Structure and bonding in solids Flashcards
what are the two categories solids are divided into?
amorphous solids
crystalline solids
What does amorphous solid mean?
- poorly defined shapes
- lack molecular ordering particles
What does crystalline solid mean?
- well defined shape
- because particles (atoms, ions, molecules) are precisely ordered
How are the particles in a crystal packed
tightly
in an orderly 3D array
what shape are the particles considered as?
spheres
the centre point of each sphere form a regular pattern throughout the crystal called….
crystal lattice
true or false; each lattice point has identical surroundings (view from each lattice point is the same)
true
What is the lattice which has the highest possible symmetry?
cubic system
How is the cubic system lattice obtained?
by filling space with a series of identical cubes;
the unit cells of the system
What does a single unit cell contain?
all the structural information about the crystal
true or false; a crystal could be constructed in principle by making a great many copies of a single unit cell and stacking them together.
true
How many types of 3D lattice can be formed and why?
7 types
- due to the symmetry constraints
What is the shape of the unit cells of each of the 7 types of 3D lattices?
parallelepiped
true or false; the unit cell is the smallest unit; that if repeated in all 3 directions gives an entire unit structure
true
what are the smallest unit cells called?
primitive unit cell
true or false; the corners of each unit cell is shared by seven other unit cells
true
- a total of one lattice point per unit cell
What describes the primitive unit cells fully?
3 edge lengths
three angles between those edges
what happens when when the primitive unit cell does not have all the symmetry elements in the crystal?
a larger non-primitive unit cell with all the appropriate symmetry elements is then chosen
in practice where are cubic lattices mostly found in?
metallic elements (mostly)
- some covalent compounds
- many ionic compounds
What are the 3 types of unit cells within the cubic system?
simple cubic unit cell
body centered cubic unit cell
face centered cubic unit cell
is the simple cubic unit cell a type of primitive unit cell?
yes
true or false; bcc and fcc unit cells are also examples of primitive unit cells?
no; false
- they are examples of non-primitive unit cells
what is the coordination number of each particle in a simple cubic unit cell?
6
What is the coordination number of each particle in a bcc unit cell?
8
What is the coordination number of each particle in a fcc unit cell?
12
true of false; for bcc the corner particles do not touch each other, rather they all touch the centre sphere
true
true or false; for fcc a particle lies at each corner and at the centre of each face but not in the centre of the cube
true
true or false; for fcc the particles at the corners touch those in the faces but not each other
true
how are unit cells placed?
they lie adjacent to each other throughout the crystal WITH NO GAPS
why does each corner of a unit cell make only 1/8 contribution to each unit cell
a particles at the corner is shared by 7 other unit cells in the lattice
why is a particle found at the face of a unit cell only make 1/2 of contribution to the unit cell?
because a particle on the face is shared by one other unit cell in the lattice
how many atoms does a simple cubic unit cell have? (be able to calculate)
1
how many atoms does a bcc unit cell have? (be able to calculate)
2
how many atoms does a fcc unit cell have?
4
how much does an edge particle contribute to the unit cell?
1/4
true or false; the higher the coordination number of the particles in the crystal the greater the number of particles per volume (the more efficient the packing)
true
