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Ionic Bonding & Lattice Energy Questions

Home Chemistry Ionic Bonding & Lattice Energy
Q. An ionic bond is formed by:
Delocalization of electrons in a metal lattice
Electrostatic attraction between oppositely charged ions
Sharing of electron pairs between atoms
Overlap of atomic orbitals

Explanation:

Ionic bonds result from the electrostatic attraction between oppositely charged ions formed when one atom transfers electrons to another.

Q. Which of the following pairs is most likely to form an ionic compound?
Nitrogen and nitrogen
Carbon and oxygen
Hydrogen and chlorine
Potassium and chlorine

Explanation:

Ionic bonds form between metals with low ionization energy and nonmetals with high electron affinity. K (alkali metal) and Cl (halogen) form KCl, a classic ionic compound.

Q. Lattice energy is defined as:
The energy released when an electron is added to an atom
The energy required to melt an ionic solid
The energy required to remove an electron from an atom
The energy released when gaseous ions form one mole of an ionic solid

Explanation:

Lattice energy is the energy released when one mole of an ionic solid forms from its gaseous ions, or equivalently the energy needed to separate one mole of the solid into gaseous ions.

Q. Lattice energy increases with:
Lower ionic charges only
Lower ionic charges and larger ionic radii
Higher ionic charges and smaller ionic radii
Larger ionic radii only

Explanation:

According to Coulomb's law, lattice energy is proportional to the product of the ionic charges (q1·q2) divided by the interionic distance (r). Higher charges and smaller radii both increase lattice energy.

Q. Which compound has the highest lattice energy?
MgO
NaF
NaCl
KCl

Explanation:

MgO has Mg²⁺ and O²⁻ ions with high charges and small radii, giving it a much larger lattice energy than compounds with +1/−1 charges such as NaCl, KCl, or NaF.

Q. Which of the following ionic compounds would be expected to have the highest melting point?
KBr
NaCl
NaI
MgO

Explanation:

Higher lattice energy correlates with higher melting points. MgO (2+/2− charges, small radii) has the highest lattice energy among the given options, so it melts at the highest temperature.

Q. The Born-Haber cycle is used to determine:
The rate of an ionic reaction
The pH of a solution
The activation energy of a reaction
The lattice energy of an ionic compound

Explanation:

The Born-Haber cycle applies Hess's law to calculate the lattice energy of an ionic compound from measurable quantities: sublimation, ionization, dissociation, electron affinity, and formation enthalpy.

Q. Which of the following is a property characteristic of ionic compounds?
They conduct electricity in the solid state
They are typically gases at room temperature
They have low melting points
They conduct electricity in the molten or aqueous state

Explanation:

Ionic compounds conduct electricity when molten or dissolved (because ions are free to move), but not in the solid state (where ions are locked in the lattice).

Q. Ionic compounds typically dissolve in water because:
Water reacts chemically with the ions
Water's high polarity stabilizes the ions, overcoming lattice energy
Water is a strong acid
Water is non-polar

Explanation:

Water is a polar solvent with a high dielectric constant. Its partial charges stabilize both cations (via oxygen lone pairs) and anions (via hydrogen atoms), and the ion-dipole interactions overcome lattice energy.

Q. The energy required to remove an electron from a gaseous atom is called:
Bond dissociation energy
Lattice energy
Electron affinity
Ionization energy

Explanation:

Ionization energy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom.

Q. The energy released when an electron is added to a gaseous atom is called:
Lattice energy
Electron affinity
Ionization energy
Electronegativity

Explanation:

Electron affinity is the energy change (usually negative/released) when an electron is added to a neutral gaseous atom.

Q. The Born equation predicts that hydration enthalpy is proportional to:
z/r² (charge divided by radius squared)
z·r (charge times radius)
z²/r (charge squared divided by radius)
r/z (radius divided by charge)

Explanation:

The Born equation gives ΔG_hydration ∝ -z²/r, where z is the ion charge and r its radius. Smaller, highly charged ions are more strongly hydrated.

Q. Which of the following ions has the smallest ionic radius?
O²⁻
Na⁺
Al³⁺
F⁻

Explanation:

Isoelectronic ions: N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺, Al³⁺ all have 10 electrons. Higher positive charge pulls the electron cloud closer, so Al³⁺ has the smallest ionic radius.

