Classification of Elements and Periodicity in Properties Set-3

Question 1

Electron Gain Enthalpy ($\Delta_{eg} H$) is defined as the enthalpy change accompanying the process where a neutral gaseous atom ($	ext{X}$) forms:

Accepted Answer

$	ext{X}^{-}(	ext{g})$

Answer

$	ext{X}^{+}(	ext{g}) + e^{-}$

Answer

$	ext{X}^{2+}(	ext{g}) + 2e^{-}$

Answer

$	ext{X}(	ext{l})$

Question 2

Group 17 elements (Halogens) have highly negative electron gain enthalpies because:

Accepted Answer

They can attain a stable noble gas electronic configuration by picking up one electron

Answer

They are located on the left side of the periodic table.

Answer

They have high ionization enthalpies.

Answer

They are large atoms.

Question 3

Why do Noble Gases have large **positive** electron gain enthalpies?

Accepted Answer

The added electron must enter the next higher principal quantum level ($n+1$), leading to a very unstable electronic configuration

Answer

They are monatomic.

Answer

They have small atomic radii.

Answer

Their ionization enthalpy is very low.

Question 4

Among $	ext{P, S, Cl, F}$, which element will have the **most** negative electron gain enthalpy ($\Delta_{eg} H$)?

Accepted Answer

$	ext{Cl}$ (Due to the larger $3p$ orbital accommodating the electron with less repulsion than $2p$ of $	ext{F}$)

Answer

$	ext{F}$

Answer

$	ext{P}$

Answer

$	ext{S}$

Question 5

Why is the electron gain enthalpy of Oxygen ($	ext{O}$) less negative than that of Sulfur ($	ext{S}$)?

Accepted Answer

The added electron in $	ext{O}$ goes to the small $n=2$ quantum level and suffers significant electron-electron repulsion

Answer

$	ext{S}$ has a much smaller atomic radius than $	ext{O}$.

Answer

$	ext{O}$ is located lower in the group than $	ext{S}$.

Answer

$	ext{O}$ has a half-filled $p$-orbital.

Question 6

What is the fundamental difference between Electron Gain Enthalpy and Electronegativity?

Accepted Answer

$\Delta_{eg} H$ measures energy change for an isolated gaseous atom forming an anion, while electronegativity is a measure of an atom's ability to attract **shared** electrons in a compound

Answer

Electronegativity is a measureable quantity, while $\Delta_{eg} H$ is not.

Answer

Both measure the tendency to gain electrons, but $\Delta_{eg} H$ is qualitative.

Answer

$\Delta_{eg} H$ is expressed on the Pauling scale, while electronegativity is in $	ext{kJ mol}^{-1}$.

Question 7

Electronegativity generally increases across a period because:

Accepted Answer

The atomic radius decreases and the attraction between the valence electrons and the nucleus increases

Answer

The size of the atom increases.

Answer

Metallic properties increase.

Answer

Ionization enthalpy decreases.

Question 8

Which scale, used to quantify electronegativity, arbitrarily assigned a value of $4.0$ to Fluorine?

Accepted Answer

Pauling scale

Answer

Mulliken-Jaffe scale

Answer

Allred-Rochow scale

Answer

Dobereiner scale

Question 9

Which of the following sets of elements exhibits the strongest tendency to form an anion (i.e., highest non-metallic character)?

Accepted Answer

$	ext{F, Cl, Br}$ (Group 17, Halogens)

Answer

$	ext{Na, Mg, Al}$

Answer

$	ext{Si, P, S}$

Answer

$	ext{C, N, O}$

Question 10

The second electron gain enthalpy of Oxygen ($	ext{O}^{-} 	o 	ext{O}^{2-}$):

Accepted Answer

Must be positive (endothermic), requiring energy to overcome repulsion between the incoming electron and the existing negative charge

Answer

Must be highly negative.

Answer

Must be zero.

Answer

Is approximately equal to the first electron gain enthalpy.

