Ionic (Electrovalent) Bonding and Properties of Ionic Compounds Practice Questions — JAMB UTME

Question 1Question →

An element $X$ with atomic number $12$ combines with an element $Y$ with atomic number $17$ to form a solid compound. Which of the following statements correctly accounts for the electrical conductivity of this compound?

It conducts electricity in the molten state because the giant ionic lattice breaks down, allowing the ions to move freely.

It conducts electricity in the solid state because delocalized valence electrons migrate freely through the crystal lattice.

It does not conduct electricity when dissolved in water because polar solvent molecules neutralize ionic charges.

It conducts electricity in the solid state because covalent electron sharing forms continuous conductive pathways.

Show answer & explanation

Answer: It conducts electricity in the molten state because the giant ionic lattice breaks down, allowing the ions to move freely.

Answer

The compound conducts electricity in the molten state because the giant ionic lattice breaks down, allowing the ions to move freely.

In solid electrovalent compounds, ions are locked into fixed lattice coordinates by strong electrostatic attraction and cannot migrate. Heating the compound until it melts breaks down the lattice, liberating the cations and anions so they can move freely under an applied electrical potential.

Step-by-Step Solution

1

Determine the type of bonding present in the compound formed by

X

and

Y

.

Element

X

(atomic number 12) has an electronic configuration of

2,8,2

(metal). Element

Y

(atomic number 17) has an electronic configuration of

2,8,7

(non-metal). Metal

X

transfers 2 electrons to two atoms of non-metal

Y

, forming an electrovalent (ionic) compound

XY_2

consisting of

X^{2+}

and

Y^-

ions.

Electrovalent bonding occurs between electropositive metals and electronegative non-metals via full electron transfer.

2

Evaluate the state of charge carriers in the solid state versus the molten state.

In the solid state, strong electrostatic forces hold

X^{2+}

and

Y^-

ions in rigid, fixed lattice positions, so no charge carriers can move. In the molten state, heat breaks the lattice, enabling the ions to move freely toward oppositely charged electrodes.

Electrical conduction requires mobile charge carriers. In ionic substances, these carriers are mobile ions present only in liquid (molten) or aqueous states.

Key Concept

Ionic bonding and electrical conductivity of ionic compounds

Question 2Question →

Magnesium oxide ( $MgO$ ) has a significantly higher melting point than sodium chloride ( $NaCl$ ) because the electrostatic forces of attraction between its divalent ions ( $Mg^{2+}$ and $O^{2-}$ ) are substantially stronger than those between the monovalent ions ( $Na^+$ and $Cl^-$ ).

True

False

Show answer & explanation

Answer: True

Answer

True

The statement is true because the electrostatic force holding an electrovalent lattice together scales with the product of the ionic charges. Divalent magnesium (

Mg^{2+}

) and oxide (

O^{2-}

) ions form a lattice with much higher lattice energy than monovalent sodium (

Na^+

) and chloride (

Cl^-

) ions, giving magnesium oxide a much higher melting point.

Step-by-Step Solution

1

Determine the ionic charges of the component ions in both compounds

MgO

is composed of

Mg^{2+}

and

O^{2-}

ions (divalent), while

NaCl

is composed of

Na^+

and

Cl^-

ions (monovalent).

The magnitude of ionic charges directly dictates the strength of electrostatic forces in an electrovalent crystal lattice.

2

Apply Coulomb's Law to compare lattice attraction strength

The attraction force scales with the charge product: for

MgO

,

|(+2) \times (-2)| = 4

; for

NaCl

,

|(+1) \times (-1)| = 1

.

A fourfold increase in charge product produces significantly stronger ionic bonds and greater lattice energy.

3

Correlate lattice energy with melting point

Greater thermal energy is required to overcome the electrostatic forces in

MgO

than in

NaCl

, resulting in a vastly higher melting point.

Melting point directly reflects the energy required to break down the solid giant ionic lattice structure.

