02 Microscopic World I

• In simple molecular structure, weak van der Waals' forces exist between molecules.
• In simple molecular structure, strong covalent bonds exists between atoms within a molecule.
• Simple molecular structure under room conditions are gases, volatile liquids, or solids with low melting points.
• Simple molecular structure have low melting and boiling points because molecules are held together only by weak van der Waals' forces. Little energy is required to break these bonds.
• Simple molecular structure is soft as it is easy to separate molecules.
• Simple molecular structures are insoluble in aqueous solvents as the weak attractive forces between the molecules cannot overcome the strong attractive forces between the water molecules.
• Simple molecular structures are soluble in non-aqueous solvents as they can overcome the weak attractive forces in it.
• Giant covalent structure has high melting and boiling points are more energy is required to break the strong covalent bond between atoms.
• Giant covalent structure is hard as atoms cannot slide over one another, except graphite. In graphite, only weak van der Waals' forces exist between layers.
• Giant covalent structures are insoluble in any solvent as it is difficult to separate atoms that are held together by strong covalent bonds.
• Giant covalent structures do not conduct electricity as all outermost shell electrons are held firmly in covalent bonds and there are no delocalized electrons. Except graphite, as one outer electron of each carbon atom is delocalized.
• Giant ionic structures are crystalline in solid state.
• Giant ionic structures have high melting and boiling points as more energy is required to break the strong ionic bond.
• Giant ionic structures are brittle. When under stress, the movement of ions bring ions of the same charge close to each other, which will cause repulsion.
• Giant ionic structures are soluble in aqueous solvents. Attraction exists between ions and water molecules and the water molecules surround the ions. The ions are hydrated.
• Giant ionic structures are insoluble in non-aqueous solvents.
• Giant ionic structures conduct electricity when molten or dissolved in aqueous solvents because they are electrolytes. The ions become mobile.
• Giant metallic structures have high melting and boiling points as more energy is required to break the strong metallic bond.
• Giant metallic structures have high density as metal ions are closely packed.
• Giant metallic structures are malleable and ductile as metallic bonds are non-directional, they continue to hold the metal ions together. The layers of metal ions can slide over one another.
• Giant metallic structures are good conductors of electricity as they have delocalized electrons.
• Giant metallic structures are good conductors of heat as heat is transferred by collisions of electrons.