Chemistry

Chemical Bonding and Molecular Structure

1,420 Questions

This section tests your knowledge of chemical bonding, molecular structure, and hybridization. It covers ionic and covalent bonds, octet rule exceptions, and molecular geometry. These chemistry questions are common in various competitive entrance examinations.

Ionic and covalent bondsHybridisation of elementsOctet rule exceptionsMolecular geometryIntermolecular forces

Chemical Bonding and Molecular Structure Questions

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following does not have a metal-carbon bond:

  1. $C _{2}H _{5}MgBr$
  2. $K\left [ Pt \left ( C _{2}H _{4} \right ) Cl _{3}\right ]$
  3. $Ni\left ( CO \right ) _{4}$
  4. $Al\left ( OC _{2}H _{5} \right ) _{3}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal.

$C _2H _5MgBr$ is a $\sigma$-bonded complexes.
$K[Pt(C _2H _4)Cl _3]$ contains a bond between carbon and potassium which is a metal.
$Ni(CO) _4$ also contains metal-carbon bond as it is itself a metal carbonyl.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds
The π acid ligands donate their lone pairs to the metal to form a normal σ bond with the latter in addition to it, the vacant orbitals accept e− from the filled metal orbitals to form a type of π−bond which supplements the σ bond.

Which of the following has lowest C-O bond length ?
  1. $[Ni(CO) _4]$
  2. $[Co(CO) _4]^{-}$
  3. $[Fe(CO) _4]^{2-}$
  4. $[Mn(CO) _6]^+$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This type of bonding where a metal is bonded with the carbon of a carbonyl compound is known as synergic bonding. In a metal carbonyl, the M-C bond has both σ and π character. The ligand donates eΘ pair to the central metal atom, and simultaneously accepts eΘ pair from central metal atom through synergic bonding. Here, all the options are examples of organometallic compounds. Due to synergic bonding, the metal carbon bond strength increases and bond length decreases due to the partial double bond character. Thus, the C-O bond strength decreases and bond length increases and bond order of CO decreases as the number of antibonding electrons increase. Out of the four options, the option D has Mn+, implying that the electron donating nature among the options is minimum. Therefore, tendency of synergic bonding is minimum, and thus M-C bond length is maximum implying that C-O bond strength is maximum and C-O bond length is minimum.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following is/are example( s) of $\sigma$-bonded organometallic compound ? 

  1. Al$ _2$(CH$ _3$)$ _6$
  2. Pb(CH$ _3$)$ _4$
  3. Zn(C$ _2$H$ _5$)$ _2$

  4. Ferrocene
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Option (A),(B),(C) are correct.Ferrocene is example of organometallic compound but is not $\sigma$-bonded. Its formula is $Fe(C _5H _5) _2$. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds. Each cyclopentadienyl (Cp) ring is then allocated a single negative charge, bringing the number of -electrons on each ring to six, and thus making them aromatic. These twelve electrons (six from each ring) are then shared with the metal via covalent bonding. 

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following statement(s) is/are incorrect ? 

  1. Metal carbonyls are the examples of only $\sigma$-bonded organometallic complexes.
  2. Metal carbonyls are the examples of only $\pi$-bonded organometallic complexes.
  3. Metal carbonyls are the examples of organometallic complexes which involve both $\sigma$- and $\pi$-bonds between metal and carbon of the carbonyl group.
  4. Metal carbonyls involve both $\sigma$- and $\pi$-bonds between metal and oxygen of the carbonyl group.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

Metal carbonyls involve synergistic bonding where the metal donates electrons into the CO pi-antibonding orbital (pi-backbonding) and CO donates electrons into the metal d-orbitals (sigma-bonding). Therefore, they are not examples of only sigma or only pi bonded complexes, making statements A, B, and D incorrect.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

If the bond length of $CO$ bond in carbon monoxide is 1.128 $\overset{o}A$, then what is the value of $CO$ bond length in $Fe$$(\mathrm{C}\mathrm{O}) _{5}$? 

  1. 1.15 $\overset{o}A$
  2. 1.128 $\overset{o}A$
  3. 1.72 $\overset{o}A$
  4. 1.178 $\overset{o}A$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The metal (Fe) makes the back bonding to CO. The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and the metal (Fe).Which results in the contraction of CO bond length.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

If in the mixed carbonyl, the other ligand is also pi acceptor, it would compete with the ligand CO for gaining the metal $d _\pi$ electron charge. The higher is the extent of back donation in CO, the lesser will be the stretching vibration frequency for C-O bond. If $PF _3$ is better $\pi$-acceptor than CO, then answer the following.