Key Concept

Lattice Energy and Ion Charge Dependency in Ionic Compounds

Question 3Question →

An element $M$ forms a stable electrovalent chloride with the formula $MCl_2$ . If the dipositive cation $M^{2+}$ has the electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6$ , which of the following statements correctly explains the electrical conductivity and lattice properties of $MCl_2$ ?

It does not conduct electricity in the solid state because its ions are held in fixed positions, but conducts in the molten state due to mobile

M^{2+}

and

Cl^-

ions.

It conducts electricity in both the solid and molten states because delocalized valence electrons move freely through the ionic crystal lattice.

It has a low melting point and conducts electricity in the solid state because

M^{2+}

cations migrate easily between lattice nodes.

It conducts electricity when molten because the neutral compound dissociates into free electrons and uncharged elemental atoms.

Show answer & explanation

Answer: It does not conduct electricity in the solid state because its ions are held in fixed positions, but conducts in the molten state due to mobile $M^{2+}$ and $Cl^-$ ions.

Answer

The compound does not conduct electricity in the solid state because its ions are held in fixed positions within the lattice, but conducts in the molten state due to mobile

M^{2+}

and

Cl^-

ions.

In giant electrovalent (ionic) lattices like

CaCl_2

, ions are immobilized in fixed positions in the solid state, making the solid a non-conductor. Upon melting, the electrostatic lattice forces are overcome, producing free mobile

M^{2+}

and

Cl^-

ions that conduct electricity.

Step-by-Step Solution

1

Identify the element and ion structure

The ion

M^{2+}

has 18 electrons (

1s^2 2s^2 2p^6 3s^2 3p^6

), corresponding to a neutral calcium atom (

Ca

, atomic number 20). The compound formed is calcium chloride (

CaCl_2

).

Determining the electronic structure confirms

MCl_2

is a typical giant ionic (electrovalent) lattice.

2

Analyze solid-state properties

In the solid state,

M^{2+}

cations and

Cl^-

anions are locked in a rigid three-dimensional crystal lattice by strong omnidirectional electrostatic forces of attraction. Because the ions cannot move, the solid is an electrical insulator.

Conduction of electricity requires mobile charge carriers.

3

Analyze molten-state properties

When heated to its high melting point, thermal energy overcomes the lattice energy, allowing the

M^{2+}

and

Cl^-

ions to move freely and carry electrical current.

Liquid ionic compounds conduct electricity via migration of ions toward oppositely charged electrodes.

Key Concept

Ionic Lattice Properties and Conduction Mechanism

Question 4Question →

Which of the following best explains why solid sodium chloride ( $NaCl$ ) does not conduct electricity, whereas molten sodium chloride conducts electricity readily?

In the solid state, the ions are held in fixed positions within the crystal lattice and cannot move freely.

Solid sodium chloride consists of neutral molecules, whereas molten sodium chloride breaks into free electrons.

Electrons are transferred from sodium to chlorine only when the compound is heated into the molten state.

The ionic bonds in sodium chloride solid are covalent, but they turn electrovalent when melted.

Show answer & explanation

Answer: In the solid state, the ions are held in fixed positions within the crystal lattice and cannot move freely.

Answer

In the solid state, the ions are held in fixed positions within the crystal lattice and cannot move freely.

Ionic (electrovalent) compounds conduct electricity only when charge carriers (ions) are free to move. In the solid state, ions are locked tightly into fixed positions within the giant ionic lattice, preventing electrical conduction. When melted, the high thermal energy breaks the rigid lattice structure, enabling the positive (

Na^+

) and negative (

Cl^-

) ions to move freely and carry electrical current.

Step-by-Step Solution

1

Identify the nature of charge carriers in ionic compounds.

Electrical conductivity in electrovalent (ionic) compounds relies on mobile ions (

Na^+

and

Cl^-

), not free electrons.

Ionic compounds do not contain free delocalized electrons like metals.

2

Analyze the structural state of solid sodium chloride.

