Atoms and Quanta

Question 1

What is the name of the property m in italics?

Answer 1

mass/g

Question 2

What is the name of the property M in italics?

Answer 2

molar/formula mass in g/mol

Question 3

What is the name of the unit m?

Answer 3

metre

Question 4

What is the name of the unit M?

Answer 4

molarity - mol/L

Question 5

What is an extensive property?
Give an example.

Answer 5

Depends on the amount of matter in the sample.
Mass.

Question 6

What is an intensive property?
Give an example.

Answer 6

Depends only type of matter in sample.
Temperature.

Question 7

What is a unit cell?

Answer 7

Smallest possible repeating unit for a structure.

Question 8

Name 3 cells cubic in symmetry.
alpha = beta = gamma = 90 degrees
a = b = c (sides)

Answer 8

Primitive = scc
Body-centred cubic = bcc
Face-centred cubic = fcc

Question 9

How are the atoms in primitive/simple cubic unit cell arranged?

Answer 9

Atoms side-by-side then stacked on top.

Question 10

How are atoms arranged in a body centred cubic unit cell?

Answer 10

Atoms on top translated by 1/2a and 1/2b

Question 11

How are atoms arranged in a face-centred cubic unit cell?

Answer 11

Atoms over gaps in previous layers (ABC).

Question 12

What does putting atoms over gaps in previous layers mean for a face-centred cubic?

Answer 12

Greater packing efficiency.

Question 13

What is an ab-projection show?

(look at the summary sheets to see the diagrams)

Answer 13

A 2D representation of unit cell from above.

Question 14

What is a co-ordination number?

Answer 14

Number of atoms in contact with central atom.

Question 15

List the co-ordination numbers for scc, bcc and fcc.

Answer 15

scc = 6
bcc = 8
fcc = 12

Question 16

How many atoms in each unit cell for scc, bcc and fcc?

Answer 16

scc = 1
bcc = 2
fcc = 4

Question 17

How do you calculate the volume of a unit cell?

Answer 17

perameter cubed

Question 18

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)

Answer 18

a = 2r

Question 19

What is the equation relating a to r for a bcc?

Answer 19

a = 4r/√3

Question 20

What is the equation relating a to r for a fcc?

Answer 20

a = √8 r

Question 21

What is crystallography?

Answer 21

The scientific study of crystals and their atomic structure.

Question 22

What is X-ray crystallography?

Answer 22

A technique used to determine the atomic and molecular structure of a crystal.

Question 23

What happens when X-rays are directed at a crystalline substance?

Answer 23

they are diffracted, creating a pattern that can be analysed to reveal the arrangement of atoms within the crystal.

Question 24

What is diffraction?

Answer 24

The spreading of waves as they pass through an obstacle.

Question 25

What happens when X-rays are directed at Young’s Slits?

(look at diagram on summary sheet and blue book for waves)

Answer 25

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).

Question 26

What is Bragg’s law of X-ray diffraction?

(for derivation, look at summary sheet)

Answer 26

2dsinθ = nλ

dsinθ = path difference between waves
n = integer number of cycles
λ = wavelength of x-ray