1.What is the relationship between crystal symmetry (point group) and unit cell
ID: 802705 • Letter: 1
Question
1.What is the relationship between crystal symmetry (point group) and unit cell symmetry?
2.What is the relationship between crystal symmetry (point group) and lattice symmetry?
3.What is the fundamental difference between point group operators and space group operators? Why do we need space group operators to describe the symmetry of crystal structures?
4.What is the relationship between crystal form and crystal structure? How do they both relate to crystal habit?
5.If you examine a crystal and see lots of symmetry, what can you infer about the crystal’s atomic structure? On the other hand, if you examine a crystal and see no symmetry, what can you infer about the crystal’s atomic structure?
Explanation / Answer
answer- the shape of the crsytal is defined by the presence or absence of crytal symmetry. and unit cell is defined is smallest unit of structure or pattern that is being repeated in the entire crystal. Crystal is composed ofnumerous unit cell. there is 4 types of symmtery operation
Rotation axes symmetry- 2 fold, 3 fold, 4 fold and 6 fold
mirron plane symmetry also known as plane of symmetry- axial and diagonal plane of symmetry
centre of symmetry- if an imaginary line that can be pass from any point on its surface though it centre. and point is found on line at equal distance beyond the centre of opposite side
rotoiversion symmetry- symmetry opertation generated by the rotation.
symmetry element of finite object that define the total symmetry of the object these known as point group symmetry.
crystal lattice- crystal lattice is an imaginary pattern of points in which each point has an environment that is identical to other point. there are 2 type of lattice symmetry
1- Bravis lattice
2- Non bravis lattice
point group- it is set of crystallographic symmetry operation. which includes rotation, and reflection. in which centre point fixed while moving other direction. there are 32 point group of various crytal system. so there is 32 morphological crystalline symmetries of 32 point group. it is symmetry notation in 2 dimension space.
space group- it is symmetry group in 3 dimensional space. or it may defined as description of crystal symmetry in 3 dimension. there 3 type of space grous
pure translations
screw axis.
glide plane
crystal form- when an outward appearence of the crystal.takes on a regular geometric shape is called crystal structure. it is major diagnostic properties of the mineral.
crystal strcuture is the arrangment of atoms within crystal. crystal structure is build up of unit cell. it is how unit cell is repeated in the in 3 dimensional on a lattice.
crystal habit- it is general shape of crystal which include irregulatities due to growth. crystal structure and crystal form together decribe the crystal habit. it necessary to know the basic arrangement of atoms with crystal and their outward appearence to determine its form.
after examine the crystal symmetry we hae find that it is an ordered arangement of atoms in 2 and 3 dimensional. and if there is no symmetry in the crystal tit means there is no repition of the crystal and no ordered arrangement of the atoms. So its crystal form will be amorphous.
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