In solid

NaCl

, electrostatic forces lock ions in fixed positions in a giant 3D crystal lattice structure.

Because ions cannot move from place to place, solid

NaCl

acts as an electrical insulator.

3

Compare the solid state with the molten state.

When melted (molten state), thermal energy overcomes the rigid lattice forces, allowing

Na^+

and

Cl^-

ions to move freely toward electrodes.

Mobile ions enable the flow of electric current in the liquid/molten state.

Key Concept

Electrical Conductivity of Electrovalent Compounds

Question 5Question →

Magnesium oxide ( $MgO$ ) has a significantly higher melting point ( $2,852^\circ\text{C}$ ) than sodium fluoride ( $NaF$ ) ( $996^\circ\text{C}$ ) primarily because the product of the ionic charges in $MgO$ is four times greater than in $NaF$ , resulting in stronger electrostatic forces within the crystal lattice. Is this statement true or false?

True

False

Show answer & explanation

Answer: True

Answer

The statement is true because the strength of electrovalent bonding and lattice energy increases proportionally with the product of the ionic charges.

The statement is correct because electrovalent bond strength is governed by Coulomb's Law of electrostatic attraction. Doubly charged cations and anions (

Mg^{2+}

and

O^{2-}

) experience an electrostatic force four times stronger than singly charged ions (

Na^+

and

F^-

) of comparable size, yielding a substantially higher lattice energy and melting point.

Step-by-Step Solution

1

Identify the constituent ions and their respective charges for both ionic compounds.

In

MgO

, the ions are

Mg^{2+}

and

O^{2-}

. In

NaF

, the ions are

Na^+

and

F^-

.

Electrostatic attraction depends fundamentally on the magnitude of nuclear charges transferred during ionic bond formation.

2

Calculate the product of the ionic charges for each compound.

For

MgO

:

|(+2) \times (-2)| = 4

. For

NaF

:

|(+1) \times (-1)| = 1

.

Coulomb's Law states that electrostatic force is proportional to the product of the charges (

q_1 q_2

).

3

Relate the charge product to lattice energy and physical properties such as melting point.

A higher lattice energy requires more thermal energy to break the rigid giant ionic lattice, leading to a much higher melting point for

MgO

than

NaF

.

Melting point directly reflects the magnitude of the electrostatic attraction holding the ions in their solid lattice positions.

Key Concept

Factors Affecting Ionic Lattice Energy and Melting Points

Question 6Question →

Match each observed physical property or phenomenon of ionic (electrovalent) compounds on the left with its correct underlying thermodynamic or structural explanation on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

1 matches with the explanation of charge product dependence on lattice energy; 2 matches with the explanation of Fajans' rules of polarization; 3 matches with the explanation of hydration enthalpy exceeding lattice enthalpy; 4 matches with the explanation of ion mobility in molten versus solid states.

Each physical property directly corresponds to its underlying quantum mechanical or thermodynamic principle: lattice energy scales with charge product (

MgO

vs

NaCl

), polarization of anion electron clouds by small high-charge cations creates covalent character (

AlI_3

), exothermic dissolution occurs when hydration energy exceeds lattice energy (

NaOH

), and electrical conduction requires mobile ions that are locked in solids but liberated upon melting (

CaF_2

).

Step-by-Step Solution

1

Analyze the high melting point of

MgO

versus

NaCl

Lattice energy is governed by Coulomb's law:

E \propto \frac{|q_1 q_2|}{r}

.

MgO

consists of

Mg^{2+}

and

O^{2-}

(product = 4), while

NaCl

consists of

Na^+

and

Cl^-

(product = 1). Higher charge product leads to stronger lattice attraction and a higher melting point.

Identify the primary thermodynamic factor controlling lattice strength in ionic crystals.

2

Analyze the anomalous covalent behavior of

AlI_3

Apply Fajans' rules: Covalency increases with high cation charge density and large anion size.

Al^{3+}

has high charge density and

I^-

is large and easily polarized, leading to electron cloud sharing (covalent character).

