Difficulty: Easy
Correct Answer: form strong hydration shells via ion–dipole interactions around both positive and negative ions
Explanation:
Introduction / Context:
Solubility of ionic solids like NaCl in water is a cornerstone concept in general chemistry. Water’s polarity enables it to stabilize separated ions, overcoming lattice energy and allowing dissolution.
Given Data / Assumptions:
Concept / Approach:
The partial negative charge of oxygen in H2O orients toward cations; the partial positive charges on hydrogens orient toward anions. These ion–dipole interactions generate hydration shells that stabilize ions in solution. We often describe the ensemble as a solvation or hydration sphere.
Step-by-Step Solution:
Recognize polarity → water's dipole aligns with ions.
Form hydration shells → multiple water molecules coordinate around Na+ and Cl–.
Energy balance → hydration (solvation) energy compensates for lattice energy.
Result → crystal dissociates into solvated ions; salt dissolves.
Verification / Alternative check:
Conductivity measurements increase upon dissolution due to mobile ions; spectroscopic and simulation studies visualize hydration shells around ions.
Why Other Options Are Wrong:
Nonpolar covalent bonding (option B) does not occur; option C denies directed ion–dipole stabilization; option D suggests electron sharing to form covalent bonds, which is not the dissolution mechanism; exclusive hydrogen bonding to chloride (option E) is incomplete and misleading.
Common Pitfalls:
Calling these interactions “hydrogen bonds to ions”; the correct term is ion–dipole interactions, though water can hydrogen bond to other water molecules in the hydration shell.
Final Answer:
form strong hydration shells via ion–dipole interactions around both positive and negative ions.
Discussion & Comments