metal crystals

Metal CrystalsMetal Crystals

Metallic BondingFormed between atoms of

metallic elementsGood conductors in all states,

lustrous, relatively high melting points, malleable.

Examples; Na, Fe, Al, Au, Co

Structure of Metals Metallic atoms have low electronegativities - lose

their valence electron(s) easily Once a metallic atom loses its outer shell

electron(s) it becomes a positively charged kernal.

Metallic lattice structures are made up of an array of kernals.

The electrons from each metallic atom are found in a common pool or “sea” and are free to move between all the kernals.

They are called delocalized electrons.

Metallic Bonding - A Sea of Delocalized Electrons

Crystal StructuresMetal kernals are viewed as hard

spheres. The packing pattern adopted provides

the greatest energy stability.Ions in salts are also hard spheres The packing pattern is the same as

metals, now the larger ion. The smaller ion is placed in the

“holes” of the structure instead of electrons.

Unit Cells Crystals consist of repeating units

which may be atoms, ions or molecules. The space lattice is the pattern formed

by the points that represent these repeating structural units.

Packing typesEach Metal kernal

has:

Body Centered 8 nearest neighbors. 68% packing

efficiency Alkali metals pack

this way, most malleable

Close Packed- Face centered cubic- Hexagonal cubic

12 nearest neighbors.

Hexagonal Close Packing Alternating planes of

hcp spheres Those in the 3rd plane

pack directly above those in the 1st plane – ABA pattern

74% of the space is filled by metal kernals, the rest is filled by electrons.

used by Be, Co, Mg, Zn, Sc, Ti, Cd & Zr

Least malleable packing

Face Centered Packing Identical to hexagonal

packing, EXCEPT the 3rd spheres are in the holes that were not used to form the 2nd plane

The 4th plane is above the 1st plane – ABCA

Used for Ag, Al, Au, Ca, Cu, NI, Pb and Pt Less malleable than face centered cubic

Close PackingClose Packing

AlloysAlloys

Alloys are solid solutions of metals.They are usually prepared by mixing molten components.

They may be homogeneous, with a uniform distribution, or occur in a fixed ratio, as in a compound with a specific internal structure.

Substitutional AlloysSubstitutional Alloys

Substitutional alloys have a structure in which sites of the solvent metal are occupied by solute metal atoms.

An example is brass, an alloy of zinc and copper.

Substitutional AlloysSubstitutional Alloys

These alloys may form if:1. The atomic radii of the two

metals are within 15% if each other.

2. The unit cells of the pure metals are the same.

3. The electropositive nature of the metals is similar (to prevent a redox reaction).

Interstitial AlloysInterstitial AlloysInterstitial alloys are solid

solutions in which the solute atoms occupy holes (interstices) within the solvent metal structure.

An example is steel, an alloy of iron and carbon.