Chemistry

Chemical Bonding and Molecular Structure

1,277 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 the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which of the following statement is/are correct regarding $B _{2}H _{6}$?

  1. Banana bonds are longer but stronger than normal $B-H$ bonds
  2. $B _{2}H _{6}$ is also known $3c-2e$ compound
  3. The hybrid state of B in $B _{2}H _{6}$ is $sp^{3}$ while that of $sp^{2}$ in $BH _{3}$
  4. It cannot be prepared by reacting $BF _{3}$ with $LiBH _{3}$ in the presence of dry ether
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

In which of the following molecules is hydrogen bond absent?

  1. Water

  2. Inorganic benzene

  3. Diborane

  4. Methanol
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As there is no lone pair of electrons present on the boron in diborane it do not form a hydrogen bond.But in water inorganic benzene and methanol there is a lone pair of electrons on oxygen, nitrogen and oxygen respectively so they form hydrogen bonding between most electronegative atom like nitrogen oxygen and hydrogen.
Hence option $D$ is correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which of the following molecular hydride acts as a lewis acid?

  1. $CH _4$
  2. $NH _3$
  3. $H _2O$
  4. $B _2H _6$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$B _2H _6$ is a electron deficient molecule so it acts like an acid(acid is the substance which accepts the pair of electrons). $CH _4,NH _3,H _2O$ allare having lone pairs on central atoms.
Hence option D is correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which one of the following molecular hydrides acts as a Lewis acid?

  1. NH$ _{3}$
  2. H$ _{2}$O
  3. B$ _{2}$H$ _{6}$
  4. CH$ _{4}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
According to the definition a molecule which can accept a lone pair is called a lewis acid.
$A)$ Ammonia has a lone pair on nitrogen,so it can donate the lone pair rather than accepting a lonepair.So,it is a lewis base.
$B)$Water has $2$ lone pairs on oxygen so it cannot accept any further lonepairs,so water is a lewis base not a lewis acid.
$C)$In diborane the bonds found are banana bonds or tau bonds so it has a tendency to accept a lone pair because it has empty orbitals.So it can be considered as a lewis acid.
$D)$Carbon usually doesn't accept or donate lonepair,so it is neither a lewis base nor lewis acid.We can consider it as a neutral molecule. 
Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which of the following is not true regarding the nature of halides of boron?

  1. Boron trihalides are covalent.
  2. Boron trihalides are planar triangular with $sp^2$ hybridisation.

  3. Boron trihalides act as Lewis acids.

  4. Boron trihalides cannot be hydrolysed easily.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Boron trihalides like $BF _{3}$ are covalent in nature. These are forming with $sp^{2}$ hybridization in the shape of triangular planar. All trihalides are strong in acidic nature, as Lewis acids. They react with water to form boric acid. 

The sequence for the Lewis acidity is $BF _{3} < BCl _{3} < BBr _{3}$, where $BBr _{3}$ is the strongest Lewis acid. But these trihalides can be easily hydrolyzed except $BF _3$ due to the highly stable nature of $BF _3$.

Thus option D is correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Hydrogen form a 'bridge' in the chemical structure of which of the following compound?

  1. Hydrogen peroxide

  2. Diborane

  3. Ice

  4. Lithium hydride
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In $B _2H _6$,the bonding between the boron atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the terminal hydrogen atoms, each boron has one valence electron remaining for additional bonding. The bridging hydrogen atoms provide one electron each. Thus the $B _2H _2$ ring is held together by four electrons, an example of 3-center 2-electron bonding. This type of bond is sometimes called a 'banana bond'.

Hence option B is correct answer.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Select the correct statement(s):

  1. The crystal structure of $NaHCO _3$ and $KHCO _3$ both show hydrogen bonding, but are different. In $NaHCO _3$ the $HCO^{-} _{3}$ ions are linked into an infinite chain, while in $KHCO _3$ a dimeric anion is formed.
  2. The $BeX _2$ molecules polymerize to form chains containing bridging halogen groups; for example, in $(BeF _2) _n$ and $(BeCl _2) _n$ each halogen from one normal covalent bond and use a lone pair to form a co-ordinate bond.
  3. $[Be(Me _2) _n]$ has essentially the same structure as $(BeCl _2) _n$ but the bonding in the methyl compound is best regarded as three center two electron bonds covering one $Me$ and $Be$ atoms.
  4. Beryllium salts are acidic when dissolved in pure water because the hydrated ion hydrolyzed producing $H _3O^+$.
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

(A) Even though both sodium bicarbonate and potassium bicarbonate shows hydrogen bonding in the  crystal structure, sodium bicarbonate forms a polymer and potassium bicarbonate forms a dimer.
Hence, the option A is correct.
(B)  Beryllium dihalide is a polymer in which halogen atoms acts as bridges between two Be atoms.
Thus, each halogen atom forms two bonds, one is coordinate and the other is covalent.
Thus, the option B is correct.
(C) The polymeric dimethyl beryllium and the polymeric beryllium dichloride have similar structures involving bridging but in polymeric dimethyl beryllium, each methyl group form bridges with two Be atoms. These bridges are 3 C - 2 e bonds.
Thus, the option C is correct.
(D) Beryllium ion on hydration forms protonium ion. Hence, beryllium salts are acidic.
$Be^{2+} + 2H-OH \rightarrow Be(OH)^+ +H _3O^+$.
Hence, the option D is correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which of the following statements(s) is/are correct?

