Chapther 1 crystal structures Flashcards
What are the two types of interstitial sites in cp structures?
Tetrahedral and Octahedral
How many orientations of tetrahedral sites are present in ccp structures?
Four equivalent orientations
What characterizes octahedral sites in crystal structures?
Coordinated to three anions in each layer, located midway between layers
What symmetry operation combines rotation and inversion?
Inversion axis
Which inversion axes are possible in crystals?
¯1, ¯2, ¯3, ¯4, and ¯6
What does the unit cell specification include?
Size, shape, and atomic coordinates
How is a primitive unit cell characterized?
Lattice points only at the corners
What is an example of a face centered cubic (fcc) structure?
Copper (Cu)
How are body centered cubic (bcc) structures distinguished?
They have an extra lattice point at the body center
What do lattice planes reference in crystal structures?
Imaginary planes providing a grid for atomic arrangement
What defines the interplanar d-spacing?
Distance between pairs of adjacent lattice planes
What is a common characteristic of NaCl’s crystal structure?
It is face centered cubic (fcc) and has Z = 4
What does the term ‘coordination number’ refer to?
The number of closest neighboring atoms surrounding an atom
What are the limitations of close packing models?
They cannot apply to all types of structures
Why might unit cells alone not be sufficient to describe a crystal?
They don’t provide a full 3D representation of the structure
What types of bonding might be considered when analyzing crystal structures?
Ionic, covalent, metallic, and van der Waals bonding
What does Bragg’s law relate to in crystallography?
The diffraction of X-rays by lattice planes
How many Na and Cl are effectively contained in the NaCl unit cell?
4 Na and 4 Cl
What do symmetry elements related to point symmetry include?
Mirror planes, centers of symmetry, and axes of rotation
What is a glide plane in crystal symmetry?
A symmetry operation that combines reflection and translation
In the context of lattice types, what is a C-centred lattice?
A lattice with extra points on one pair of opposite faces
What does a 21 screw axis represent?
A symmetry operation involving rotation and translation of half the axis length
How are atoms arranged in an octahedral site?
Four coplanar atoms with two above and below the plane
What concept is important for understanding crystal chemistry beyond unit cells?
Close packing and space-filling polyhedra
