U.5 AND 6 SOLID STATE Flashcards
Metallic solids are a crystalline network formed by an…
ordered network of positive ions inmerse in an e- sea made of valence e-.
Properties of metallic solids?
- Soft or hard
- MP variates very low or high
- High thermal and electrical conductivities
- Malleable and ductile
What are the 2 types of crystal structure?
- CLOSED-PACKED STRUCTURES
- UNIT CELLS
What are the 2 tipes of closed-packed structures?
- HEXAGONAL CLOSE-PACKED (2 layers)
- CUBIC CLOSE-PACKED (3 layers)
What are the types of unit cells?
- CUBIC (a=b=c, all 90º)
- TETRGONAL (a=b!=c, all 90º)
- ORTHORHOMBIC (a!=b!=c, all 90º)
- MONOCLINIC (a!=b!=c, 2 angles 90º)
- HEXAGONAL (a=b!=c, 2 angles 90º, an other 120º)
- RHOMBOHEDRAL (a=b=c, all different from 90º but the same)
- TRICLINIC (a!=b!=c, all different from 90º and from each other)
Types of unit cells depending on the possition of the atoms?
- Simple cubic
- Body-centered cubic
- Face-centered cubic
How to calculate the number of atoms inside?
ni + 1/2 nf + X.nc
What is X in the formula to calculate the number of atoms inside?
Hexagonal close-packed - 1/8
Cubic closed-packed - 1/6
What is the coordination number(CN)?
Numer of atoms that are connected to the central atom.
What is CN for a simple cubic?
6
What is CN for a body-centered cubic?
8
What is CN for a face centered cubic?
12
What is CN for a hexagonal close-packed?
12
The electron sea model accounts for the….
electrical conductivity of metals and the easiness of deformation of metals.
The band theory is based on the..
MO theory
In the band theory if n orbitals are large the separation between levels is…
small, giving a continious band energy.
In the band theory the filling of the band depends on the…
e- give by the metal.
As the energy difference between levels is very small, electrons can be easily excited between the highest filled levels to the empty levels immediately above them. This effect accounts for the….
electrical and thermal conductivity.
The enormous number of levels in the band allows the absorption of radiation of any wavelength, and also its emission, accounting for the ….
metal shine
What are the two types of semiconductors?
- Intrinsic semiconductors
- Extrinsic semiconductors
THe behaviour of the intrinsic semiconductors is base on the…
electrical structure of the pure atom.
THe behaviour of the estrinsic semiconductors is modulated by the…
presense of small amounts of other atoms (impurities)
Types of extrinsic semiconductors?
P-type semiconductors (aceptor level)
N-type semiconductors (donor level)
Covalent network solids are formed by…
atoms covalently bonded.
