Thursday, September 29, 2005
CHEMISTRY: structure of macromolecules
DIAMOND and GRAPHITE
this is something like a continuation I guess. more in-depth (:
DIAMOND
1. tetrahedral structure
-each carbon atom is covalently bonded to 4 other carbon atoms
2. hard (due to covalent bonds)
3. high melting point (3550 degC) and boiling point (4827 degC)
-a lot of heat energy is required to break the covalent bonds
4. does not conduct electricity
-carbon has 4 valence electrons and since it is tetrahedral all 4 electrons are used in bonding, so there are no mobile charged particles
5. an allotrope of carbon
-different forms of the same element
USES OF DIAMOND
1. as tips of drills to drill through the ground/seabed (due to hardness)
2. grinding (hardness again)
3. polishing
GRAPHITE
1. made of flat layers of carbon atoms. layers have weak van der waal's forces between them. each carbon atom is covalently bonded to three others.
2. "soft” and slippery
- the layers have weak van der waal's forces between them, and slide off easily, giving the impression that it is soft.
3. high melting point (3652-3697 degC) and boiling point (4200 degC)
- covalent bonds between carbon atoms within each layer need a lot of heat energy to break
4. can conduct electricity
- unlike diamond each atom is bonded to three others so there is one extra delocalised electron that is free and mobile and thus graphite can conduct electricity because there are charged particles
5. an allotrope of carbon
- in fact, graphite is the stablest allotrope of carbon, even diamond will become graphite. you can like observe it (but WAIT LONG LONG!)
USES OF GRAPHITE
1. lubricant (soft and slippery to reduce friction, and can be used at high temperatures as well due to high MP and BP)
2. pencil lead (soft, layers slide off onto paper and stick there)
3. inert electrode for electrophoresis (good conductor of electricity)
this is something like a continuation I guess. more in-depth (:
DIAMOND
1. tetrahedral structure
-each carbon atom is covalently bonded to 4 other carbon atoms
2. hard (due to covalent bonds)
3. high melting point (3550 degC) and boiling point (4827 degC)
-a lot of heat energy is required to break the covalent bonds
4. does not conduct electricity
-carbon has 4 valence electrons and since it is tetrahedral all 4 electrons are used in bonding, so there are no mobile charged particles
5. an allotrope of carbon
-different forms of the same element
USES OF DIAMOND
1. as tips of drills to drill through the ground/seabed (due to hardness)
2. grinding (hardness again)
3. polishing
GRAPHITE
1. made of flat layers of carbon atoms. layers have weak van der waal's forces between them. each carbon atom is covalently bonded to three others.
2. "soft” and slippery
- the layers have weak van der waal's forces between them, and slide off easily, giving the impression that it is soft.
3. high melting point (3652-3697 degC) and boiling point (4200 degC)
- covalent bonds between carbon atoms within each layer need a lot of heat energy to break
4. can conduct electricity
- unlike diamond each atom is bonded to three others so there is one extra delocalised electron that is free and mobile and thus graphite can conduct electricity because there are charged particles
5. an allotrope of carbon
- in fact, graphite is the stablest allotrope of carbon, even diamond will become graphite. you can like observe it (but WAIT LONG LONG!)
USES OF GRAPHITE
1. lubricant (soft and slippery to reduce friction, and can be used at high temperatures as well due to high MP and BP)
2. pencil lead (soft, layers slide off onto paper and stick there)
3. inert electrode for electrophoresis (good conductor of electricity)
# we mugged! @ 6:30 AM 
