Classification of Elements and Periodicity in Properties Set-2

Question 1

How is the covalent radius of a non-metallic element like Chlorine calculated?

Accepted Answer

Half the distance between two atoms when they are bound by a single covalent bond

Answer

The full internuclear distance between the atoms

Answer

Half the internuclear distance in a metallic crystal

Answer

Half the van der Waals radius

Question 2

The metallic radius of Copper ($	ext{Cu}$) is assigned a value of $128	ext{ pm}$. This is based on the internuclear distance of $256	ext{ pm}$ between adjacent $	ext{Cu}$ atoms in the solid crystal, where the metallic radius is:

Accepted Answer

Half the internuclear distance

Answer

Twice the internuclear distance

Answer

Equal to the internuclear distance

Answer

$256	ext{ pm}$

Question 3

Why does atomic size generally decrease across a period (left to right)?

Accepted Answer

Effective nuclear charge increases, increasing attraction of electrons to the nucleus within the same valence shell

Answer

Effective nuclear charge decreases.

Answer

The principal quantum number ($n$) increases.

Answer

The number of core electrons increases drastically.

Question 4

Why does the atomic radius increase as we descend a group?

Accepted Answer

The valence electrons are placed farther from the nucleus due to increased principal quantum number ($n$) and shielding

Answer

The nuclear charge decreases down the group.

Answer

The electron gain enthalpy becomes more negative.

Answer

All inner energy levels are completely filled.

Question 5

When comparing the size of an anion ($	ext{X}^-$) to its parent atom ($	ext{X}$), the anion is:

Accepted Answer

Larger, because the added electron increases repulsion and decreases effective nuclear charge

Answer

Smaller, due to increased effective nuclear charge

Answer

Smaller, because it has more protons

Answer

The same, as the nuclear charge is constant

Question 6

An atom ($	ext{X}$) forms a cation ($	ext{X}^+$). Which statement correctly describes the relationship between their sizes?

Accepted Answer

The cation is smaller because it has fewer electrons while the nuclear charge remains the same

Answer

The cation is larger because the remaining electrons are less attracted by the nucleus.

Answer

The cation is the same size because only valence electrons are involved.

Answer

The cation's radius is half the atomic radius.

Question 7

Consider the isoelectronic species $	ext{O}^{2-}, 	ext{F}^{-}, 	ext{Na}^{+}, 	ext{Mg}^{2+}$. Which ion has the largest radius?

Accepted Answer

$	ext{O}^{2-}$ (Anion with greater negative charge has larger radius due to net electron repulsion)

Answer

$	ext{Mg}^{2+}$

Answer

$	ext{Na}^{+}$

Answer

$	ext{F}^{-}$

Question 8

Which isoelectronic species will have the smallest radius among $	ext{N}^{3-}, 	ext{O}^{2-}, 	ext{F}^{-}$?

Accepted Answer

$	ext{F}^{-}$

Answer

$	ext{N}^{3-}$

Answer

$	ext{O}^{2-}$

Answer

All are the same size

Question 9

Arrange the following isoelectronic species in the order of increasing ionic radii: $	ext{Mg}^{2+}, 	ext{Na}^{+}, 	ext{F}^{-}$.

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 10

Why are the atomic radii of noble gases not typically compared with the covalent radii of other elements?

Accepted Answer

They are monoatomic, and their non-bonded (van der Waals) radii values are typically very large

Answer

They are highly reactive.

Answer

Their atomic numbers are too high.

Answer

They are located in the $p$-block.

Question 11

In the sequence $	ext{Mg}, 	ext{Mg}^{2+}, 	ext{Al}, 	ext{Al}^{3+}$, identify the species with the largest size.

