Chemical Bonding is one of the most important fundamental topics in O-Level Chemistry (and other equivalent Basic Chemistry syllabus). It is linked to many other topics in Chemistry. However, many students are not aware of it and take them very lightly.
Let’s check out a question that was emailed to me by one of the student that read this blog.
Hi
I just want to clarify whether the explanation is correct.
Q) Explain why graphite has a lower melting point than diamond. (1 mark).
The answer is “Graphite has fewer covalent bonds than Diamond.”
What about this answer:
“Graphite has weak van der wals forces between the layers. Lesser energy is required to overcome such forces. As a result, it has a lower melting point than diamond”.
Is this answer acceptable?
From my own understanding, diamond has 4 covalent bonds between the carbon atoms while graphite has 3 covalent bonds between the carbon atoms and weak van der wals forces. More energy is required to break the extra covalent bond in diamond than the weak van der wals forces between the layers of atoms in graphite.
Regards
Weijie
The suggested answer “Graphite has fewer covalent bonds than Diamond.” is INCORRECT and is one of the common mistakes made by students batch after batch every year. Not sure where he found this suggested answer though.
Weijie is correct in his own suggested answer. =)
Graphite? are made up of layers of hexagonal rings that are held together by weak intermolecular? van der Waals’ forces of attraction. Lesser energy is required to overcome such weak forces. As a result, it has a lower melting point than diamond which is made of carbon atoms that are covalently bonded strongly together to form an extensive 3-D network with tetrahedral arrrangement. A large amount of energy is required to break these strong covalent bonds.
Tips:
Covalent Bonds (an intramolecular bond) is much stronger than van der Waals’ forces (an intermolecular bond)
Remember to master this topic on Chemical Bonding if you want to excel in Chemistry. : )
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- O Level Chemistry Question: Chemical Bonding & Structural Properties
- O Level Chemistry: Which has lower Melting Point
- O Level Chemistry: Intro to Organic Chemistry – Part 1
May polymerisation appear this year?If yes what possible types of questions may come?
i have to say that it is wrong. Breaking the weak van der waals’ forces will only make the graphite smaller. Cause the layers can slide over and break easily. This does not change the state. It only changes the size. In order for the state to change, the covalent bonding must be overcame. As a result, it is correct that graphite has less covalent bonding than diamond so diamond has higher melting point. My school taught me like this and i did wrote on my exam, graphite has weak van der waals, i got a straight zero