Week 3 Ionic, Metallic, Molecular Solids & Crystal Structures Flashcards

1
Q

how are ionic solids formed

A

transfer of electrons between atoms

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2
Q

what holds the ionic crystal together

A

attractive Coulomb potential

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3
Q

what is the Madelung potential

A

it is the sum of all pair-wise potentials

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4
Q

what is the general pair wise potential equation and explain the different notation

A

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

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5
Q

what is true of repulsion and what does this allow us to do

A

repulsion potential is usually only very short range so only need to consider interactions with nearest neighbours for repulsion

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6
Q

what is the total potential of ionic solids equation and explain the new terms

A

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

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7
Q

what is the Madelung constant equation

A

α = Σ+- 1/ρij

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8
Q

how is the equilibrium separation found and the associated equation

A

finding the minimum potential

dU/dR|R0 = 0

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9
Q

what is the Madelung potential equation

A

UM = NαQq/4πε0R

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10
Q

what potential best describes molecular solids

A

Lennard Jones Potential

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11
Q

what is total potential of molecular solids equation

A

Utot = N4ε/2 Σ[(σ/ρijR)^12 - (σ/ρijR)^6]

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12
Q

what is the bonding in metallic solids

A

bonding between delocalised/valence electrons and metal ions

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13
Q

what does translational symmetry in a crystal structure suggest

A

the crystal has a periodic structure

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14
Q

what three parameters change and best describe a 2D lattice

A

|a|, |b| & φ

describe the length of the 2 sides and the angle they propagate between each other

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15
Q

define lattice and basis and crystal structure

A

lattice is the translational vector
basis is the atom/molecule
Crystal Structure = Basis + Lattice

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16
Q

what is a unit cell and primitive unit cell

A

unit cell is a parallelogram formed by lattice vectors

primitive unit cell is the most basic unit cell that can be formed not always the unit cell