An element M forms a stable electrovalent chloride with the formula MCl_2. If the dipositi… — JAMB UTME

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.Answer
B
It conducts electricity in both the solid and molten states because delocalized valence electrons move freely through the ionic crystal lattice.
C
It has a low melting point and conducts electricity in the solid state because $M^{2+}$ cations migrate easily between lattice nodes.
D
It conducts electricity when molten because the neutral compound dissociates into free electrons and uncharged elemental atoms.

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

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.

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.

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

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