Giant molecular substances

Question 1

Describe the structure of a giant covalent substance

Answer 1

many atoms

joined by strong covalent bonds

arranged in a regular lattic structure

Question 2

What type of elements (metal/non metal) can they be?

Answer 2

non metal elements (e.g. carbon)

non metal compounds (silica)

Question 3

Describe the boiling/melting points

Answer 3

high

Question 4

What state are they in at room temperature?

Answer 4

solids

Question 5

Explain the boiling points and state at room temperature

Answer 5

there are many strong covalent bonds that must be broken for it to change state

this requires a lot of energy to be transferred

this results in boiling and melting points above room temp

Question 6

Are they soluble?

Answer 6

no

Question 7

Describe the structure of diamond and its properties

Answer 7

each carbon atom bonded to 4 others

strong covalent bonds between atoms

• rigid structure
• hardest natural material
• high melting point
• does not conduct electricity

Question 8

Explain 3 structural features of diamond

Answer 8

rigid/hard:

• each carbon bonded to 4 others
• comprised of many strong covalent bonds

high melting point:

• many strong covalent bonds to break to cause melting
• requires lots of energy

no electrical conductivity:
-no free/spare moving electrons to carry charge

Question 9

Describe the structure of graphite

Answer 9

each carbon atom bonded to 3 others

weak intermolecular forces between layers

strong covalent bonds between atoms in a layer

• layers of hexagonal rings
• high melting point
• conducts electricity
• soft and slippery

Question 10

Explain 3 structural features of graphite

Answer 10

slippery:

• attraction between layers is weak
• layers easily move/slide past each other

high melting point:

• many strong covalent bonds that need to be broken
• requires lots of energy

conducts electricity:

• there is one free electron per atom to carry electrical charge
• it is delocalised and is free to move between layers

Question 11

Graphite is used to make electrodes because it conducts electricity.

Explain why it conducts electricity but diamond does not.

Answer 11

a carbon atom can form 4 covalent bonds

in graphite, each carbon atom only forms 3 covalent bonds

this leaves the non-bonding outer electrons to become delocalised

they can move through the structure, allowing them to carry electrical charge, and causing graphite to conduct electricity

diamond has 4 bonds per carbon atom, so it has no free moving electrons to carry charge

Question 12

Compare and contrast the structure and bonding of diamond and graphite

Answer 12

• only contain carbon atoms
• atoms covalently bonded to each other
• lattice structure
• diamond has 4 covalent bonds per atom, graphite has 3
• diamond has no delocalised electrons, graphite does
• graphite has a layered structure (with weak attraction), diamond does not

Question 13

Explain, in terms of bonding and structure, why graphite is used as a lubricant

Answer 13

graphite has weak intermolecular/attractive forces between its layers, so the layers can slide over each other

this makes graphite soft/slippery