28 Flashcards
Developments of atom model
Describe Dalton model
It is often referred to as the billiard ball model. He defined an atom to be a ball-like structure
Thomson’s model
the positively charged main mass is distributed evenly in the atom, whereas the negatively charged small electrons are moving in it.
Cathode ray tubes
- > Applying voltage
- > Causes a beam of particles flow from cathode to anode
- > The rays move toward the positively charged plates
Rutherford model
the majority of mass of an atom is in a small central volume with positive charge (nucleus) and the electrons are orbiting around it in circles gowerned by the Coulomb interaction.
Niels Bohr (1913) model
- Bohr’s model of the hydrogen atom is based on three postulates:
- (1) an electron moves around the nucleus in a circular orbit
- (2) an electron’s angular momentum in the orbit is quantized
- (3) the change in an electron’s energy as it makes a quantum jump from one orbit to another is always accompanied by the emission or absorption of a photon.
What is Pauli principle?
In multi-electron systems all electrons are in different quantum states.
→ no two electrons within an atom or molecule with identical quantum numbers.
Hund’s law:
in a given electron-configuration the lowest energy state is the one with the highest spin value (maximum multiplicity).
Liquids
there are only short-range order which is dynamic in nature.
→ Particles can roll on each other.
→ A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure.
→ Liquids are usually isotropic.
Crystalline materials:
long-range, periodic order exists with many repetition of an elementary cell.
Anisotropic.
Types of crystals based on band structures
What is forbidden gap
Energy gap between valence and conduction bands
What is . Fermi energy?
a hypothetical energy level for the electrons, related to a 50% occupancy.
Characteristics of conductors
Conductors are non-transparent as there are electrons in the conduction band which can absorbe visible photon energies.
Liquid crystal phases
What are Mesophases?
Mesophases can be characterized by the type of ordering.
- One can distinguish positional order (whether molecules are arranged in any sort of ordered lattice) and orientational order (whether molecules are mostly pointing in the same direction).
What is smectic phase?
Have
- positional order (whether molecules are arranged in any sort of ordered lattice)
- orientational order (whether molecules are mostly pointing in the same direction).
What is nematic phase?
only the orientational ordering is present
cholesteric or twisted nematic phase
a chiral order can be observed due to a fixed angle rotation of asymmetric molecules in the adjacent layers
2 examples of liquid crystals
- Thermotropic liquid crystals: the ordering depends on the temperature, present only in a certain temperature range.
-
Lyotropic liquid crystals: the ordering can be observed in certain concentration range, characteristic for
amphiphilic molecules.
Characteristics of Thermotropic liquid crystals
the ordering depends on the temperature, present only in a certain temperature range. (look at mesophase)
Characteristics of Lyotropic liquid crystals
The ordering can be observed in certain concentration range, characteristic for amphiphilic molecules.
What is a colloid?
It consists of two distinct phases, a continuous phase (the dispersion medium) and a particle phase
What is a colloid?
It consists of two distinct phases, a continuous phase (the dispersion medium) and a particle phase