  1. $B _2H _6$ is non-planar
  2. $B _2H _6$ is polar
  3. $B _2H _6$ is $e^-$ deficient
  4. $B _2H _6$ has two $3C-2e^-$ bond
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

Diborane is non-planar molecule as each $B$ atom has tetrahedral geometry.It is electron deficient molecule as each $B$ atom has only $6$ valence electrons. It contains two $3C-2e$ bonds.
Thus, all the options are correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Select the correct statement(s).

  1. In diborane 12 valence $e^-$ are involved in bonding

  2. In diborane, maximum six atoms, two boron and four terminal hydrogen, lie in the same plane.

  3. Diborane has ethane-like structure

  4. In diborane, bridging bonds are stronger and longer than the terminal bonds.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

Diborane is an electron deficient molecule. The two boron atoms and the four terminal hydrogen atoms of the molecule are in the same plane. The bridging hydrogen atoms lie above and below this plane. The four B-H bonds are regular 2-centered 2-electron bonds. The bridging B-H bonds are unusual 3-centered 2-electron bonds. There are 12 valence electrons, out of them 8 are used in four non bridging hydrogen bonds and other 4 are shared in forming 2-centered 2-electron bond. The bridging hydrogen bonds are stronger that means the bridging H-atoms can not be replaced in chemical reactions. The lengths of these bonds are $1.33 A°$ which is longer than that of terminal $H-$bond $1.19A°$. This is because of the electrostatic repulsion felt by the positively charged nuclei of the two hydrogen atoms that form the hydrogen bridge will cause the bond to be bent- referred to as a "banana bond".

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which of the following statements(s) is/are correct?

  1. Dipole moment of diborane is zero

  2. Diborane is lewis acid

  3. Diborane has incomplete octet
  4. Diborane has four $2C-2e^-$ bond
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

Diborane is the chemical compound consisting of boron and hydrogen with the formula $B _2H _6$.In diborane, boron is $sp^3$ hybridized and each boron is attached to two hydrogens through two centres two-electron bond ($2C-2e^-$ bond) and to another two hydrogens (bridging hydrogen) through three centres two electron bonds ($3C-2e^-$ bond). $BH _3$ (monomer of $B _2H _6$), is an electron-deficient molecule (i.e. the boron is surrounded by only six electrons; not eight). It means $B _2H _6$ is surrounded by $12$ electrons not with $16$ electrons(electron deficient molecule is Lewis acid). And the dipole moment is zero. 

Hence options $A,\ B,\ C$ and $D$ are correct.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

The type of hybridisation of boron in diborane is :

  1. $sp$
  2. $sp^2$
  3. $sp^3$
  4. $dsp^2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Boron has three valence electrons, so it is supposed to make 3 bonds in a molecule with hybridization, $sp^{2}$ as only s and two p orbitals are used in hybridization and last p orbitalis vacant.

But diborane, $B _{2}H _{6}$ contains two electrons each, three centred bonds. Each Boron atom is in a link with four hydrogen atoms. This makes tetrahedral geometry. 

Hence, each Boron atom is $sp^{3}$ - hybridized.

The correct option is C.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

Which among the following is not a borane?

  1. $B _2H _6$
  2. $B _3H _6$
  3. $B _4H _10$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Boranes comprise a large group of the group 13 hydride compounds with the generic formula of $B _xH _y$.
Following are the general formulae of boranes. So $B _3H _6$ is not a borane as it does not hold the formulae of boranes.
Hence option $B$ is correct.

Multiple choice chemistry pollution of air and water environmental impact: global warming green house effect geobiochemical cycle

Which of the following is not a refrigerant?

  1. $CHClF _{2}$
  2. $NH _{3}$
  3. $Ether$
  4. $C _{2}H _{4}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Ethene is a colorless flammable gas with a faint "sweet and musky" odor when pure.
Ethylene is widely used in chemical industry. Ethylene is also an important natural plant hormone, used in agriculture to force the ripening of fruits. it is a non refrigerant.

Multiple choice chemistry chemistry of non-metals oxides of elements simple oxides oxygen

Which of the following statements are not correct ?

  1. All C - O bonds in $CO _3^{2-}$ are equal but not in $H _2CO _3$
  2. All C - O bonds in $HCO _2^-$ are equal but not in $HCO _2H$.
  3. C - O bond length in $HCO _2^-$ is longer than C - O bond length in $CO _3^{2-}$
  4. C - O bond length in $HCO _2^-$ and C - O bond length in $CO _3^{2-}$ are equal
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In HCO2- (formate ion), the C-O bond length is an average due to resonance, but it is generally shorter than a single bond and longer than a double bond. Comparing it to CO3(2-), the bond lengths are similar due to resonance, making statement C incorrect.