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PL1002 > Crystals > Flashcards

Crystals Flashcards

1
Q

Crystal with all lengths and angles = 90°

A

Cubic

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2
Q

Crystal with 2 lengths the same and all angles = 90°

A

Tetragonal

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3
Q

Crystal with all lengths different and all angles = 90°

A

Orthorhombic

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4
Q

Crystal with all lengths different and 2 angles = 90° and 1 angle not 90°

A

Rhombohedral

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5
Q

Crystal with 2 lengths the same and 2 angles = 90° and 1 angle = 120°

A

Hexagonal

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6
Q

Crystal with all lengths different and 2 angles = 90° and one doesn’t equal 90°

A

Monoclinic

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7
Q

All lengths different and all angles different

A

Triclinic

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8
Q

How many atoms are in primitive cubic cell?

A

1 (8 1/8ths)

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9
Q

How many atoms are in body-centred cubic cell?

A

2 (8 1/8ths + 1)

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10
Q

How many atoms are in face-centred cubic cell?

A

4 (8 1/8ths + 4 1/2s + 1)

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11
Q

What states does x-ray diffraction occur in?

A

Solid only

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12
Q

Bragg’s Law

A

nλ = 2d sinθ

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13
Q

What causes the scatter of x-rays in a crystal?

A

The electron cloud around the atoms

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14
Q

What does each diffraction spot correspond to?

A

A single point in the lattice

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15
Q

What is polymorphism?

A

When molecules are arranged in 2 or more different ways

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16
Q

In what ways can molecules be arranged differently?

A
  • Differences in orientation or conformation of the molecules
17
Q

How can polymorphism be detected?

A
  • Differences in x-ray diffraction pattern
  • Melting Point
  • Solubility
18
Q

What are 2 types of multi-component systems?

A

Solvates and hydrates

19
Q

How are different polymorphs prepared?

A

Manipulating conditions of crystallisation such as solvent, temperature, pressure, cooling rate and stirring rate)

20
Q

What processing process may cause polymorphic changes?

A

Milling, drying, compression and time

21
Q

What pharmaceutical properties are affected by polymorphism?

A

Density, melting point, hygroscopicity, apparent solubility

22
Q

What is bioavailability?

A

The rate and extent to which a substance is absorbed and circulated around the body

23
Q

How can polymorphic forms be characterised?

A

X-ray diffraction, microscopy, thermal analysis and spectroscopy

24
Q

What does DSC stand for and detect?

A

Differential Scanning Calorimetry can detect different melting points if they exist

25
Q

How are forms and temperature related?

A

As temperature increases, Form III changes to Form II which changes to Form I which finally melts

26
Q

What is Thermal Gravimetric Analysis?

A

Constant heating rate is used to show changes in weight with temperature or time

27
Q

What is Hot Stage Microscopy?

A

Can be used to detect melting point and loss of solvent and can be used to distinguish between solvates and polymorphs

28
Q

What is birefringence?

A

The ability to rotate plane polarised light and in Liquid crystals gives rise to 2 refractive indices.

29
Q

Why are there 2 refractive indices in liquid crystals?

A

Light has 2 waves at 90° to each other and when they strike the surface, the light splits and one wave takes a longer pathlength. This results in the light exiting the material at 2 places and are out of phase

30
Q

What does thermotropic mean?

A

Liquid crystal shows behaviour as a function of temperature

31
Q

What type of crystal is a nematic crystal?

A

A thread-like crystal which is thermotropic

32
Q

How are lyotropic crystals formed?

A

Formed in solutions

33
Q

What kind of ordering does smectic crystals have?

A

Layer ordering

34
Q

What kind of ordering does nematic crystals have?

A

Orientational ordering

35
Q

How does temperature change colour of cholesteric liquid crystals?

A

Reflected light is equal to pitch and the pitch depends on the temperature

36
Q

What has an effect on pitch in cholesteric liquid crystals?

A

Temperature, pressure and electric and magnetic fields

37
Q

What are the 2 essential structural features of a lyotropic liquid crystal?

A

Amphiphilic and 2 distinct regions within the molecule

38
Q
A

PL1002 (6 decks)

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