Select the correct order of stretching vibration frequency C-O bond in the following molecules :

  1. $[Ni(CO) _4] > [Ni(PF _3)(CO) _3]$
  2. $[Ni(CO) _4] < [Ni(CO) _3 (PF _3)]$
  3. $[Ni(CO) _4] = [Ni(PF _3)(CO) _3]$

  4. Can not predicted
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If $PF _3$ is a better $\pi$-acceptor ligand than CO, then
extent of back donation from $M \overset{\pi}{\rightarrow} C \equiv O$ decreases, and hence bond order of CO will less decrease.
Stretching frequency of C - O bond $\propto$ bond order of C $\equiv$ O.
Therefore, stretching frequency of $[Ni(PF _3)(CO) _3] >  [Ni(CO) _4]$.

Multiple choice salts salts and their classification acids, bases and salts chemistry

What additional factors affect the rate of dissolution of ionic solids like salts?

  1. Enthalpy and entropy

  2. Enthalpy and surface area

  3. Entropy and temperature

  4. Enthalpy and temperature
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Enthalpy and temperature affect the rate of dissolution of ionic solids like salts.
Positive value of enthalpy change indicates that the dissolution of ionic salt is endothermic. Increasing temperature will increase the dissolution of ionic solids like salts.

On the other hand,
negative value of enthalpy change indicates that the dissolution of ionic salt is exothermic. Increasing temperature will decrease the dissolution of ionic solids like salts.
Hence, option (D) is the correct answer.

Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

2 mole of ${ H } _{ 3 }{ PO } _{ 4 }$ has:

  1. Two $\pi $-bond
  2. Seven mole of $\sigma $-bond

  3. Sixteen lone pair of electron
  4. Fourteen mole of $\sigma $-bond
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

H3PO4 structure: P is double bonded to one O (1 pi bond) and single bonded to three OH groups. Total bonds: 3 P-O, 3 O-H, 1 P=O. Total sigma bonds = 3+3+1 = 7 per molecule. For 2 moles, 14 moles of sigma bonds.

Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

Which of the following is not correct?

  1. A sigma bond is weaker than pi bond.

  2. A sigma bond is stronger than pi bond.

  3. A double bond is stronger than a single bond.

  4. A double bond between two atoms is shorter than a single bond between the same atoms.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A sigma bond is stronger than a $\pi$ bond due to axial overlapping of the orbitals.

A double bond is stronger than a single bond since now more energy is required to break two bonds.
Double bonds are $sp^2$ hybridized and are shorter in length.
Hence, the correct option is A.

Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

Give the number of $\sigma$ and $\pi$ bonds in (i)$C^{2-} _2$ (ii)$C _3^{4-}$ and (iii)$CN^{2-} _2.$

  1. (i) 2 $\sigma$, 1 $\pi$; (ii) 1 $\sigma$, 3 $\pi$; (iii) 2 $\sigma$, 2 $\pi$
  2. (i) 2 $\sigma$, 1 $\pi$; (ii) 3 $\sigma$, 1 $\pi$; (iii) 2 $\sigma$, 2 $\pi$
  3. (i) 1 $\sigma$, 2 $\pi$; (ii) 2 $\sigma$, 2 $\pi$; (iii) 2 $\sigma$, 2 $\pi$
  4. (i) 1 $\sigma$, 2 $\pi$; (ii) 3 $\sigma$, 1 $\pi$; (iii) 2 $\sigma$, 2 $\pi$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$(i)^{-}\textrm{C}\equiv C^-$  one $\sigma$, two $\pi$;  (ii) $^{-}\textrm{C}\equiv C-C^{3-}$ two $\sigma$, two $\pi$;   (iii) $^{-}\textrm{N}=C=N^-$ two $\sigma$, two $\pi$
Hence option C is correct.

Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

Which of the following compound has a lowest nitrogen-nitrogen bond length?


     $N _2,  N _2H _2,  N _2F _2$.

  1. $N _2$
  2. $N _2H _2$
  3. $ N _2F _2$

  4. All have equal bond length.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

N2 has a triple bond (bond order 3), N2H2 has a double bond (bond order 2), and N2F2 has a double bond. Higher bond order results in shorter bond length.