Question 11

Considering the elements $	ext{F, Cl, O, and N}$, the correct order of their non-metallic character is:

Accepted Answer

$	ext{F} > 	ext{O} > 	ext{N} > 	ext{Cl}$ (Decreases down group, increases across period)

Answer

$	ext{Cl} > 	ext{F} > 	ext{O} > 	ext{N}$

Answer

$	ext{F} > 	ext{N} > 	ext{O} > 	ext{Cl}$

Answer

$	ext{F} > 	ext{O} > 	ext{N} > 	ext{Si}$

Question 12

The least reactive element among $	ext{I, II, III, IV, V, VI}$ (from Problem 3.31), which has a large positive $\Delta_{eg} H$ and very high $\Delta_i H_1$, is likely to be:

Accepted Answer

Element $	ext{V}$ (Noble Gas: $\Delta_i H_1 = 2372, \Delta_{eg} H = +48$)

Answer

Element $	ext{I}$

Answer

Element $	ext{III}$

Answer

Element $	ext{IV}$

Question 13

The most reactive non-metal among $	ext{I, II, III, IV, V, VI}$ (from Problem 3.31), characterized by high $\Delta_i H_1$ and highly negative $\Delta_{eg} H$, is likely to be:

Accepted Answer

Element $	ext{III}$ (Halogen: $\Delta_i H_1 = 1681, \Delta_{eg} H = -328$)

Answer

Element $	ext{IV}$

Answer

Element $	ext{VI}$

Answer

Element $	ext{I}$

Question 14

Based on the values in Table 3.7, which element pair shows the greatest deviation from the expected trend that $\Delta_{eg} H$ becomes less negative down a group?

Accepted Answer

$	ext{O}$ and $	ext{S}$

Answer

$	ext{H}$ and $	ext{Li}$

Answer

$	ext{Cl}$ and $	ext{Br}$

Answer

$	ext{Na}$ and $	ext{K}$

Question 15

The valence of representative elements is usually equal to the number of electrons in the outermost orbitals, or:

Accepted Answer

Eight minus the number of outermost electrons

Answer

Half the atomic number

Answer

The principal quantum number ($n$)

Answer

The group number divided by two

Question 16

An element $	ext{M}$ from Group 2 (Alkaline Earth Metal) combines with an element $	ext{N}$ from Group 15 (Valence 3). Predict the formula of the stable binary compound formed.

Accepted Answer

$	ext{M}_3	ext{N}_2$ (Valences $2$ and $3$)

Answer

$	ext{MN}$

Answer

$	ext{MN}_2$

Answer

$	ext{M}_2	ext{N}_3$

Question 17

The oxide formed by the element on the extreme right of a period, such as $	ext{Cl}_2	ext{O}_7$, is typically:

Accepted Answer

Most acidic

Answer

Neutral

Answer

Amphoteric

Answer

Most basic

Question 18

The anomalous behavior of the first member of groups 1, 2, and 13-17 (e.g., $	ext{Li}, 	ext{Be}, 	ext{B}$) is primarily attributed to their:

Accepted Answer

Small size, large charge/radius ratio, and high electronegativity

Answer

Large size and low electronegativity

Answer

High number of available valence orbitals

Answer

Low ionization enthalpy

Question 19

What is the maximum covalency typically exhibited by the first member of a $p$-block group (e.g., Boron), compared to subsequent members like Aluminium? (Hard Level)

Accepted Answer

4 (due to only four valence orbitals: $2s$ and $2p$)

Answer

6 (due to availability of $d$-orbitals)

Answer

8 (due to expanded octet)

Answer

5 (due to ability to form $p\pi-p\pi$ bonds)

Question 20

An atom has the electronic configuration $	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^2 	ext{3p}^6 	ext{3d}^3 	ext{4s}^2$. It will be placed in which group?

Accepted Answer

$	ext{Fifth}$ (5th)

Answer

$	ext{Third}$ (3rd)

Answer

$	ext{Fourth}$ (4th)

Answer

$	ext{Sixth}$ (6th)

Question 21

The correct order of first ionization energy enthalpy ($	ext{IE}_1$) for the given four elements ($	ext{C, O, N, F}$) is:

Accepted Answer

$	ext{C} < 	ext{O} < 	ext{N} < 	ext{F}$

Answer

$	ext{C} < 	ext{N} < 	ext{O} < 	ext{F}$

Answer

$	ext{F} < 	ext{N} < 	ext{O} < 	ext{C}$

Answer

$	ext{C} < 	ext{O} < 	ext{F} < 	ext{N}$

Question 22

The correct order of atomic radii in Group $13$ element ($	ext{B, Al, Ga, In, Tl}$) is:

Accepted Answer

$	ext{B} < 	ext{Ga} < 	ext{Al} < 	ext{In} < 	ext{Tl}$

Answer

$	ext{B} < 	ext{Al} < 	ext{Ga} < 	ext{In} < 	ext{Tl}$

Answer

$	ext{Tl} > 	ext{In} > 	ext{Al} > 	ext{Ga} > 	ext{B}$

Answer

$	ext{B} < 	ext{Al} < 	ext{In} < 	ext{Ga} < 	ext{Tl}$

Question 23

The species $	ext{Ar, K}^+, 	ext{Ca}^{2+}$ contain the same number of electrons. In which order do their radii increase?

