40 Questions
What is the result of three successive processes in crystallization from solution?
Supersaturation, formation of crystal nuclei, and crystal growth.
What is a characteristic of crystalline solids?
They have highly ordered arrays of atoms or molecules.
What must happen in order to prepare a material in the amorphous state?
The material must be solidified quickly.
What is a characteristic of crystalline solids when they melt?
They melt sharply at a specific temperature.
What is a unit cell in a crystal?
A repeating unit in the crystal lattice.
What can happen to crystalline material when mechanical or thermal energy is supplied?
It becomes amorphous.
What are the units that constitute the crystal structure?
Atoms, molecules, or ions.
What is the difference between crystalline and amorphous solids?
Crystalline solids have a regular structure, while amorphous solids have a disordered structure.
What is the primary factor governing the physical state of a substance?
Intermolecular attraction forces
What is the purpose of the Real Gas Law?
To correct for ideal gas law assumptions
What type of bonding increases the attraction between molecules in liquids?
Hydrogen bonding
What is the term for different types of solids that have the same chemical composition but differ in their crystalline structure?
Polymorphism
What is the result of weak intermolecular forces in liquids?
Some ordering or regular arrangement among molecules
What is the term for solids that have a regular, three-dimensional arrangement of molecules?
Crystalline solids
What is the purpose of understanding polymorphism in pharmaceuticals?
To understand the pharmaceutical implications of polymorphism
What is the term for a phase that is intermediate between the solid and liquid states?
Mesophases
What is the main characteristic that distinguishes ionic crystals from molecular crystals?
Hardness and brittleness
What type of bonds hold together metallic crystals?
Metallic bonds
What is the term for the temperature at which a liquid passes into the solid state?
Melting point
What does the heat of fusion of ice being approximately 79.7 calories per gram mean?
It requires a lot of energy to change the state of ice to water
What is the trend observed in the melting points of normal saturated hydrocarbons (alkanes)?
They increase with increasing molecular weight
Why do alkanes with an even number of carbon atoms have higher melting points than those with an odd number of carbon atoms?
Because the molecules are packed more efficiently in the crystal
What is the main difference between ionic crystals and molecular crystals in terms of their physical properties?
Ionic crystals are hard and have high melting points, while molecular crystals are soft and have low melting points
What is the characteristic of metallic crystals that allows them to be good conductors of heat and electricity?
The presence of a 'sea' of electrons
What is a characteristic of amorphous materials compared to crystalline solids?
Glass transition temperature (Tg)
What is observed in the XRD pattern of crystalline solids?
Sharp diffraction peaks
What is the difference in stability between crystalline and amorphous materials?
Crystalline materials are more stable
What happens to amorphous materials as the temperature increases above Tg?
They become more rubbery
What is the purpose of X-ray diffractometry (XRD)?
To analyse the structure of solid materials
What is the difference in solubility between crystalline and amorphous solids?
Amorphous solids are more soluble
What is the glass transition temperature (Tg) associated with?
A change in the properties of the material
What is the characteristic of amorphous materials below Tg?
They are brittle
What is the characteristic of the amorphous form of a drug?
Higher solubility than crystalline form
What is the effect of polymorphism on a drug?
It affects therapeutic activity
What is an example of a crystalline solid subclass?
Polymorph
What is the definition of polymorphism?
Ability of solid materials to exist in two or more crystalline forms
What is a characteristic of polymorphs of the same drug?
They are chemically identical
What is the tendency of metastable polymorphs?
To transform into the most stable polymorph over time
What is a difference between different polymorphs of the same drug?
They have different melting points, XRD patterns, and solubility
What percentage of APIs are estimated to have more than one polymorphic form?
More than 50%
Study Notes
States of Matter
- Phase transitions: change from one state of matter to another
- Phase diagram: a graph that shows the relationship between temperature and pressure of a substance
- Intermolecular forces: forces that govern the physical state of a substance
Real Gas Law
- Corrects for ideal gas law assumptions about molecular interactions
- Equation: (P - a/V^2)(V + nb) = nRT
Liquid State
- Intermolecular forces of attraction in liquids (Van der Waals forces) impose some ordering or regular arrangement among molecules
- Hydrogen bonding increases attraction in liquids and affects their physicochemical behavior
Solid State
- Crystalline state: has regular structure that extends throughout the crystal
- Amorphous solids have disordered molecular structure
- Crystallization process: supersaturation, formation of crystal nuclei, and crystal growth
Crystalline Solids
- Crystals contain highly ordered arrays of atoms or molecules held together by certain interactions
- Unit cells: repeating units that constitute the crystal structure
- All unit cells in a specific crystal have the same shape and size, containing the same number of molecules or ions arranged in the same way
Types of Crystals
- Ionic crystals (e.g. NaCl): held together by ionic bonds
- Atomic crystals (e.g. C, Diamond): held together by covalent bonds
- Molecular crystals (e.g. CO2): held together by Van der Waal's forces
- Metallic crystals: lattice point occupied by metal atoms, positively charged ions in a field of freely moving electrons
Melting Point and Heat of Fusion
- Melting point: temperature at which a liquid passes into the solid state
- Heat of fusion: amount of heat energy required to change a unit mass of ice at its melting point into water at the same temperature
- Factors affecting melting point: molecular weight, van der Waals forces, and crystal structure
Amorphous Solids
- Do not have definite melting points, but have a glass transition temperature (Tg)
- Below Tg, the material is brittle and glassy; above Tg, the material is rubbery
- Amorphous solids can be converted from crystalline materials by mechanical or thermal energy
Solid-State Characterization
- X-ray diffractometry (XRD): a technique used to analyze the structure of solid materials
- XRD pattern: distinguishing feature between crystalline and amorphous solids
Pharmaceutical Difference between Crystalline and Amorphous Solids
- Stability vs therapeutic activity: crystalline materials have lower free energy and are more stable, while amorphous materials have higher free energy and are less stable
- Amorphous forms of drugs often have higher solubility and bioavailability than crystalline forms
Crystalline Solids Sub-classes
- Polymorphism: ability of solid materials to exist in two or more crystalline forms with different arrangements or conformations of the constituents in the crystal lattice
- Multicomponent crystals: hydrates, solvates, and cocrystals, which consist of more than one type of molecule
Learn about states of matter, vapor pressure, boiling point, solid state crystallinity, solvates, and polymorphism in pharmacy. Lecture 4 of Physical Pharmacy course.
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