metal crystals
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Metal Crystals. Crystal Structures. Metal 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. - PowerPoint PPT PresentationTRANSCRIPT
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.