Lecture 12 (Lattices, etc.) Flashcards
What is an anion?
a negatively charged ion
What is a cation?
a positively charged ion
What is the most efficient arrangement of spheres in a rectangular box?
close-packed
What is close-packing?
one sphere is in contact with six neighbouring spheres from the same layer
What is cubic close-packing? (ccp)
every third layer is identical
What is hexagonal close-packing? (hcp)
every second layer is identical
What packing is the ABCABC arrangment?
cubic close-packing
What packing is the ABABAB arrangement?
hexagonal close-packing
What is a coordination number?
how many spheres a specific sphere touches
What is a unit cell?
the smallest repeating unit in a solid state lattice
What is the formula for the radius of a ccp?
a2 +a2 =(4r)2
where a is the unit cell edge
where r is the atomic (metallic) radius
What is an interstitial hole?
when close-packed structures contain octahedral and tetrahedral holes or sites
What noble gases crystallize under normal conditions in ccp structures?
Ne, Ar, Kr, Xe. and Rn
What noble gas crystallizes in a hcp structure?
He
What is polymorphism?
When a substance exists in more than one crystalline form
What is metallic radius?
It is half the distance between nearest-neighbour atoms in a solid-state metal lattice
What is metallic radius dependent on?
Coordination number
What does it tell us when a metal does not adopt a close packed structure?
It has a low melting point, low standard enthalpies of fusion, and low standard enthalpy of atomization
What is an alloy?
It is an intimate mixture, a compound of two or more metals, ore metals, and non-metals.
What does alloying do?
It changes the physical properties and resistance to corrosion, heat, etc.
What is the result of rapid cooling (quenching)?
Random distribution of constituents (solid solution), with a major solvent and minor solute constituent
What is the result of rapid cooling (quenching)?
Random distribution of constituents (solid solution), with a major solvent and minor solute constituent
What is the result of slow cooling?
A more ordered arrangement
What is a substitutional alloy?
Atoms of the solute occupy sites in the lattice of the solvent. Atoms must be similar size and tolerate the same coordination number with atoms of solvent
What is an interstitial alloy?
Atoms of the solute occupy holes in the lattice of the solvent.
What is an intermetallic compound?
mixtures of metals that crystallize in a different lattice than each of its constituents
