Week 3 Ionic, Metallic, Molecular Solids & Crystal Structures Flashcards
how are ionic solids formed
transfer of electrons between atoms
what holds the ionic crystal together
attractive Coulomb potential
what is the Madelung potential
it is the sum of all pair-wise potentials
what is the general pair wise potential equation and explain the different notation
Uij = λexp[-rij/ρ] +- Qq/4πε0 1/rij
first term is the repulsive potential
second term is the coulomb potential
λ&ρ are parameters of repulsion
what is true of repulsion and what does this allow us to do
repulsion potential is usually only very short range so only need to consider interactions with nearest neighbours for repulsion
what is the total potential of ionic solids equation and explain the new terms
Utot = NUi = NΣUij = N(zλexp[-R/ρ] - αQq/4πε0R)
z is the number of nearest neighbours
R is the lattice constant and comes form rij = Rρij
α is the Madelung constant
what is the Madelung constant equation
α = Σ+- 1/ρij
how is the equilibrium separation found and the associated equation
finding the minimum potential
dU/dR|R0 = 0
what is the Madelung potential equation
UM = NαQq/4πε0R
what potential best describes molecular solids
Lennard Jones Potential
what is total potential of molecular solids equation
Utot = N4ε/2 Σ[(σ/ρijR)^12 - (σ/ρijR)^6]
what is the bonding in metallic solids
bonding between delocalised/valence electrons and metal ions
what does translational symmetry in a crystal structure suggest
the crystal has a periodic structure
what three parameters change and best describe a 2D lattice
|a|, |b| & φ
describe the length of the 2 sides and the angle they propagate between each other
define lattice and basis and crystal structure
lattice is the translational vector
basis is the atom/molecule
Crystal Structure = Basis + Lattice
