2. Ionic Crystals The large difference in electronegativity between metal and nonmetal atoms results in the transfer of electrons. The result is the formation of cations and anions, which are attracted to each other through an ionic bond. This results in a crystal lattice structure, in which the each ion is surrounded by ions of the opposite charge. This is a very stable arrangement.

3. Metallic Crystals Valence electrons are not held strongly by individual atoms, but act as freely-moving, negative “glue” that holds the positive ions together.

4. Molecular Crystals Most nonmetal elements and molecular compounds are not solid at room temperature. iodine carbon dioxide “dry ice” Individual molecules are held together by relatively weak intermolecular forces (London, dipole-dipole hydrogen bonding).

5. Covalent Network Crystals Covalent network crystals are usually much harder and have much higher boiling and melting points than ionic crystals. variations of quartz amethyst rose quartz citrine

6. diamond Diamond’s structure is an example of a convalent network, where individual carbon atoms are held together by covalent bonds. The cumulative effect of these bonds is extremely strong, explaining the hardness and high melting points of these structures. diamondgraphitebuckyballcarbon nanotube Carbon can form many different types of covalent networks, each with unique physical properties.

7. Semiconductors In an atom of a semiconductor, the highest energy levels may be thought of as being full of electrons that are unable to move from atom to atom. In semiconductor, electrons require only a small amount of energy to jump to the next higher energy level, which is empty. Once in this level, they may move to another atom easily.

9. Read pgs. 119 – 127 pgs. 122, 123, 128 Practice #’s 2 – 19 pgs. 129 – 130 Section 3.5 Questions #’s 1 – 9