Structure And Physical Properties

Question 0

Network covalent crystals

Answer 0

Network covalent crystals have the strongest attraction holding atoms together. They have the highest melting points and are the hardest of all crystals.

Question 1

Physical properties are related to the forces between atoms and molecules in a crystal.

Answer 1

Hardness, melting point, and boiling point are all measures of the strength of interatomic or intermolecular attraction holding the crystal together. Stronger attraction results in lower vapor pressures.

Question 2

Ionic crystals

Answer 2

Ionic crystals have strong electrostatic forces holding atoms together. They tend to have high melting and boiling points, and are poor conductors in the solid phase (because the electrons are in fixed positions). However, when Ionic crystals are in the aqueous phase, they are good conductors because the charge is mobile.

Question 3

Nonpolar molecules

Answer 3

Nonpolar molecules, held together predominately by van der Waals forces, are soft crystals, art easily deformed, and vaporize easily. They have much lower melting and boiling point than polar compounds of similar molar mass. Nonpolar molecules are very poor conductors and tend to be more volatile because of their hive vapor pressure.

Question 4

Polar molecules

Answer 4

Polar molecules have intermolecular attractions that are weaker than ionic forces but are much stronger than nonpolar dispersion forces. The melting and boiling points of polar compounds depend on the strength of the dipole moment of the two compounds. The stronger the cumulative dipole moment, the greater the intermolecular attraction and the higher the melting and boiling points.