Accepted Answer

$	ext{Mg}$ (Largest parent atom)

Answer

$	ext{Mg}^{2+}$

Answer

$	ext{Al}$

Answer

$	ext{Al}^{3+}$

Question 12

The ionic radius of Fluoride ion ($	ext{F}^{-}$) is $136	ext{ pm}$, while the atomic radius of Fluorine ($	ext{F}$) is $64	ext{ pm}$. This drastic increase in size is primarily due to:

Accepted Answer

Increased electron-electron repulsion and decrease in effective nuclear charge

Answer

Decrease in nuclear charge

Answer

The loss of the valence shell

Answer

The electron entering the $n=3$ quantum level

Question 13

Which of the following elements, $	ext{Li}, 	ext{Na}, 	ext{K}, 	ext{Rb}, 	ext{Cs}$, has the largest atomic radius?

Accepted Answer

$	ext{Cs}$

Answer

$	ext{Rb}$

Answer

$	ext{K}$

Answer

$	ext{Li}$

Question 14

Considering elements $	ext{Na, Mg, Al, Si, P, S, Cl}$ (Period 3), which element has the smallest atomic radius?

Accepted Answer

$	ext{Cl}$

Answer

$	ext{Na}$

Answer

$	ext{Si}$

Answer

$	ext{Mg}$

Question 15

The species $	ext{Ar}, 	ext{K}^{+}, 	ext{Ca}^{2+}$ are isoelectronic. The correct order of their radii (from smallest to largest) is:

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 16

Ionization Enthalpy ($\Delta_i H$) is the energy required to remove an electron from an atom in which specific state?

Accepted Answer

Isolated gaseous atom in its ground state

Answer

Liquid atom

Answer

Solid crystal lattice

Answer

Gaseous ion in an excited state

Question 17

The second ionization enthalpy ($\Delta_i H_2$) is always higher than the first ionization enthalpy ($\Delta_i H_1$) because:

Accepted Answer

It is more difficult to remove an electron from a positively charged ion than from a neutral atom

Answer

It is easier to remove an electron from a positively charged ion than from a neutral atom.

Answer

Energy is always required to remove electrons from an atom.

Answer

Effective nuclear charge decreases after the first removal.

Question 18

On a plot of first ionization enthalpies ($\Delta_i H$) versus atomic number ($Z$), where do the maxima (highest values) occur?

Accepted Answer

At the noble gases

Answer

At the alkali metals

Answer

At the halogens

Answer

At the alkaline earth metals

Question 19

Why does ionization enthalpy generally increase across a period?

Accepted Answer

Successive electrons are added to orbitals in the same principal quantum level, and increasing nuclear charge outweighs shielding

Answer

Increase in shielding outweighs the increase in nuclear charge.

Answer

The valence electrons are increasingly farther from the nucleus.

Answer

The principal quantum number ($n$) decreases.

Question 20

The first ionization enthalpy of Boron ($	ext{Z}=5$) is slightly less than that of Beryllium ($	ext{Z}=4$) because:

Accepted Answer

The $2p$ electron in $	ext{B}$ is more shielded by inner core electrons than the $2s$ electron in $	ext{Be}$, making it easier to remove

Answer

The $2s$ electron in $	ext{Be}$ is more shielded than the $2p$ electron in $	ext{B}$.

Answer

$	ext{Be}$ has a higher atomic number.

Answer

$	ext{B}$ has a completely filled $2s$ orbital.

Question 21

The "anomaly" of Oxygen ($	ext{O}$) having a smaller first ionization enthalpy than Nitrogen ($	ext{N}$) arises because:

Accepted Answer

Oxygen has increased electron-electron repulsion due to paired electrons in a $2p$-orbital, making removal easier

Answer

Oxygen has a lower nuclear charge.

Answer

Nitrogen has a completely filled $2p$ subshell.

Answer

Oxygen is more electronegative than Nitrogen.

