Solids Flashcards

1
Q

Coordination of both cubic and hexagonal close packing?

A

12

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2
Q

Types of cubic close packed structures?

A

Face centred cubic
Primitive cubic
Body centred cubic

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3
Q

Fcc

A

atoms on each of the faces of the cube in addition to each of the eight vertices. Coordination number of 12.

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4
Q

Primitive

A

Atoms only on the vertices. Coordination number of 6, not close packed. Example of polonium.

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5
Q

Body centred

A

Atoms on vertices and one in the centre of he cube. Coordination number of 8, not close packed. Examples include sodium and potassium.

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6
Q

How many atoms contribute to the vertex and face in the cubic close packed unit cell?

A

Vertex 8 - share of 1/8 in the unit cell so contribute 8 x 1/8 to the unit cell
Face 6 - share of 1/2 in the unit cell so contribute 6 x 1/2 to the unit cell

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7
Q

Where do octahedral interstitials occur?

A

Lie between a triangle of atoms in the row love and another triangle of atoms in the two below

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8
Q

Where do tetrahedral interstitials occur?

A

Lie between a triangle of atoms in one row and a single atom in the other

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9
Q

Sodium chloride structure coordination numbers?

A

Both anions have coordination number of 6 and both have octahedral geometries, cubic close packed structure. Most group 1 halides have this structure and many oxides such as magnesium oxide and iron disulphide.

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10
Q

Fluorite structure coordinations numbers?

A

Based on cubic close packed, each Ca2+ has a coordination number of 8 in a cubic environment, each F- has a coordination number of 4 and is in a tetrahedral environment. Contains 4 Ca2+ ions and 8 F- ions, zirconium (IV) oxide and barium chloride adopt this structure.
Antifluorite is where the anions and cations switch place examples include sodium oxide and silver sulphide.

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11
Q

Nickel Arsenide structure coordination numbers?

A

Also called nickelling, based on hexagonal close packing, both nickel arsenic atoms have coordination number of 6 with nickel atoms having octahedral geometry, and trigonal prismatic around the arsenic atoms. Examples include cobalt (II) selenide, and nickel (II) telluride.

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12
Q

Spahlerite and wurtzite information?

A

Polymorphs of ZnS. Sphalerite is based on cubic close packing, wurtzite based on hexagonal close packing. In both cases the ions have coordination numbers of 4 and have tetrahedral geometry. Copper(I) chloride and silver(I) iodised adopts sphalerite. Zinc oxide, silicon carbide and boron nitride all adopt wurtzite structures.

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13
Q

Cadmium chloride and cadmium iodide information?

A

CdCl2 based on cubic close packing, CdI2 based on hexagonal close packing. Cd2+ ions with a coordination of 6 have octahedral geometry and fill alternating layers of octahedral sites, both form layered structures. The halide ions have a coordination number of 3 and trigonal pyramidal geometry.
Magnesium chloride and tantalum sulfide ave CdCl2 structuren. Lead(II) iodide and iron(II) bromide form the CdI2 structure.

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14
Q

Caesium chloride information?

A

Based on primitive close packing, all interstitial sites are equivalent. Have cubic geometry. Coordinations our both ions are 8. Formed by halides of singly charged cations, caesium bromide, thallium chloride.

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15
Q

Rutile information?

A

Polymorph of titanium dioxide, unit cell not cubic, titanium ions have coordination number of 6 with distorted octahedral geometry, oxide has coordination number of 3 and adopt trigonal planar geometries.

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16
Q

Perovskite structure A information?

A

CaTiO3, two possible structures. One potential is a primitive cubic Ca2+ on vertices, O2- on faces and Ti4+ in the centre. Ca2+ hs 8 atoms in unit cells, shares 1/8 to unit cell so total contribution is 1/8 x 8, Ti4+ has 1 atom in unit cell, and has a contribution of 1 to the unit cell, O2- has 6 atoms in the unit cell, shares 1/2 so contributes 6 x 1/2 to the unit cell.

17
Q

Perovskite structure B information?

A

Described as primitive close packing of Ti4+ ions on the vertices, O2- anions on the edges and Ca2+ ion in the centre.
Ti4+ hs 8 atoms in unit cells, shares 1/8 to unit cell so total contribution is 1/8 x 8, Ca2+ has 1 atom in unit cell, and has a contribution of 1 to the unit cell, O2- has 12 atoms in the unit cell, shares 1/4 so contributes 12 x 1/4 to the unit cell.

18
Q

Radius ratio rule?

A

r+/r-

19
Q

Linear radius ratio?

A

< 0.155

20
Q

Trigonal radius ratio?

A

0.155 - 0.225

21
Q

Tetrahedral radius ratio?

A

0.225 - 0.414

22
Q

Octahedral radius ratio?

A

0.414 - 0.732

23
Q

Cubic radius ratio?

A

0.732 - 1.000

24
Q

Cuboctahedral radius ratio?

A

> 1.000

25
Q

When is radius ratio not useful?

A

Incorrect predictions due to deviations from purely ionic solid eg GaAs, Si, C

26
Q

Lattice energy?

A

Difference in potential energy between ions in the solid lattice and the ions widely separated as a gas

27
Q

Born Lande equation?

A

Agreement between theoretical value by equation and experimental value is relatively good suggesting theory behind equation is a good way of describing ionic bonding

28
Q

How can Born Lande equation be used to show how ionic a compound is?

A

For ionic compounds with a large covalent character the Born Lande equation underestimates the lattice energy and the actual values obtained from a Born Haber cycle are considerably higher. This means the equation can be used as a way of estimating to what extent a compound is ionic,
THE CLOSER the value from the equation is to that from the Born Haber cycle the more ionic the compound is
LattU (calc) = Latt H (expt) –> low covalent character
LattU (calc) < Latt U (expt) –> high covalent character

29
Q

Why can Born Lande equation not be useful?

A

Need Madelung constant and inter ionic distances which may not be known - so Kapustinskii equation may be used instead

30
Q

Trends in ionic radii?

A

Anions generally bigger than cations
Ionic radii increases down a group with increasing principal quantum number
Cations get smaller with increasing chart
Anions get bigger with increasing charge

31
Q

Enthalpy change of formation?

A

Enthalpy change when one mole of product is formed in a reaction between the elements in their standard states

32
Q

Enthalpy change of atomisation?

A

Enthalpy change when one mole of element is converted into one mole of ions

33
Q

First ionisation enthalpy?

A

Enthalpy change when one mole of gas is converted into one mole of ions

34
Q

Electron gain enthalpy?

A

Enthalpy change when one mole of gas is converted into one mole of ions. Electron gain enthalpy is minus the electron affinity

35
Q

Lattice enthalpy?

A

Enthalpy change for conversion of one mole of ionic solid into gaseous ions