Atoms and Quanta Flashcards
Week 2
What is the name of the property m in italics?
mass/g
What is the name of the property M in italics?
molar/formula mass in g/mol
What is the name of the unit m?
metre
What is the name of the unit M?
molarity - mol/L
What is an extensive property?
Give an example.
Depends on the amount of matter in the sample.
Mass.
What is an intensive property?
Give an example.
Depends only type of matter in sample.
Temperature.
What is a unit cell?
Smallest possible repeating unit for a structure.
Name 3 cells cubic in symmetry.
alpha = beta = gamma = 90 degrees
a = b = c (sides)
Primitive = scc
Body-centred cubic = bcc
Face-centred cubic = fcc
How are the atoms in primitive/simple cubic unit cell arranged?
Atoms side-by-side then stacked on top.
How are atoms arranged in a body centred cubic unit cell?
Atoms on top translated by 1/2a and 1/2b
How are atoms arranged in a face-centred cubic unit cell?
Atoms over gaps in previous layers (ABC).
What does putting atoms over gaps in previous layers mean for a face-centred cubic?
Greater packing efficiency.
What is an ab-projection show?
(look at the summary sheets to see the diagrams)
A 2D representation of unit cell from above.
What is a co-ordination number?
Number of atoms in contact with central atom.
List the co-ordination numbers for scc, bcc and fcc.
scc = 6
bcc = 8
fcc = 12
How many atoms in each unit cell for scc, bcc and fcc?
scc = 1
bcc = 2
fcc = 4
How do you calculate the volume of a unit cell?
perameter cubed
What is the equation relating a to r for a scc?
(look at diagrams and Pythagoras’ theorem to see how each of these equations are derived)
a = 2r
What is the equation relating a to r for a bcc?
a = 4r/√3
What is the equation relating a to r for a fcc?
a = √8 r
What is crystallography?
The scientific study of crystals and their atomic structure.
What is X-ray crystallography?
A technique used to determine the atomic and molecular structure of a crystal.
What happens when X-rays are directed at a crystalline substance?
they are diffracted, creating a pattern that can be analysed to reveal the arrangement of atoms within the crystal.
What is diffraction?
The spreading of waves as they pass through an obstacle.
What happens when X-rays are directed at Young’s Slits?
(look at diagram on summary sheet and blue book for waves)
Slits generate circular waves = diffraction pattern.
Through circular wave crossovers:
Constructive interference - leads to bright lines (peak of 1st wave through peak of second, amplitudes added).
Between circular wave crossovers:
Destructive interference - leads to dark fringes (peak of 1st wave goes through trough of second, amplitudes cancel to 0).
What is Bragg’s law of X-ray diffraction?
(for derivation, look at summary sheet)
2dsinθ = nλ
dsinθ = path difference between waves
n = integer number of cycles
λ = wavelength of x-ray
