jee main chemistry important questions | Classification Of Elements And Periodicity In Properties

Q 1 :

Given below are two statements:

Statement I: The correct order of first ionization enthalpy values of Li, Na, F and Cl is Na < Li < Cl < F.

Statement II: The correct order of negative electron gain enthalpy values of Li, Na, F and Cl is Na < Li < F < CI

In the light of the above statements, choose the correct answer from the options given below : [2024]

Both Statement I and Statement II are true
Both Statement I and Statement II are false
Statement I is true but Statement II is false
Statement I is false but Statement II is true

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(1)

Statement (l): Ionization energy decreases down the group and increases from left to right across a period. Hence order is $Na < Li < Cl < F .$

Statement (II): Electron affinity decreases (or electron gain enthalpy becomes less negative) down the group and increases (or electron gain enthalpy becomes more negative) from left to right across a period. But electron gain enthalpy of F is less negative than that of Cl. This is because due to small size of F, incoming electron,feels significant repulsion from other electrons. So, the order is $Na < Li < F < Cl .$

Q 2 :

The electron affinity value are negative for

A.    $Be \to {Be}^{-}$

B.    $N \to N^{-}$

C.    $O \to O^{2 -}$

D.    $Na \to {Na}^{-}$

E.    $Al \to {Al}^{-}$

Choose the most appropriate answer from the options given below:   [2024]

A, B and C only
D and E only
A and D only
A, B, D and E only

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(1)

Electron affinity is negative for Be, Mg, N and noble gases. So (A) and (B) has negative value of electron affinity. Sum of first and second electron affinity for every element is negative. So (C) has negative electron affinity.

Q 3 :

Given below are two statements :

Statement (I): The oxidation state of an element in a particular compound is the charge acquired by its atom on the basis of electron gain enthalpy consideration from other atoms in the molecule.

Statement (II): $p π - p π$ bond formation is more prevalent in second period elements over other periods.

In the light of the above statements, choose the most appropriate answer from the options given below: [2024]

Both Statement I and Statement II are incorrect
Both Statement I and Statement II are correct
Statement I is incorrect but Statement II is correct
Statement I is correct but Statement II is incorrect

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(3)

Statement I: The oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms were fully ionic i.e. shift the bond pair of electrons towards more electronegative atom, the charge acquired after this shift is oxidation number of the atom. Hence oxidation number is charge acquired on the basis of electronegativity difference.

Statement II: Because of small size, strength of $p π - p π$ bonds in second period elements is more, hence $p π - p π$ bonds are more prevalent in second period elements,

Q 4 :

Given below are two statements:

Statement I: Fluorine has most negative electron gain enthalpy in its group.
Statement II: Oxygen has least negative electron gain enthalpy in its group.

In the light of the above statements, choose the most appropriate from the options given below. [2024]

Statement I is false but Statement II is true
Both Statement I and Statement II are true
Both Statement I and Statement II are false
Statement I is true but Statement II is false

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(1)

Q 5 :

Given below are two statements:

Statement I: The radii of isoelectronic species increases in the order. ${Mg}^{2 +} < {Na}^{+} < F^{-} < O^{2 -}$

Statement II: The magnitude of electron gain enthalpy of halogen decreases in the order. $Cl > F > Br > I$

In the light of the above statements, choose the most appropriate answer from the options given below: [2025]

Both Statement I and Statement II are incorrect
Statement I is correct but Statement II is incorrect
Statement I is incorrect but Statement II is correct
Both Statement I and Statement II are correct

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(4)

Statement I:

For isoelectronic species, $r \propto \frac{1}{Z}$

Statement II: Electron affinity decreases down the group because as we move down the group, incoming electron is added farther away from the nucleus hence feels less attraction. However, electron affinity of F is less than expected value because of inter-electronic repulsion faced by the incoming electron on account of extremely small size of F.

Q 6 :

For electron gain enthalpies of the elements denoted as $Δ_{eg} H$ , the incorrect option is: [2023]

$Δ_{eg} H (Cl) < Δ_{eg} H (F)$
$Δ_{eg} H (I) < Δ_{eg} H (At)$
$Δ_{eg} H (Te) < Δ_{eg} H (Po)$
$Δ_{eg} H (Se) < Δ_{eg} H (S)$

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(4)

Negative electron gain enthalpy of Cl is more than F.

Negative electron gain enthalpy of S is more than Se.

Q 7 :

The difference between electron gain enthalpies will be maximum between: [2023]

Ar and Cl
Ne and Cl
Ne and F
Ar and F

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(2)

Cl has maximum –ve $Δ H_{e g}$ and Ne has most +ve $Δ H_{e g}$ , hence difference will be maximum for Ne and Cl.

Element	${ΔH}_{eg} (kJ / mole)$
F	– 333
Cl	– 349
Ne	+ 48
Ar	+ 116

Q 8 :

Given below are two statements :

Statement I : C < O < N < F is the correct order in terms of first ionization enthalpy values.

Statement II : S > Se > Te > Po > O is the correct order in terms of the magnitude of electron gain enthalpy values.