Q. Which is the correct formula for the ionic compound formed from calcium and nitride ions?
Ca₃N₂
CaN
Ca₂N₃
Ca₃N

Explanation:

Ca forms Ca²⁺ and nitride is N³⁻. Charge balance requires 3 Ca²⁺ and 2 N³⁻ to give neutrality: Ca₃N₂.

Q. Which of the following statements about ionic solids is FALSE?
They deform easily under mechanical stress
They are poor electrical conductors in the solid state
They are hard and brittle
They have high melting points

Explanation:

Ionic solids are typically hard and brittle, but they shatter (not deform) under stress because the ions are rigidly ordered. The claim that they deform easily is false.

Q. Which factor most strongly affects the solubility of an ionic compound in water?
Molecular mass only
Nature of the cation only
Balance between lattice energy and hydration energy
Crystal color

Explanation:

Solubility depends on the balance between the lattice energy (favoring the solid) and the hydration energies of the ions (favoring dissolution). When hydration dominates, the salt dissolves.

Q. Which of the following compounds is LEAST likely to exist as an ionic solid?
CCl₄
NaCl
KBr
MgO

Explanation:

Ionic character depends on electronegativity difference. CCl₄ is covalent (small ΔEN, nonpolar solvent-like properties). The others are predominantly ionic (metal + nonmetal).

Q. The strength of an ionic bond is inversely related to:
The dielectric constant of the medium
The atomic masses of the ions
The charges on the ions
The distance between the ions

Explanation:

According to Coulomb's law (F ∝ q₁·q₂/r²), force is inversely related to the square of the distance between ions. Larger ions produce weaker ionic bonds.

Q. An ionic bond is most likely formed between elements with:
Similar electronegativities
A large electronegativity difference
The same ionization energies
Identical electronegativities

Explanation:

Large electronegativity differences (typically >1.7) favor electron transfer from a metal (low electronegativity) to a nonmetal (high electronegativity), producing ions.

Q. Which ionic compound is expected to be the most soluble in water?
CaSO₄
SrSO₄
MgSO₄
BaSO₄

Explanation:

Solubility of alkaline earth sulfates decreases down the group (BeSO₄ > MgSO₄ > CaSO₄ > BaSO₄) because lattice energy decreases more slowly than hydration energy. MgSO₄ is much more soluble than BaSO₄.

Q. The lattice enthalpy of an ionic solid can be estimated using:
The van der Waals equation
The Henderson-Hasselbalch equation
The Nernst equation
The Kapustinskii or Born-Landé equation

Explanation:

The Kapustinskii equation (like the Born-Landé equation) estimates lattice enthalpy from charges and ionic radii. The Born-Landé and Kapustinskii equations are standard textbook methods.

Q. In the Born-Haber cycle for NaCl, which step requires energy input?
Formation of NaCl lattice
Ionization of Na and dissociation of Cl₂
Sublimation of Na only
Electron affinity of Cl

Explanation:

Removing an electron from Na (ionization energy) and dissociating Cl₂ require energy. Sublimation of Na and ionization of Na are endothermic; Cl₂ bond breaking is endothermic; Cl electron affinity and lattice formation are exothermic.

Q. Which of the following has the greatest ionic character?
HBr
KF
HI
HCl

Explanation:

Ionic character correlates with electronegativity difference. Among these, KF has the largest ΔEN (K 0.82, F 3.98 → ΔEN ≈ 3.16), making it the most ionic.

Q. Fajans' rules predict that a covalent bond is more likely when:
Both ions are large and singly charged
The cation is large and the anion is small
The cation is small and highly charged and the anion is large and polarizable
Both ions have the same electronegativity

Explanation:

Fajans' rules: high cation charge, small cation size, and large anion size all favor polarization of the anion by the cation, giving more covalent character. LiI satisfies all three.

Q. Which of the following pairs of ions would form the strongest ionic bond?
Al³⁺ and O²⁻
K⁺ and Br⁻
Na⁺ and Cl⁻
Cs⁺ and I⁻

Explanation:

Lattice energy ∝ (q₁q₂)/r. Al³⁺ and O²⁻ have the highest charges (3+/2−) and relatively small radii, so Al₂O₃ has exceptionally strong ionic bonding.

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