2.8 - Giant Covalent Structures

• allotropes


  different forms of the same element in the same physical state
• allotropes of carbon


  diamond

  graphite

  graphere

  fullerenes
• bonding & structure of allotropes of carbon

  strong covalent bonds

  most form giant covalent structures
• giant covalent structures


  covalent bonds can lead to huge lattices

  electrostatic attractions holding atoms together is much stronger than electrostatic attractions between simple covalent structures
• properties of giant covalent structures

  high melting points and are hard due to very strong covalent bonds throughout lattice arrangement

  good thermal conductors because vibrations travel easily through stiff lattices

  insoluble because atoms are more attracted to each other than solvent molecules due to covalent bands (proves it has no ions)

  can't conduct electricity due to no changed ions or delocalised electrons
• structure of diamond

  giant covalent structure

  each carbon atom forms 4 covalent bonds with other carbon atoms in a tetrahedral arrangement
• physical properties of diamond

  very high sublimation point due to very strong covalent bonds

  very hard due to covalent bonds

  doesn't conduct electricity due to no delocalised electrons

  insoluble in water because carbons are more attracted to each other than to solvent

  good thermal conductor
• uses of diamond

  jewellery

  glass cutters & diamond studded saws because it's very hard & a good thermal conductor so doesn't overheat
• structure of graphite


  giant covalent structure

  layered

  each carbon atom forms 3 covalent bounds with other carbons so there's a delocalised electron

  hexagonal arrangement within layer

  delocalised electrons had to large temporary dipoles induce opposite dipoles in sheets above & below so sheets are joined together
• physical properties of graphite

  high melting point due to strong covalent bonds

  soft & slippery because bond between layers is weak so they can slide over one another

  lower density than diamond due to spaces between layers

  high sublimation temperature due to giant structure & covalent bonds

  insoluble in water & organic solvents because carbon atoms are too strongly attracted to each other

  conducts electricity because there are delocalised elections
• uses of graphite


  make crucibles for molten metals as it can withstand high temperature

  used in many composites to strengthen them

  used as lubricant because it's soft & greasy
• structure of graphene


  single layer of graphite

  2D

  giant covalent structure

  each carbon is covalently bonded to 3 other carbons so there are delocalised electrons
• properties of graphene


  conducts electricity due to delocalised electrons

  transparent

  flexible

  Strong

  thin

  lightweight
• uses of graphene


  aircrafts & cars

  used in composites, touchscreens in phonce
• structure of silicon dioxide - SiO2

  like diamond but with silicon & Oxygen

  giant Covalent structures
• properties of silicon dioxide

  high melting point due to strong silicon-oxygen covalent bonds

  hand due to strong covalent bonds

  doesn't conduct electricity due to no delocalised electrons

  insoluble in ulater due to very strong attractions between silicon & oxygen
• structure of fullerenes


  molecular form of carbon

  carbon forms 3 covalent bonds with other carbons so there's one delocalised electron

  spherical
• buckminster fullerene


  C60

  black solid
• properties of fullerenes


  soluble in various solvents

  electrical insulator because delocalised electrons can't more between molecules
• uses of fullerenes/nanotubes


  Strengthen golf clubs, fishing rods

  medicine

  Mascara & printing ink as it's soluble
• reaction of fullerenes with groups 1 & 2 metals

  form superconducting systems at very lour temperatures

  reaction produces a rare type of salt where electrons transferred to C60 move around whole salt like in a metal

  3Rb + C60 → (Rb+)3C603-