Lecture 12 (Lattices, etc.) Flashcards
(26 cards)
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
