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Blue diamonds

Blue diamonds

Postby alics » Wed Oct 22, 2014 10:30 pm

Blue diamonds are an impure form of carbon. Part of the structure of a blue diamond is
shown below in (Figure # 1)
Blue diamonds have a high melting point and can conduct electricity.
(a) Explain, in terms of structure and bonding, why blue diamonds have a high melting
point.

(b) Normal diamonds are a pure form of carbon. They do not conduct electricity.
(i) Explain, in terms of structure and bonding, why normal diamonds do
not conduct electricity.

(ii) Suggest why blue diamonds can conduct electricity.

(c) Graphite is another pure form of carbon. Suggest
two reasons why graphite is often used as an electrode in electrolysis.
1 ................................................
2 ................................................
Attachments
Fig 1.jpg
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Re: Blue diamonds

Postby umercm » Wed Oct 22, 2014 11:24 pm

(a) Many (strong) covalent bonds
IGNORE: has a giant molecular structure
needs a lot of energy to break bonds / needs a lot of heat to break bonds / needs high temperature to break bonds
ALLOW: hard to break the bonds / large amount of energy to overcome bonds / lot of energy
needed to break strong forces between atoms
NOT: (just) lot of energy needed to break strong forces
REJECT: references to intermolecular or ionic forces = 0 for the question

(b) (i) no free electrons / no mobile electrons / electrons not free to move / all outer electrons
fixed in position / no delocalised electrons / all electrons involved in covalent bonding / no sea of electrons
ALLOW: the four electrons needed to form a covalent bond
IGNORE: no ions to move

(ii) (some) electrons free to move / it has delocalised electrons / blue diamond has
delocalised electrons (some of the) electrons are delocalised / (some) free electrons /
sea of electrons
IGNORE: boron is metallic / boron is a metalloid / boron has sea of electrons / boron has
delocalised electrons

(c) Any two from:
• conducts electricity / has free moving electrons
• high melting point
• (relatively) unreactive . ALLOW: less reactive / doesn’t react with solution
• doesn’t dissolve in water / insoluble in water . IGNORE: price / it is a solid
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