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Offline emilyjohnson

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help with chemisty!
« on: 06/02/2010 19:06:39 »
1.Diamond and graphite are both forms of carbon. Diamond is very hard. Graphite is soft and flaky. How could these different properties be exp?

1. They have different submicroscopic arrangments of the carbon atoms.
2.They must contain other elements
3.They have the same macroscopic properties
4.They have diff. compositions

2.which has the most mass?
1. 1 kg of cotton balls that fill a small pillow
2.a 1-kg lead cube, 4.44 cm per side
3.1 kg of water that fills a 1-liter bottle
4.they are all the same

3. Of the materials in question 2, which has the greatest density?
1.cotton balls
2.lead
3.water
4.they are all the same


 

Offline Geezer

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help with chemisty!
« Reply #1 on: 06/02/2010 22:26:12 »
These wouldn't happen to be homework questions by any chance?
 

Offline Spannerman

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help with chemisty!
« Reply #2 on: 23/02/2010 14:41:29 »
This does seem like homework :-).

Q1) The carbon in graphite is bonded to three other carbon atoms, whereas diamond has four bonds.
    Answer - 1.
Q2) This question is trying to confuse you, read it carefully. Each has a mass of 1kg
    Answer - 4.
Q3) Lead is a solid that is hardly malleable. Cotton balls are made of solid cotton strands but these can be shaped   
    by hand. Water is a liquid which can be moved and adjusted. The way to understand this question is to know   
    which will float in water, if it floats, water is more dense, if it sinks, water is less dense.
    Answer - 2.

- Spannerman
 

Offline NothaShrubry

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« Reply #3 on: 23/02/2010 17:22:09 »
Carbon in graphite is not bonded to three other carbons! This misunderstanding arises from our faulty interpretation of what a "chemical bond" is - the idea of a discrete pair of electrons lying calmly between two adjacent atoms. This is not what bonds really do!

The thing is, diamond bonds can be simply described using a Lewis structure (lines drawn for bonds), where each carbon is bonded to four other carbons in a cubic close-packed arrangement.

Not so for graphite.

It is best seen as layers of hexagons (each carbon directly bonded to three other carbons) with a delocalised sheet of electrons "gluing" the sheets together.

Some people like to draw dotted lines ("half bonds") between carbons in the layers to the layer above and below, however, this leads to the misleading assumption that the layers are eclipsing (one carbon directly above another), where in fact they are staggered/out of registry. Thus each carbon is vertically above the empty hexagon in the carbon layer below it and these "half bonds" would join carbons in one sheet to carbons in a sheet two or more layers above or below.
 

Offline Spannerman

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« Reply #4 on: 23/02/2010 18:37:38 »
I understand what you are saying but if you look at the structure of graphite, <http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGFigs/3_18graph.gif [nofollow]>
Each carbon is linked/bonded to three other carbons on a lateral plane, this makes up a flat layer. These flat layers then have weak ionic attractions between them which make graphite so slippery and easily broken up.

 

Offline lightarrow

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« Reply #5 on: 23/02/2010 18:55:55 »
I understand what you are saying but if you look at the structure of graphite, <http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGFigs/3_18graph.gif>
Each carbon is linked/bonded to three other carbons on a lateral plane, this makes up a flat layer. These flat layers then have weak ionic attractions between them which make graphite so slippery and easily broken up.
Probably he intended to say that it's too simplistic to describe the difference between diamond and graphite just saying that each carbon is bound to 3 other carbons, in graphite. *The way* in which they are bound is absolutely significant here.
 

Offline Spannerman

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help with chemisty!
« Reply #6 on: 24/02/2010 17:03:33 »
Yes DiscoverDave, I agree!
 

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help with chemisty!
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