Explain deviations from purely electrovalent behavior using polarization principles.

3

Analyze the thermochemistry of dissolution of

NaOH

Dissolution enthalpy

\Delta H_{soln} = \Delta H_{lat} + \Delta H_{hyd}

. If hydration enthalpy released is greater in magnitude than the lattice enthalpy required to separate ions, the net process is exothermic.

Relate lattice energy and hydration energy to dissolution energetics.

4

Analyze electrical conductivity in solid versus molten

CaF_2

Solid ionic compounds contain ions held rigidly in a lattice structure. When melted, thermal energy breaks the lattice, producing free-moving ions capable of carrying electrical current.

Distinguish between mobile charge carriers (molten state) and immobile lattice positions (solid state).

Key Concept

Thermodynamic and structural factors governing ionic lattice stability, polarization (Fajans' rules), solution energetics, and state-dependent conductivity.

Question 7Question →

Consider four main group elements $P$ , $Q$ , $R$ , and $S$ with atomic numbers $11$ , $12$ , $16$ , and $17$ respectively. Which combination of these elements forms an electrovalent compound with the highest melting point?

The combination of

Q

and

S

, because the

+2

and

-2

ionic charges maximize the electrostatic lattice attraction.

The combination of

P

and

R

, because single electron transfer minimizes interionic repulsion within the crystal lattice.

The combination of

Q

and

R

, because a

1:2

stoichiometric ratio produces the highest crystal packing density.

The combination of

P

and

S

, because two

P^+

cations double the total electrostatic pull on a single

S^{2-}

anion.

Show answer & explanation

Answer: The combination of $Q$ and $S$ , because the $+2$ and $-2$ ionic charges maximize the electrostatic lattice attraction.

Answer

The combination of element Q (atomic number 12) and element S (atomic number 16) forms QS, which has the highest melting point due to the +2 and -2 ionic charges maximizing electrostatic lattice attraction.

Element Q (atomic number 12) has electronic configuration 2,8,2 and loses two electrons to form Q2+. Element S (atomic number 16) has electronic configuration 2,8,6 and gains two electrons to form S2-. The compound formed between Q and S (QS) consists of divalent ions. By Coulomb's Law, lattice energy is proportional to the product of ionic charges (|q1 * q2|). The charge product for QS is 4, which is double that of QR2 or P2S (charge product 2) and four times that of PR (charge product 1). Consequently, QS possesses the highest lattice energy and highest melting point.

Step-by-Step Solution

1

Determine the identity and valency of each element from its atomic number

P

(

Z=11

, Sodium) forms

P^+

cations;

Q

(

Z=12

, Magnesium) forms

Q^{2+}

cations;

S

(

Z=16

, Sulfur) forms

S^{2-}

anions;

R

(

Z=17

, Chlorine) forms

R^-

anions.

Electronic configurations determine the number of valence electrons lost or gained to achieve stable octet structures.

2

Write the chemical formulas for the electrovalent compounds formed by valid metal-nonmetal pairs

Possible ionic compounds are

PR

(

P^+ R^-

),

P_2S

(

(P^+)_2 S^{2-}

),

QR_2

(

Q^{2+} (R^-)_2

), and

QS

(

Q^{2+} S^{2-}

).

Electrovalent compounds form when metals transfer electrons to non-metals to achieve electrical neutrality.

3

Compare the electrostatic lattice energies of the resulting crystal lattices

Lattice energy is directly proportional to the product of ionic charges (

E_{\text{lattice}} \propto |q_1 q_2|

). For

QS

,

|q_1 q_2| = |(+2)(-2)| = 4

. For

QR_2

and

P_2S

,

|q_1 q_2| = 2

. For

PR

,

|q_1 q_2| = 1

.

According to Coulomb's Law, higher ionic charges create substantially stronger electrostatic forces of attraction between ions in the solid lattice.

