CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Three crystalline substances—labeled X, Y, and Z—are tested in the laboratory. Their physical properties are summarized below.
Property
Substance X
Substance Y
Substance Z
Melting point / °C
801
113
3550
Electrical conductivity when molten
High
Negligible
Negligible
Solubility in water (25 °C)
High
High
Insoluble
Each substance is composed solely of the elements shown in the table, along with their Pauling electronegativity values.
Element
Electronegativity
Na
0.9
Cl
3.0
C
2.5
O
3.5
Si
1.8
Assume that:
• Substance X has empirical formula NaCl.
• Substance Y has empirical formula C₂O.
• Substance Z has empirical formula SiC.
(a) For the primary chemical bond in each empirical formula, compute ΔEN using the values provided.
(b) For each substance, identify the predominant type of bonding (ionic, covalent network, or molecular covalent) and justify your choice using BOTH your ΔEN calculations and the physical‐property data in the first table.
(c) Among the three substances, determine which exhibits the greatest percent ionic character in its primary bond. Support your answer with a coherent argument that integrates numerical electronegativity differences and at least one macroscopic property.