Question 22

The first ionization enthalpy values for $	ext{Na}, 	ext{Mg}$, and $	ext{Si}$ are $496, 737$, and $786	ext{ kJ mol}^{-1}$ respectively. Based on shielding and orbital configuration, the first $\Delta_i H$ value for $	ext{Al}$ should be closest to: (Hard Level)

Accepted Answer

$575	ext{ kJ mol}^{-1}$ (Lower than $	ext{Mg}$ due to effective shielding of $3p$ electron by $3s$ electrons)

Answer

$760	ext{ kJ mol}^{-1}$

Answer

$490	ext{ kJ mol}^{-1}$

Answer

$737	ext{ kJ mol}^{-1}$

Question 23

For an element with the electronic configuration $	ext{1s}^2 	ext{2s}^2 	ext{2p}^6 	ext{3s}^1$, which ionization enthalpy will show a significantly large jump in value?

Accepted Answer

$\Delta_i H_2$ (Removal breaks into the stable noble gas core, $[	ext{Ne}]$)

Answer

$\Delta_i H_1$

Answer

$\Delta_i H_3$

Answer

$\Delta_i H_4$

Question 24

The valence electron in Lithium ($	ext{Li}$) is shielded from the nucleus by the inner core of $1s$ electrons. The reduction in the effective nuclear charge experienced by this valence electron is known as:

Accepted Answer

Shielding or Screening

Answer

Electronegativity

Answer

Ionization Potential

Answer

Penetration Effect

Question 25

The ionization enthalpies generally decrease down a group primarily because:

Accepted Answer

The outermost electron is increasingly farther from the nucleus, and increased shielding outweighs the increasing nuclear charge

Answer

Effective nuclear charge increases significantly.

Answer

The atomic radius decreases.

Answer

The number of valence electrons increases.

Question 26

An element $	ext{I}$ has $\Delta_i H_1 = 520	ext{ kJ mol}^{-1}$ and a very high $\Delta_i H_2 = 7300	ext{ kJ mol}^{-1}$. Which statement is true about element $	ext{I}$?

Accepted Answer

It is an Alkali Metal (Group 1)

Answer

It is the least reactive element.

Answer

It forms a stable binary halide $	ext{MX}_2$.

Answer

It is a Noble Gas.

Question 27

An element $	ext{VI}$ has $\Delta_i H_1 = 738	ext{ kJ mol}^{-1}$ and $\Delta_i H_2 = 1451	ext{ kJ mol}^{-1}$. This small difference between $\Delta_i H_1$ and $\Delta_i H_2$ suggests that element $	ext{VI}$ is likely to be:

Accepted Answer

An alkaline earth metal (forms stable $	ext{M}^{2+}$ ion)

Answer

A noble gas

Answer

An alkali metal

Answer

A halogen

Question 28

What is the correct order of the first ionization enthalpy for the second period elements $	ext{Li, Be, B}$?

Accepted Answer

$	ext{Li} < 	ext{B} < 	ext{Be}$

Answer

$	ext{Li} < 	ext{Be} < 	ext{B}$

Answer

$	ext{B} < 	ext{Be} < 	ext{Li}$

Answer

$	ext{Be} < 	ext{B} < 	ext{Li}$

Question 29

When considering the elements $	ext{B, Al, Mg,}$ and $	ext{K}$, what is the correct order of their metallic character (from least metallic to most metallic)?

Accepted Answer

$	ext{B} < 	ext{Al} < 	ext{Mg} < 	ext{K}$

Answer

$	ext{K} < 	ext{Mg} < 	ext{Al} < 	ext{B}$

Answer

$	ext{B} < 	ext{Mg} < 	ext{Al} < 	ext{K}$

Answer

$	ext{Al} < 	ext{B} < 	ext{Mg} < 	ext{K}$

Question 30

Which statement regarding ionization enthalpy is incorrect?

Accepted Answer

The removal of an electron from orbitals bearing lower $n$ value is easier than from an orbital having higher $n$ value

Answer

Ionization enthalpy increases for each successive electron removed.

Answer

A big jump in ionization enthalpy marks the end of valence electrons.

Answer

The greatest increase in ionization enthalpy occurs upon removal of an electron from the core noble gas configuration.

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Classification of Elements and Periodicity in Properties Set-2

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