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Ionic Compounds

by Jadaav
Tags: compounds, ionic
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Jadaav
#1
Aug7-12, 01:35 PM
P: 158
Why are ionic compounds hard and brittle ?

For instance, an alloy is a mixture of 2 or more elements and thus does not break easily relative to original elements. Shouldn't the ionic compounds also be like the alloys ?
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Amok
#2
Aug9-12, 04:18 AM
P: 255
Quote Quote by Jadaav View Post
Why are ionic compounds hard and brittle ?

For instance, an alloy is a mixture of 2 or more elements and thus does not break easily relative to original elements. Shouldn't the ionic compounds also be like the alloys ?
An alloy usually involves metallic elements and metallic bonding, very different from ionic bonding. I think ionic compounds are hard and brittle, because its component atoms are very strongly bound to each other and form a crystal structure, which means atoms don't have much leeway to move. In mettallic compounds, on the other hand, atoms are as if swimming in a sea of their (and other atom's) electrons, meaning they can slide and move morea easily.
chill_factor
#3
Aug11-12, 05:36 AM
P: 899
imagine a crystal of alternating Na+ and Cl- ions. You take a hammer and hit it. The Na+ and Cl- ions move around their equilibrium points, as you expect, and return to equilibrium after vibrating. However if you hit the crystal hard enough, you'll dislocate a section of it that happens to align Na+ on one face to Na+, and you get electrostatic repulsion that breaks the crystal apart very quickly. This is the rough reason for why cracks propagate extremely quickly in ionic crystals.

Jadaav
#4
Aug13-12, 11:15 AM
P: 158
Ionic Compounds

Thanks to both of you :) I now understand how it works.

Concerning the dislocation of the lattice structure, What did you meant by " align Na+ on one face to Na+ " ?

Isn't the Na+ surrounded by 6 Cl- ions ?
sjb-2812
#5
Aug16-12, 02:27 AM
P: 427
Quote Quote by Jadaav View Post
Thanks to both of you :) I now understand how it works.

Concerning the dislocation of the lattice structure, What did you meant by " align Na+ on one face to Na+ " ?

Isn't the Na+ surrounded by 6 Cl- ions ?
Maybe in the depths of the lattice, yes, but what about on the edges / faces?
Jadaav
#6
Aug21-12, 12:59 PM
P: 158
So I presume each lattice isn't connected to each other by ionic bonding, am I right ?

One lattice has a layer on it ( inside which are the ions ) and which is could be cracked by hitting and then the whole object dislocating with electrostatic repulsion.

That's what I could imagine.


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