Inorganic 1 Topic 11

Metallic Bonding and Crystallography

In the absence of … , electrically … metal … will pack as efficiently as possible in space

directional covalent bonds, neutral, atoms

Hard, non-… spheres of identical … form … layers

deformable, radii, close-packed

In hexagonal close packing, the third layer sits …

directly over the first layer

The HCP arrangement is usually referred to as an … layer repeat

ABA

Top and side view of HCP layers:

HCP unit cell:

What is the definition of a unit cell?

the smallest repeating unit (group of atoms) in a crystalline substance which has the overall symmetry of the crystal and from which the entire lattice can be built by repetition in three dimensions

In cubic close packing, the third layer sits …

over holes in the first layer

In cubic close packing, the fourth layer sits …

directly over the first layer

The CCP arrangement is usually referred to as an … layer repeat

ABC or ABCA

What is the arrangement of layers in a CCP arrangement?

CCP unit cell:

Cubic close packing is also known as …

face-centred cubic

What is the coordination number of an atom in a close packed arrangement (hexagonal or cubic)?

12

What percentage of the total volume is occupied by spheres in a close-packed arrangement (hexagonal or cubic)?

74%

What percentage of the total volume is occupied by spheres in a body-centred cubic arrangement?

68%

In a BCC arrangement, the spheres are arranged in layers based on … rows, rather than … rows, as in a close-packed arrangement

square, triangular

In BCC, the third layer sits …

directly over the first

BCC unit cell:

What is the coordination number of an atom in a BCC arrangement?

8

… solids are have a highly ordered shape, whereas … solids are less ordered

crystalline, amorphous

In crystalline solids, the atoms are in an … called a …

orderly array, lattice

Crystalline solids have a … internal arrangement

regular

Amorphous solids have their atoms in a … arrangement, or a …

random, mixture

Amorphous solids have structures which are similar in character to …

liquids

Properties of atomic crystalline solids:

• individual atoms held together by weak dispersion forces

• noble gases are the only examples

  • low melting and boiling point reflects weak forces between atoms

Properties of molecular crystalline solids:

• held together by intermolecular forces (dispersion, dipole-dipole, hydrogen)

• lattice points are occupied by individual molecules

Properties of ionic crystalline solids:

• ionic bonding

  • electrons are transferred between atoms to form cations and anions

• solid is held together by electrostatic forces between the ions

Properties of metallic crystalline solids:

• metals conduct electricity freely, via motion of electrons

• metals can be considered as a sea of electrons surrounding an array of cations

• held together by electrostatic interactions between electrons and cations

• interactions are maximised when the cations are close packed

Properties of network covalent crystalline solids:

• atoms are joined by strong covalent bonds which extend throughout the solid forming a network

• hard, rigid materials

In metallic bonding, … electrons lead to … bonding

delocalised, non-directional

Non-directional bonding in metals leads to which properties?

malleability and ductility

The mobility of delocalised electrons results in which properties?

electrical and thermal conductivity

What is an alloy?

a blend of metals (or a metal and another element) that is prepared by mixing the molten components and then allowing to cool

In an alloy, the elements have been mixed at an … level

atomic

What does the term “solid solution” mean?

a term for a solid with elements mixed at the atomic level

homogeneous mixture of two compounds in solid state and having a single crystal structure

What is a substitutional alloy?

atoms of the solute metal randomly occupy sites in the solvent metal lattice (shown in orange)

In order for a substitutional alloy to form, the metal radii must be …, normally within … of each other

similar, 15%

In order for a substitutional alloy to form, the … metal must tolerate the … environment of the … lattice

solute, coordination, host

In order for a substitutional alloy to form, the … characteristics of the two metals must be similar, otherwise … may occur and the formation of an … compound is more likely

electropositive, charge transfer, ionic

What is an interstitial alloy?

some holes between the metals in the lattice are occupied by another element

What is a crystal structure?

the name given to the unit cell and the particular arrangement of atoms within it (e.g. HCP, CCP, BCC)

What is a structure type?

a defined arrangement of atoms, for example the NaCl structure type is common for many AX atom combinations

Unit cells are defined by three … (a, b, c) and three … (α, β, γ)

vectors, angles

Cubic unit cells are defined by which vectors and angles?

a = b = c, α = β = γ = 90

Hexagonal unit cells are defined by which vectors and angles?

a = b ≠ c, α = β = 90, γ = 120