2.2.7 - Covalent Network Structures
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What are covalent network structures?
crystalline lattice in which atoms are linked together by covalent bonds
What are examples of allotropes of carbon?
diamond, graphite, graphene, C60 fullerene
What is an allotrope?
molecules with different bonding/structural patterns/chemical/ physical properties of the same element and the same state
What is the structure of diamond?
each C is sp3 hybridized, covalently bonded to 4 others, tetrahedral
What is the structure of graphite?
each C is sp2 hybridized, covalently bonded to 3 others, hexagons, 120 bond angles, remaining valence electrons are delocalized, layers held only by London Dispersion forces
What is the structure of graphene?
each C is sp2 hybridized, covalently bonded to 3 others, hexagons, 120 bond angles, single layer, remaining electrons are delocalized
What is the structure of C60 fullerene?
each C is sp2 hybridized, bonded in sphere of 60 C, pentagons + hexagons, each C bonded to 3 others, not giant, fixed formula
Which allotropes of C can conduct electricity and why?
graphite b/c one non-bonded delocalized electron per atom, graphene b/c one delocalized electron per atom, C60 fullerene (poor) b/c little electron movement between molecules
Which allotropes of carbon do not conduct electricity and why?
diamond b/c all electrons are bonded so non-mobile
Which allotropes of C are good conductors of thermal energy?
diamond, graphene
Which allotropes of C are poor conductors of thermal energy?
graphite unless heat can be forced to conduct in parallel direction to crystal layers, C60 fullerene
What are some physical/chemical properties of diamond?
hard, brittle, high melting point
What are some physical/chemical properties of graphite?
soft, slippery due to slippage of layers, brittle, high melting point, most stable allotropes of C
what are some physical/chemical properties of graphene?
thinnest material to exist, strongest, flexible, high melting point
What are some physical/chemical properties of C60 fullerene?
light, strong, reacts with K to make super-conducting crystalline material, low melting point
In the elemental state, what can Si be covalently bonded to O to resemble?
giant lattice structure like diamond
What are some structural properties of silicon dioxide?
strong, insoluble in water, high melting point, non-conductor of electricity
Why does C have a higher tendancy to bond with other C atoms while Si has a higher tendancy to bond with O?
due to greater strength of C-C bonds compared to Si-Si bonds, C has smaller atomic radius resulting in greater electrostatic attraction between nuclei and shared pairs of electrons