Giant covalent substances

Question 1

what do giant covalent compounds have high melting and boiling points? (2)

Answer 1

-covalent bonds are strong
-a lot of energy is needed to break up these large structures during melting and boiling.

Question 2

why can giant covalent compounds not conduct electricity? and what is an exception?

Answer 2

-have no overall charge, so most cannot conduct electricity
-graphite

Question 3

why are giant covalent compounds insoluble in water?

Answer 3

cannot form these strong attractions with water, so they are insoluble.

Question 4

describe the structure and bonding of diamonds: (3)
what is each carbon atom joined to?
what structure do they form?
do they have delocalised electrons?

Answer 4

-four other carbon atoms by covalent bonds
- regular tetrahedral network structure
-no free electrons

Question 5

properties and uses of diamonds: (2)

Answer 5

-rigid network of carbon atoms, held together by strong covalent bonds, makes diamond very hard.
-useful for cutting tools or drilling equipment (such as diamond-tipped glass cutters and oil rig drills)

Question 6

describe the structure and bonding of graphite: (4)
what is each carbon atom joined to?
what structure do they form?
what is between the layers?
do they have delocalised electrons?

Answer 6

-three other carbon atoms by covalent bonds
-hexagonal layered network structure
-have weak forces between layers and can slide over each other
- one un-bonded outer electron (delocalised, and are free to move)

Question 7

properties and uses of graphite: (4)

Answer 7

-delocalised electrons are free to move through the structure of graphite, so graphite can conduct electricity.
-useful for electrodes in batteries and for electrolysis.

-layers in graphite can slide over each other because the forces between them are weak.
-makes graphite slippery, so it is useful as a lubricant.

Question 8

describe the structure of graphene: (3)

Answer 8

-single layer of graphite
-joined to 3 other carbon atoms

Question 9

what is the melting point of graphene like? and why?

Answer 9

-a very high melting point
-is very strong because of its large lattice of carbon atoms joined by covalent bonds

Question 10

can graphene conduct electricity?

Answer 10

yes as it has delocalised electrons that are free to move across its surface

Question 11

what is fullerene?
what are two examples of fullerenes?

Answer 11

-molecular form of the element carbon.
-nanotubes and buckminsterfullerene.

Question 12

what do nanotubes resemble?

Answer 12

a layer of graphene rolled into a tube shape

Question 13

properties of nanotubes: (3)

Answer 13

-strong
-high tensile strength, so they are strong in tension and resist being stretched.
-conduct electricity (because they have delocalised electrons)

Question 14

what do buckminsterfullerene resemble?

Answer 14

spheres or squashed spheres of carbon atoms.

Question 15

why are buckminsterfullerenes not classed as giant covalent networks?

Answer 15

-they are made up of large molecules

Question 16

why does buckminsterfullerene have a low melting (NOT BOILING) point?
what does this result in? (3)

Answer 16

-weak intermolecular forces exist between buckyballs.
require little energy to overcome,

-substances consisting of buckyballs are slippery and have lower melting points than graphite or diamond.

Question 17

how many carbon atoms does Buckminsterfullerene consist of?

Answer 17

60

Question 18

what do simple polymers consist of?

Answer 18

large molecules that contain chains of carbon atoms of no set size