Question

Consider the following six solid binary oxides: CaO, Al2O3, PbO, Cs2O, SiO2, and Sb2O3. The pair(s) of ionic oxides is(are)

• A. CaO and Al2O3
• B. CaO and PbO
• C. Cs2O and Al2O3
• D. SiO2 and Sb2O3

Hint:

Ionic oxides are typically formed by metals with high electropositivity, such as alkali and alkaline earth metals.

Answer 1

The Correct Option is A, C

Determining ionic vs covalent character:

Ionic oxides form between:

• Highly electropositive metals (low electronegativity)
• Oxygen (high electronegativity)
• Large electronegativity difference (typically > 1.7)

Analyzing each oxide:

CaO:

• Ca²⁺ and O²⁻ ions
• Ca is an alkaline earth metal (Group 2)
• Large electronegativity difference
• Ionic 

Al₂O₃:

• Al³⁺ and O²⁻ ions
• Aluminum has moderate electronegativity
• Shows significant ionic character, though some covalent character exists
• Generally classified as ionic 

PbO:

• Pb²⁺ and O²⁻
• Lead is a post-transition metal with high polarizability
• Shows significant covalent character due to inert pair effect
• Predominantly covalent with some ionic character 

Cs₂O:

• Cs⁺ and O²⁻ ions
• Cesium is the most electropositive alkali metal (Group 1)
• Very large electronegativity difference
• Highly ionic 

SiO₂:

• Silicon-oxygen network structure
• Large covalent character (Si-O bonds)
• Covalent 

Sb₂O₃:

• Antimony oxide
• Antimony is a metalloid
• Shows significant covalent character
• Predominantly covalent 

Identifying ionic pairs:

(A) CaO and Al₂O₃ - Both ionic 

(B) CaO and PbO - CaO ionic, PbO has significant covalent character 

(C) Cs₂O and Al₂O₃ - Both ionic 

(D) SiO₂ and Sb₂O₃ - Both predominantly covalent

Answer: (A) and (C)