1. Macromolecules (Network Covalent) Last part of Topic 4.3

2. 2 characteristics – some elements from group 14 (carbon and silicon form giant macromolecules the entire piece is one molecule – insoluble in almost all solvents

3. Carbon allotropes the same element can be covalently bonded in four of different forms (allotropes) – covalent network solids- atoms are held together by covalent bonds in a 3-D lattice structure that “go on forever” 1.graphite 2.graphene 3.diamond – molecular and have a definite formula 4.fullerenes

4. Graphene- The super material! strongly bonded carbon in a trigonal planar structure (120°) one of the thinnest and strongest known materials – only one atom thick, a two dimensional crystal superb conductor of electricity can be rolled up to form a carbon nanotube or folded into a sphere (fullerene)

6. Graphite multiple layers of graphene between the layers are weak bonds (called London forces) – electricity can easily move between the sheets since it has freely moving charged particles (electrons) – layers can slide past one another therefore a good lubricant – brittle and high melting point

9. Fullerenes has some delocalized (moving) electrons but cannot conduct electricity since electrons can’t move from one molecule to the next most famous is the C 60 fullerene often referred to as buckeyballs – 60 carbons in 12 pentagons and 20 hexagons can form a hollow, cage-like structure or tubes

10. Diamond repeating tetrahedral structure (109.5°) one of the hardest materials known very high melting point no free moving electrons since they are being shared in covalent bonds – cannot conduct electricity

11. see all the tetrahedrals put together

13. Silicon and silicon dioxide both (Si and SiO 2 ) are very “strong” structures very high melting point very high boiling point – silicon giant (macro) molecules made up of tetrahedrals covalently bonded together this structure is repeated over and over

14. silicon is in group 14 just like carbon, so notice the same covalent network solid shape

15. – silicon dioxide (sand) same structure as silicon but each silicon atom is bridged to its neighbors by an oxygen atom most common crystalline form is quartz high melting and boiling point does not conduct electricity