Crystalline Solids Concept 2

Jules Bruno
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hey everyone. So when it comes to the cubic unit cell realize that there are three types of unit cell arrangements and they each possess different coordination numbers and packing efficiencies. Now, when we say coordination number, this is just the number of of neighboring atoms surrounding one atom in a crystal lattice here. If we take a view of a crystal lattice, let's have this as our atom of reference that atom we're gonna say because of this image, the coordination is equal to six. We're gonna say every atom In the Crystal Lattice is surrounded by six atoms themselves. And when we say packing efficiency, we're gonna say packing efficiency is the percentage of occupied atoms by occupied space by Adams in a unit cell. Now we're going to say the trend is, the greater the complexity then the larger the coordination number will get. And as a result of this, we're gonna have a larger packing efficiency here, we have an image of three typical types of cubic unit cells. And as we go from left to right, we can see that the cubes themselves get filled in more and more. They're becoming more and more complex with these blue regions representing additional atoms that can be comprised within a particular unit cell. So just remember as we're heading from left to right, we have an increase in complexity which will result in larger coordination numbers greater than six. And that would also result in a larger packing efficiency