Ionic crystals such as sodium chloride are hard and have high melting points because
Correct answer: B. strong electrostatic forces act between oppositely charged ions throughout the lattice
- A. their ions are held by weak van der Waals forces
- B. strong electrostatic forces act between oppositely charged ions throughout the lattice
- C. they contain covalent bonds between the ions
- D. the ions are free to move at room temperature
Explanation
Every ion attracts all the oppositely charged ions around it, and a great deal of energy is needed to break this extended three dimensional network, so the melting point of sodium chloride is 801 degrees Celsius. The ions are locked in place in the solid, which is why solid sodium chloride does not conduct electricity while the molten salt and its solution do.
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About Ionic and Molecular Crystals
Ionic crystals contain oppositely charged ions held by electrostatic forces, whereas molecular crystals contain discrete molecules joined by weaker intermolecular forces. Their structures explain differences in melting point, hardness, volatility, solubility and electrical conductivity, especially between solid and molten states.
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