Accepted Answer

$	ext{Ca}^{2+} < 	ext{K}^+ < 	ext{Ar}$

Answer

$	ext{K}^+ < 	ext{Ar} < 	ext{Ca}^{2+}$

Answer

$	ext{Ar} < 	ext{K}^+ < 	ext{Ca}^{2+}$

Answer

$	ext{Ar} < 	ext{Ca}^{2+} < 	ext{K}^+$

Question 24

Which of the following order of ionic radius is correctly represented?

Accepted Answer

$	ext{None of the above}$

Answer

$	ext{H}^+ > 	ext{H} > 	ext{H}^-$

Answer

$	ext{Na}^+ < 	ext{F}^- < 	ext{O}^{2-}$

Answer

$	ext{O}^{2-} < 	ext{F}^- < 	ext{Na}^+$

Question 25

Which one of the following arrangements represents the correct order of least negative to most negative electron gain enthalpy ($\Delta_{	ext{eg}} 	ext{H}$) of $	ext{C, Ca, Al, F, and O}$?

Accepted Answer

$	ext{Ca} < 	ext{Al} < 	ext{C} < 	ext{O} < 	ext{F}$

Answer

$	ext{F} > 	ext{O} > 	ext{C} > 	ext{Al} > 	ext{Ca}$

Answer

$	ext{Ca} < 	ext{C} < 	ext{O} < 	ext{Al} < 	ext{F}$

Answer

$	ext{Al} < 	ext{Ca} < 	ext{C} < 	ext{O} < 	ext{F}$

Question 26

Identify the wrong statement in the following:

Accepted Answer

Among isoelectronic species, **smaller the positive charge** on the cation, **smaller** is the ionic radius.

Answer

Among isoelectronic species, greater the negative charge on the anion, greater is the atomic/ionic radius.

Answer

Atomic radius of the element increases as one moves down the first group of the periodic table.

Answer

Atomic radius of the element decreases as one moves across from left to right in the second period of the periodic table.

Question 27

Among the element $	ext{Ca, Mg, P, Cl}$, the order of increasing atomic radii is:

Accepted Answer

$	ext{Cl} < 	ext{P} < 	ext{Mg} < 	ext{Ca}$

Answer

$	ext{Cl} < 	ext{P} < 	ext{Ca} < 	ext{Mg}$

Answer

$	ext{Ca} < 	ext{Mg} < 	ext{P} < 	ext{Cl}$

Answer

$	ext{Mg} < 	ext{Ca} < 	ext{Cl} < 	ext{P}$

Question 28

Identify the correct order of increasing ionic size for the following isoelectronic species: $	ext{Ca}^{2+}, 	ext{K}^+, 	ext{Ar}, 	ext{Cl}^-, 	ext{S}^{2-}$.

Accepted Answer

$	ext{Ca}^{2+} < 	ext{K}^+ < 	ext{Ar} < 	ext{Cl}^- < 	ext{S}^{2-}$

Answer

$	ext{S}^{2-} < 	ext{Cl}^- < 	ext{Ar} < 	ext{K}^+ < 	ext{Ca}^{2+}$

Answer

$	ext{Ar} < 	ext{K}^+ < 	ext{Ca}^{2+} < 	ext{Cl}^- < 	ext{S}^{2-}$

Answer

$	ext{Cl}^- < 	ext{S}^{2-} < 	ext{Ar} < 	ext{K}^+ < 	ext{Ca}^{2+}$

Question 29

Which electronic configuration indicates that there will be an abnormally high difference in the second ($	ext{IE}_2$) and third ($	ext{IE}_3$) ionization enthalpy of the element?

Accepted Answer

$	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^2$

Answer

$	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^1$

Answer

$	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^2 	ext{3p}^1$

Answer

$	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^2 	ext{3p}^2$

Question 30

The first ionization enthalpy (in $	ext{eV}$) for Beryllium ($	ext{Be}$) and Boron ($	ext{B}$) respectively, are:

Accepted Answer

$9.32, 8.29$

Answer

$8.29, 9.32$

Answer

$9.32, 9.32$

Answer

$10.00, 10.00$

Question 31

Which one of the following ions will be the smallest in size?

Accepted Answer

$	ext{Mg}^{2+}$

Answer

$	ext{Na}^+$

Answer

$	ext{O}^{2-}$

Answer

$	ext{F}^-$

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Classification of Elements and Periodicity in Properties Set-3

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