Lecture 12 (Lattices, etc.)

Question 1

What is an anion?

Answer 1

a negatively charged ion

Question 2

What is a cation?

Answer 2

a positively charged ion

Question 3

What is the most efficient arrangement of spheres in a rectangular box?

Answer 3

close-packed

Question 4

What is close-packing?

Answer 4

one sphere is in contact with six neighbouring spheres from the same layer

Question 5

What is cubic close-packing? (ccp)

Answer 5

every third layer is identical

Question 6

What is hexagonal close-packing? (hcp)

Answer 6

every second layer is identical

Question 7

What packing is the ABCABC arrangment?

Answer 7

cubic close-packing

Question 8

What packing is the ABABAB arrangement?

Answer 8

hexagonal close-packing

Question 9

What is a coordination number?

Answer 9

how many spheres a specific sphere touches

Question 10

What is a unit cell?

Answer 10

the smallest repeating unit in a solid state lattice

Question 11

What is the formula for the radius of a ccp?

Answer 11

a2 +a2 =(4r)2
where a is the unit cell edge
where r is the atomic (metallic) radius

Question 12

What is an interstitial hole?

Answer 12

when close-packed structures contain octahedral and tetrahedral holes or sites

Question 13

What noble gases crystallize under normal conditions in ccp structures?

Answer 13

Ne, Ar, Kr, Xe. and Rn

Question 14

What noble gas crystallizes in a hcp structure?

Answer 14

He

Question 15

What is polymorphism?

Answer 15

When a substance exists in more than one crystalline form

Question 16

What is metallic radius?

Answer 16

It is half the distance between nearest-neighbour atoms in a solid-state metal lattice

Question 17

What is metallic radius dependent on?

Answer 17

Coordination number

Question 18

What does it tell us when a metal does not adopt a close packed structure?

Answer 18

It has a low melting point, low standard enthalpies of fusion, and low standard enthalpy of atomization

Question 19

What is an alloy?

Answer 19

It is an intimate mixture, a compound of two or more metals, ore metals, and non-metals.

Question 20

What does alloying do?

Answer 20

It changes the physical properties and resistance to corrosion, heat, etc.

Question 21

What is the result of rapid cooling (quenching)?

Answer 21

Random distribution of constituents (solid solution), with a major solvent and minor solute constituent

Question 21

What is the result of rapid cooling (quenching)?

Answer 21

Random distribution of constituents (solid solution), with a major solvent and minor solute constituent

Question 22

What is the result of slow cooling?

Answer 22

A more ordered arrangement

Question 23

What is a substitutional alloy?

Answer 23

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

Question 24

What is an interstitial alloy?

Answer 24

Atoms of the solute occupy holes in the lattice of the solvent.

Question 25

What is an intermetallic compound?

Answer 25

mixtures of metals that crystallize in a different lattice than each of its constituents