4

Relate lattice energy to the physical property of melting point

Higher lattice energy requires significantly more thermal energy to break the ionic bonds, making

QS

the compound with the highest melting point.

The melting point of an electrovalent compound increases as the strength of the lattice attraction increases.

Key Concept

Lattice energy dependence on ionic charge magnitude (Coulomb's Law in ionic crystals)

Question 8Question →

An electrovalent compound is insoluble in water when its lattice enthalpy is smaller in magnitude than the total hydration enthalpy of its constituent gaseous ions.

True

False

Show answer & explanation

Answer: False

Answer

False. An electrovalent compound is soluble in water when the magnitude of its hydration enthalpy exceeds its lattice enthalpy, allowing ion-water electrostatic attractions to overcome ionic crystal lattice forces.

The statement is false because for an electrovalent compound to dissolve in water, the hydration energy released when ions interact with water molecules must overcome the lattice energy holding the crystal together. If hydration enthalpy is greater in magnitude than lattice enthalpy, the compound is soluble rather than insoluble.

Step-by-Step Solution

1

Identify the enthalpy changes during the dissolution of an ionic solid.

Dissolution depends on two key thermodynamic quantities: lattice enthalpy (energy required to separate solid ions into gaseous ions) and hydration enthalpy (energy released when gaseous ions are solvated by water).

The overall enthalpy of solution is approximated by

\Delta H_{\text{solution}} = \Delta H_{\text{lattice}} + \Delta H_{\text{hydration}}

.

2

Evaluate the condition where

|\Delta H_{\text{lattice}}| < |\Delta H_{\text{hydration}}|

.

The energy released during ion hydration is greater than the energy required to break the ionic lattice.

This leads to an exothermic dissolution process (

\Delta H_{\text{solution}} < 0

), which strongly favors the compound dissolving in water.

3

Determine the truth value of the statement.

The statement asserts that such a compound is insoluble, which contradicts chemical thermodynamic principles.

Therefore, the given statement is false.

Key Concept

Lattice Enthalpy vs Hydration Enthalpy in Ionic Compound Solubility

Question 9Question →

An element $M$ has the ground-state electronic configuration $1s^2 2s^2 2p^6 3s^2$ , while element $X$ has the configuration $1s^2 2s^2 2p^5$ . What is the chemical formula of the compound formed between $M$ and $X$ , and what type of bonding holds the compound together?

MX_2

; electrovalent (ionic) bonding

MX

; electrovalent (ionic) bonding

M_2X

; covalent bonding

MX_2

; covalent bonding

Show answer & explanation

Answer: $MX_2$ ; electrovalent (ionic) bonding

Answer

The correct compound formula is

MX_2

and the bonding is electrovalent (ionic).

The correct answer states that the compound formula is

MX_2

formed by electrovalent (ionic) bonding. Element

M

has 2 valence electrons (

3s^2

) which it transfers to two atoms of element

X

(each having 7 valence electrons,

2s^2 2p^5

), forming

M^{2+}

and two

X^-

ions. Bonding via complete electron transfer between metal and non-metal is electrovalent.

Step-by-Step Solution

1

Analyze the electronic configuration of element

M

to determine its valency and ion charge.

Element

M

(

1s^2 2s^2 2p^6 3s^2

) has 2 valence electrons in its outermost shell (

3s

). It donates 2 electrons to achieve a stable octet, forming the cation

M^{2+}

.

Elements with 1 or 2 outer electrons readily lose them to achieve stable noble gas electron configurations.

2

Analyze the electronic configuration of element

X

to determine its valency and ion charge.

Element

X

(

1s^2 2s^2 2p^5

) has 7 valence electrons in its outermost shell (

2s^2 2p^5

). It accepts 1 electron to complete its octet, forming the anion

X^-

.

Non-metals with 7 valence electrons require 1 additional electron for octet stability.

3

Balance the ionic charges to establish the formula unit and identify the bond type.