In the light of the above statements, choose the correct answer from the options given below : [2026]

Both Statement I and Statement II are false
Both Statement I and Statement II are true
Statement I is false but Statement II is true
Statement I is true but Statement II is false

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(2)

$Statement-I is correct$

$\begin{matrix} S & > & Se & > & Te & > & Po & > & O \\ | Δ_{eg} H | & 200 & 195 & 190 & 174 & 141 (in kJ/mol) \end{matrix}$

$Statement-II is correct.$

Q 9 :

Correct electron gain enthalpy order is

Ne > S > F > Cl
He > Ne > Ar = Kr > Xe
O > S > Ne > He
Ne > S > Cl > F

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(1)

$S = - 200$

$F = - 333$

$C l = - 349$

$N e = + ve value$

Q 10 :

The formation of the oxide ion $O^{2 -} (g)$ , from oxygen atom requires first an exothermic and then an endothermic step as shown below:

$O_{(g)} + e^{-} \to {O^{-}}_{(g)}; Δ_{1} H ° = - 141 k J m o l^{- 1}$

${O^{-}}_{(g)} + e^{-} \to {O^{2 -}}_{(g)}, Δ_{2} H ° = + 780 k J m o l^{- 1}$

Thus process of formation of $O^{2 -}$ in gas phase is unfavourable even though $O^{2 -}$ is isoelectronic with neon. It is due to the fact that

electron repulsion out weighs the stability gained by achieving noble gas configuration
$O^{-}$ ion has comparatively smaller size than oxygen atom
Oxygen is more electronegative
Addition of electron in oxygen results in larger size of the ion.

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(1)

2nd electron affinity is positive

Q 11 :

With in each pair of elements F and Cl, S and Se, and Li and Na respectively, the elements that release more energy upon an electron gain enthalpy are

F, Se and Na
F, S and Li
Cl, S and Li
Cl, Se and Na

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(3)

The first electron gain enthalpy is exothermic (or negative). Generally, electron gain enthalpy becomes less exothermic (or less negative) when comparing elements of a group from top to bottom.

Therefore, electron gain enthalpy of S > Se and Li > Na.

But there are some exceptions to this.

One of them is the case of group 17 elements where electron gain is most negative for Cl instead of F, due to the extra small size of fluorine.

$∴$ Upon an electron gain, energy releases in the order:

Cl > F, S > Se and Li > Na.

Q 12 :

In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively. [2026]

lowest and lowest
highest and lowest
lowest and highest
highest and highest

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(3)

Ionization energy increases and electron gain enthalpy becomes more negative from left to right across a period. Hence ionization energy of an element at extreme left in a period is lowest. And electron gain enthalpy at extreme end (except noble gas) is most negative.

Topic Question Set

Q 2 :

The electron affinity value are negative for

A.    $Be \to {Be}^{-}$

B.    $N \to N^{-}$

C.    $O \to O^{2 -}$

D.    $Na \to {Na}^{-}$

E.    $Al \to {Al}^{-}$

Choose the most appropriate answer from the options given below:   [2024]

Q 4 :

Given below are two statements:

Statement I: Fluorine has most negative electron gain enthalpy in its group.
Statement II: Oxygen has least negative electron gain enthalpy in its group.

In the light of the above statements, choose the most appropriate from the options given below. [2024]

Q 6 :

For electron gain enthalpies of the elements denoted as $Δ_{eg} H$ , the incorrect option is: [2023]

Q 7 :

The difference between electron gain enthalpies will be maximum between: [2023]

Q 9 :

Correct electron gain enthalpy order is

Q 11 :

With in each pair of elements F and Cl, S and Se, and Li and Na respectively, the elements that release more energy upon an electron gain enthalpy are

Q 12 :

In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively. [2026]

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Topic Question Set

Q 2 : The electron affinity value are negative for A. Be→Be- B. N→N- C. O→O2- D. Na→Na- E. Al→Al- Choose the most appropriate answer from the options given below: [2024]

Q 4 : Given below are two statements: Statement I: Fluorine has most negative electron gain enthalpy in its group. Statement II: Oxygen has least negative electron gain enthalpy in its group. In the light of the above statements, choose the most appropriate from the options given below. [2024]

Q 6 : For electron gain enthalpies of the elements denoted as ΔegH, the incorrect option is: [2023]

Q 7 : The difference between electron gain enthalpies will be maximum between: [2023]

Q 9 : Correct electron gain enthalpy order is

Q 11 : With in each pair of elements F and Cl, S and Se, and Li and Na respectively, the elements that release more energy upon an electron gain enthalpy are

Q 12 : In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively. [2026]

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Q 2 :

The electron affinity value are negative for

A. $Be \to {Be}^{-}$

B. $N \to N^{-}$

C. $O \to O^{2 -}$

D. $Na \to {Na}^{-}$

E. $Al \to {Al}^{-}$

Choose the most appropriate answer from the options given below: [2024]

Q 4 :

Given below are two statements:

Statement I: Fluorine has most negative electron gain enthalpy in its group.
Statement II: Oxygen has least negative electron gain enthalpy in its group.

In the light of the above statements, choose the most appropriate from the options given below. [2024]

Q 6 :

For electron gain enthalpies of the elements denoted as $Δ_{eg} H$ , the incorrect option is: [2023]

Q 7 :

The difference between electron gain enthalpies will be maximum between: [2023]

Q 9 :

Correct electron gain enthalpy order is

Q 11 :

With in each pair of elements F and Cl, S and Se, and Li and Na respectively, the elements that release more energy upon an electron gain enthalpy are

Q 12 :

In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively. [2026]