the US.
• One of a category of liquefied petroleum gases is propane (LP gases).