To maintain electrical neutrality, one

M^{2+}

ion combines with two

X^-

ions, resulting in the chemical formula

MX_2

. The complete transfer of electrons from a metal to a non-metal yields electrostatic attraction, which constitutes electrovalent (ionic) bonding.

Ionic compounds must be electrically neutral, and bonding formed by complete electron transfer is electrovalent.

Key Concept

Ionic (Electrovalent) Bond Formation and Formula Determination

Question 10Question →

Ionic compounds are generally brittle because applying a mechanical stress causes layers of ions to shift, bringing ions of identical charge into alignment and causing strong electrostatic repulsion.

True

False

Show answer & explanation

Answer: True

Answer

True. Applying mechanical stress causes layers of an ionic lattice to shift, bringing like-charged ions into direct alignment; the immediate electrostatic repulsion forces the crystal planes apart, rendering ionic solids brittle.

The statement is true because mechanical stress displaces adjacent rows in an ionic lattice, shifting like-charged ions into alignment. The powerful electrostatic repulsion generated between identical charges forces the crystal layers apart, causing the ionic solid to shatter.

Step-by-Step Solution

1

Identify the arrangement of particles in a solid ionic lattice.

An ionic crystal consists of alternating positive cations and negative anions organized in a regular three-dimensional array held by electrostatic attraction.

Determining the initial alternating charge pattern is necessary to understand how movement alters interionic forces.

2

Analyze the structural shift caused by an applied mechanical force.

The force causes one layer of ions to slide past another by one atomic position.

Mechanical impact displaces crystal planes relative to each other.

3

Evaluate the net electrostatic forces after displacement.

Ions of identical charge (

+

and

+

, or

-

and

-

) are brought into direct alignment, creating powerful repulsive forces that shatter the lattice along cleavage planes.

Electrostatic repulsion between like charges overcomes binding attraction, explaining the characteristic brittleness of ionic solids.

Key Concept

Brittleness and Mechanical Cleavage of Ionic Lattice Structures

Question 11Question →

Match each physical property or characteristic of ionic (electrovalent) bonding on the left with its correct microscopic or structural explanation on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

High melting and boiling points match with the need for extensive thermal energy to disrupt the giant 3D lattice; Electrical conductivity in molten/aqueous state matches with lattice destruction freeing mobile charge carriers; Solubility in water matches with hydration energy overcoming lattice energy; Non-directional nature matches with the electrostatic field acting uniformly in all directions.

Each property of ionic compounds directly stems from its underlying electrostatic structure: High melting points are caused by the strong 3D electrostatic attractions requiring high thermal energy to break; Electrical conductivity in molten/dissolved states occurs because ions are set free as mobile charge carriers; Solubility in water occurs when hydration energy exceeds lattice energy; Non-directionality arises because an ion's electrostatic field attracts opposite charges equally in all spatial directions.

Step-by-Step Solution

1

Analyze the high melting/boiling points of ionic compounds.

Recognize that ions are held in a giant lattice by strong electrostatic forces in all dimensions, requiring high heat energy to overcome.

Relates macro property (melting point) to micro structure (lattice binding energy).

2

Examine the electrical conduction mechanism in ionic substances.

In solid state, ions are fixed in lattice positions. Melting or dissolving releases these ions as mobile charge carriers.

Conduction requires free charge carriers, which are absent in solid ionic crystals.

3

Evaluate the dissolution of ionic compounds in polar solvents.

Polar water molecules surround separated ions (solvation/hydration), releasing energy that overcomes the lattice energy holding the crystal together.

Solubility depends on the thermodynamic balance between hydration enthalpy and lattice enthalpy.

4

Assess the directional nature of ionic bonding.

Because electrostatic attraction operates spherically in space, ionic bonds have no preferred angle or directional vector.

Charges attract equally in all directions, unlike localized shared electron pairs in covalent bonds.

Key Concept

Physical Properties and Structural Basis of Electrovalent (Ionic) Bonding

Ionic (Electrovalent) Bonding and Properties of Ionic Compounds

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