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

Select  the incorrect statement.

  1. Double bond is shorter than a single bond
  2. $\sigma$-bond is weaker than a $\pi$-bond

  3. Double bond is stronger than a single bond

  4. Covalent bond is stronger than hydrogen bond
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A sigma bond is generally stronger than a pi bond because of greater orbital overlap. Therefore, the statement that a sigma bond is weaker than a pi bond is incorrect.

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 has $p _{\pi}-d _{\pi}$ bonding?

  1. $NO _3^-$
  2. $SO _3^{2-}$
  3. $BO _3^{3-}$
  4. $CO _3^{2-}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$p \pi-p \pi$ bonding: If there is bonding between two atoms where one atom is having one vacant orbital and another is having one lone pair of electrons, then this electron pair is donated to that respective vacant orbital. This type of bonding is called $p \pi-p \pi$   or $p \pi-d \pi$ depending on the orbital to which the electron pair is donated and from which the electron pair is donated.

In the above options $SO _3^{-2}$ forms $p \pi-p \pi$ bonding.
Hence option $B$ 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 statement is not correct for sigma and pi-bonds formed between two carbon atoms?

  1. A sigma bond is stronger than a pi-bond.

  2. Bond energies of sigma and pi-bonds are of the same order.

  3. Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond.

  4. A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A) A sigma bond is stronger than a pi-bond. This is because sigma bond is formed by axial overlap and pi bond is formed by lateral overlap. Thus the extent of overlap is greater in sigma bond formation than in pi bond formation.
Hence, the option A is correct.
B) Bond energy of sigma bond is higher than that of pi bond as sigma bond is stronger than pi bond.
Hence, the option B is incorrect.
C) Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond. When the carbon atoms of sigma bond are rotated, the axial overlap is not affected. but in case of pi bonds, the lateral overlap will be affected.
Hence, the option C is correct.
D) A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard. A pi bond is present only when a sigma bond is already present.
hence, the option D 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

In allene structure, three carbon atoms are joined by :

  1. three $\sigma$- and three $\pi$-bond
  2. two $\sigma$- and one $\pi$-bond
  3. two $\sigma$- and two $\pi$ - bonds
  4. three $\pi$- bonds only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Allene is $CH _{2}\, =\, C\, =\, CH _{2}$.
The terminal carbons each form one $ \sigma$ with the central carbon. The other bond formed by the terminal carbon with the central carbon is a $\pi$ bond. Hence in total there are two $\sigma$- and two $\pi$ - 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

A triple bond is made of :

  1. one $\sigma$- and two $\pi$ - bonds
  2. two $\sigma$- and one $\pi$ - bonds
  3. three $\sigma$- and three $\pi$ - bonds
  4. one $\sigma$- and four $\pi$ - bonds
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A triple bond is made of one $\sigma $-bond and two $\pi$-bonds.

So answer 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

Number of $\sigma$ and $\pi$ bonds present in $CH _3-CH=CH- C \equiv CH$ are:

  1. $10\, \sigma,\, 3\, \pi$
  2. $10\, \sigma,\, 2\, \pi$
  3. $9\, \sigma,\, 2\, \pi$
  4. $8\, \sigma,\, 3\, \pi$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sigma bonds are formed by axial overlap and pi bonds are formed by sideways overlap. total number of bonds are $10\, \sigma,\, 3\, \pi$.

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

In $N _2$ molecule, the atoms are bonded by:

  1. $1$ $\sigma$ and $2$ $\pi$ - bonds, $2$ L.P.
  2. $1$ $\sigma$ and $1$ $\pi$ - bonds, $1$ L.P.
  3. $2$ $\sigma$ and $1$ $\pi$ - bonds, No L.P.
  4. $1$ $\sigma$, $2$ $\pi$, and No L.P.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
${ N } _{ 2 }$ molecule contains $2$ lone pairs and $1s$ and $2p$ bonds.
$:N\equiv N:$
A triple bond consist of $1$ sigma and two $pi$ bonds. Lone pair refers to a pair of valence electrons that are not shared with another atom, it is also called non-bonding pair.
Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

Select the correct statement (s) about the compound $NO[BF _4]$

  1. It has 5$\sigma$ and 2$\pi$ bond
  2. Nitrogen - oxygen bond length is higher than nitric oxide $(NO)$

  3. It is a diamagnetic species
  4. $BF$ bond length in this compound is lower than in $BF _3$
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

$NO[BF _4]$ can be separated into $NO^+$ and $BF _4^-$. 
$BF _4^-$ has $4$  bonds, as single bonds between $B$ and $F$.
$NO^+$ has $1$  bonds, $2$ bonds.
It is a diamagnetic species.

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

In the cyclo-$S _8$ molecule of rhombic sulphur, all the $S-S$ bond lengths and all the $S-S-S$ bond angles are respectively (give approximate values): 

  1. $204$ pm and $105^{\circ}$
  2. $102$ pm and $120^{\circ}$
  3. $204$ pm and $180^{\circ}$
  4. $102$ pm and $60^{\circ}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There is a single bond between each pair of $S$ atoms and two non-bonding electron pairs on each $S$ atom.Thus we see four electron domains around each $S$ atom and we would expect a tetrahedral geometry corresponding to $sp^3$ hybridisation which gives us the bond angle around $109^0$.

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

The number of sigma and pi bonds in the structure:
$CH _2\, =\, CH\, -\, C\, \equiv\, CH$

  1. 7 and 3

  2. 6 and 2

  3. 4 and 3

  4. All are sigma bonds
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In $H _{2}C = CH-C\equiv CH$, there are $4: C-H$ sigma bonds and $3: C-C$ sigma bonds, thus it has a total of $7 \sigma$ bonds. Also there are $3 \pi$ bonds in the structure.

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

The number of $\sigma$ bonds and $\pi$-bonds present in $\text{pent-4-en-1-yne}$ is:

  1. $10,3$
  2. $4,9$
  3. $3,10$
  4. $9,4$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$HC\equiv C-{CH} _{2}-CH={CH} _{2}$


$\text{Pent-4-en-1-yne}$

Triple bond between $C$ and $C$ contains one $\sigma$ bond and two $\pi$ bonds. Double bond between $C$ and $C$ contains one $\sigma$ bond and one $\pi$ bond.

Total $\sigma$ bonds$=10$

Total $\pi$ bonds $=3$

Hence, the correct option is $\text{A}$

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

In which of the following molecules/ions are all the bonds not equal?

  1. $BF _4^-$
  2. $SF _4$
  3. $SiF _4$
  4. $XeF _4$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In SF4, the sulfur atom has one lone pair and four bonding pairs (seesaw geometry). Due to the lone pair-bond pair repulsion, the bond lengths are not all equal.

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

Strength of pi bonds are generally :

  1. stronger than sigma bond

  2. weaker than sigma bond

  3. stronger than ionic bond

  4. weaker than hydrogen bond
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Strength of pi bond is weaker than sigma bond because it is formed due to lateral overlapping of atomic orbitals. 
Since, their is a sharing of electron between the two atoms, which is not in case of hydrogen bond, hence it is stronger than the hydrogen bond.
Ionic bonds are always stronger than the covalent bonds. Since, Pi bonds are covalent bonds hence, it is weaker than ionic bonds.