Magnesium oxide (MgO) has a significantly higher melting point than sodium chloride (NaCl)… — JAMB UTME

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 $Cl^-$ ).

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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.

Adım Adım Çözüm

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.

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.

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.

Anahtar Kavram

Lattice Energy and Ion Charge Dependency in Ionic Compounds

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