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Formal charge - class-XI

Description: formal charge
Number of Questions: 15
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Tags: chemical bonding and structure chemical bonding chemical bonding and molecular structure chemistry
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Effective charge on each oxygen is $-\frac{1}{4}$ in?

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $SO _{3}^{2-}$

  2. $SO _{3-}^{4}$

  3. $ClO _{3}^{-}$

  4. $ClO _{4}^{-}$

Show answer
Correct Option: C

Among ${ KO } _{ 2 },{ AIO } _{ 2 }^{ - },{ BaO } _{ 2 }\ and\ { NO } _{ 2 }^{ + }$, unpaired electron is present in :

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. ${ NO } _{ 2 }^{ + }\quad and\quad { BaO } _{ 2 }$

  2. ${ KO } _{ 2 }\quad and\quad AI{ O } _{ 2 }^{ - }$

  3. ${ KO } _{ 2 }$ only

  4. $Ba{ O } _{ 2 }$ only

Show answer
Correct Option: C
Explanation:

This can be done by counting number of valence electrons


$KO _2=1+2\times 6=17$-Odd number of electrons and hence unpaired.


$AlO^{2-} _2=3+2\times 6+1=14$-Even number of electrons and hence paired.

$BaO _2=2+2\times6=14$-Even number of electrons and hence paired.

$NO^{+} _{2}=5+2\times6 -1=16$-Even number of electrons and hence paired.

Hence option C is the correct answer.

Which has highest specific charge?

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $Na^{+}(mass\ no\ =23)$

  2. $Mg^{2+}(mass\ no\ =24)$

  3. $Al^{+3}(mass\ no\ =27)$

  4. $Si^{+4}(mass\ no\ =28)$

Show answer
Correct Option: D
Explanation:

Specific charge in the ratio of charge of ion to its mass.

Specific charge $=\dfrac { e }{ M } $
For ${ Na }^{ + }=\dfrac { e }{ 23 } ,\quad $ for ${ Mg }^{ 2+ }=\dfrac { 2\times e }{ 24 } $
For ${ Al }^{ 3+ }=\dfrac { 3\times e }{ 27 } ,\quad $ for ${ Si }^{ 4+ }=\dfrac { 4\times e }{ 28 } $
In is in the following order,
${ Si }^{ 4+ }>{ Al }^{ 3+ }>{ Mg }^{ 2+ }>{ Na }^{ + }$

In bisulphate ion, the formal charge on sulphur atom is:

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $+1$

  2. $+2$

  3. $+4$

  4. $+6$

Show answer
Correct Option: B

Formal charge on nitrogen and oxygen in $NO^- _3$ ion are respectively: 

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $0, \dfrac{-1}{3}$

  2. $+1, \dfrac{-1}{3}$

  3. $+1, \dfrac{-2}{3}$

  4. $0, \dfrac{-2}{3}$

Show answer
Correct Option: A
Explanation:

Formula change is basically a change given to an atom, on assuming that the electrons in a chemical bond are shared equally between the atoms, neglecting theirrelative, $EN.$

$FC=V-N-\cfrac{B}{2}$       $(V=\text{no. of valance electron}\N=\text{No. of non bonding electrons}\B=\text{No. of electrons in covalent bond})$
$FC$ on $N$ in $NO^- _3=0$
$FC$ on $O$ in $NO _3^-=\cfrac{-1}{3}$

Which of the following given below is incorrect :

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. ONF is isoelectronic with ${O _2}{N^ - }$

  2. ${\rm{O}}{{\rm{F}} _2}$ is an oxide of fluorine

  3. $C{l _2}{O _7}$ is an anhydride of perchloric acid

  4. ${O _3}$ molecule is bent

Show answer
Correct Option: A

The bond order in $N _{2}$ is 

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. 2

  2. 2.5

  3. 1.5

  4. 3

Show answer
Correct Option: D

Formal charge on nitrogen in $NO _{3}^{-}$ ion is

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $+1$

  2. $+2$

  3. $+5$

  4. $Zero$

Show answer
Correct Option: A

The formal charge on the O atoms in the ion $[:\ddot{O} = N = \ddot{O}:]^+$ is:

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $-2$

  2. $-1$

  3. $0$

  4. $+1$

Show answer
Correct Option: C
Explanation:

Formal charge$=$Valence electrons-non bonding electrons+no of bonds$ =6-(4+2)=0$

In the cyanide ion the formal negative charge is on:

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $C$

  2. $N$

  3. both $C$ and $N$

  4. resonate between $C$ and $N$

Show answer
Correct Option: D
Explanation:

In the cyanide ion the formal negative charge resonates between $C$ and $N$. Cyanide ion has resonating structure, $-\overset { \ _ }{ C } \equiv N\longleftrightarrow \overset { \ _ }{ N } \underrightarrow { = } C$

In which of the following molecules, is the covalent bond most polar?

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. HI

  2. HBr

  3. HCl

  4. HF

Show answer
Correct Option: A
Explanation:

Polar covalent bond shows minimum electronegativity difference between the atoms.

$H=2.1,F=4,Cl=3,Br=2.8,I=2.5.$ 

So, $HI=0.4$ with the minimum difference is the most polar covalent bond.

Hence, option A is correct.

A molecule with highest bond energy is:

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. Fluorine

  2. Chlorine

  3. Bromine

  4. Iodine

Show answer
Correct Option: B
Explanation:

Bond dissociation energy in $KJ mol^-1$
$F _2-158$
$Cl _2-244$ 
$Br _2-93$ 
$I _2-151$ 
Hence, in order of decreasing bond strength: 
$Cl _2>Br _2>F _2>I _2$
Fluorine is an anomaly. 

Bond strength decreases from chlorine to iodine as down the group, the atomic size becomes larger and thus the valence electron orbitals become more diffused, causing the overlap of orbitals to become less effective. Therefore the halogen-halogen bond becomes weaker from chlorine to iodine.Fluorine is an exception due to its extremely small size. The F-F bond length is so short that the lone pairs of electrons on the fluorine atoms repel each other and weakens the F-F bond. 

In which of the following molecules partial charge separation does not take place?

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. Chlorine

  2. Hydrochloric acid

  3. Water

  4. Ammonia

Show answer
Correct Option: A
Explanation:

Cl molecules are covalent in nature so it is non polar molecule. Non polar compound consists of molecules linked through chemical bonds arranged in such a way that the distribution of charges are symmetrical. Non polar bonds do not exhibit polarity and do not form ions in their solution. These compounds do not dissolve in water which is a polar molecule.

The partial charge separation between the bonded atoms gives rise to ___________ in that compound.

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. covalent character

  2. coordinate character

  3. ionic character

  4. none of these

Show answer
Correct Option: C
Explanation:

Partial charge separation between the bonded atoms gives rise to ionic character in the molecule due to the electronegativity difference, a quite small degree of polarization occurs.

What is the formal charge on the chlorine atom in the oxyacid $HOClO _2$ if it contains single bonds ?

chemistry chemical bonding and structure formal charge basics of chemical bonding types of bonds

  1. $-2$

  2. $-1$

  3. $+1$

  4. $+2$

Show answer
Correct Option: D
Explanation:

formal charge= valence electrons-(lone electrons+bonds)
$=7-(2+3)=+2$

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