Allotropes%20of%20Carbon

1
Allotropes of Carbon

• Topic 4.2

2
Covalent Crystalline Solids

• There are substances which have a crystalline
  structure in which all the atoms are linked
  together by covalent bonds. Effectively, the
  crystal is a single molecule with a regular
  repeating pattern of covalent bonds, so is often
  referred to as a giant molecular structure or a
  macromolecule.

3
Allotropes of Carbon

• Allotropes are different forms of an element in
  the same physical state.
• Carbon has three allotropes graphite, diamond,
  and fullerene.
• Different bonding within these structures give
  rise to distinct forms with different properties

4
Graphite

• In graphite, each carbon atom is covalently
  bonded to 3 others, forming hexagons in parallel
  layers with bond angles of 120o.
• The layers are held only by weak van der Waals
  forces, so they can slide over each other.

5
Graphite
6
Graphite

• Density 2.26 g cm-3
• Contains one non-bonded, delocalized electron per
  atom, so it conducts electricity
• Non-lustrous, grey solid
• Used as a lubricant and in pencils

7
Diamond

• Each carbon atom is covalently bonded to 4
  others, tetrahedrally arranged in a regular
  repeating pattern with bond angles of 109.5o.
• It is the hardest known natural substance

8
Diamond
9
Diamond

• Density 3.51 g cm-3
• All electrons are bonded non conductor of
  electricity
• Lustrous crystal
• Polished for jewellery and ornamentation used in
  tools and machinery for grinding and cutting
  glass.

10
Fullerene (C60)

• Each carbon atom is bonded in a sphere of 60
  carbon atoms, consisting of 12 pentagons and 20
  hexagons.
• The structure is a closed spherical cage in which
  each carbon is bonded to 3 others

11
Fullerene
12
Fullerene

• Density 1.72 g cm-3
• Easily accepts electrons to form ions
• Yellow crystalline solid
• Reacts with K to make superconducting crystalline
  material related forms are used to make
  nanotubes for the electronics industry, catalysts
  and lubricants.

13
Silicon and Silicon Dioxide

• Like carbon, silicon is a Group 4 element and so
  its atoms have four valence shell electrons. In
  the elemental state, each silicon atom is
  covalently bonded to four others ina tetrahedral
  arrangement. This results in a giant lattice
  structure much like a diamond

14
Silicon Dioxide

• SiO2, commonly known as silica or quartz, also
  forms a giant covalent structure. This is
  structure is also a tetrahedrally bonded
  structure with bonds between Si and O atoms. Each
  Si atom is covalently bonded to four oxygen atoms
  and each O to two Si Atoms

15
Silicon Dioxide

• Note the formula is SiO2 and refers to the ratio
  of atoms within the giant molecule the actual
  number of atoms present will be a very large
  multiple of this.
• The structure is strong, insoluble in water, has
  a high melting point, and does not conduct
  electricity or heat.
• These are all properties associated with glass
  and sand different forms of silica.