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Questions and Answers
What is the term used to describe a solid material with highly ordered constituents arranged in a three-dimensional network?
What is the term used to describe a solid material with highly ordered constituents arranged in a three-dimensional network?
How is supersaturation of a solution typically achieved for the process of crystallization?
How is supersaturation of a solution typically achieved for the process of crystallization?
Which type of solid has particles arranged randomly?
Which type of solid has particles arranged randomly?
What is the term used for the positions occupied by particles in a crystal lattice?
What is the term used for the positions occupied by particles in a crystal lattice?
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In which type of solid material are entities arranged in a regular pattern?
In which type of solid material are entities arranged in a regular pattern?
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What are all crystals made up of, in terms of repeating units?
What are all crystals made up of, in terms of repeating units?
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What term is used to describe the overall shape of a crystal?
What term is used to describe the overall shape of a crystal?
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In a body-centred unit cell, where are the atoms located?
In a body-centred unit cell, where are the atoms located?
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How do the crystals of a substance vary?
How do the crystals of a substance vary?
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Under what conditions do crystal habits acquire specific shapes?
Under what conditions do crystal habits acquire specific shapes?
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What type of crystals does Ibuprofen form when crystallized from hexane?
What type of crystals does Ibuprofen form when crystallized from hexane?
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Which type of unit cell has atoms at the center of every face?
Which type of unit cell has atoms at the center of every face?
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What type of information does a unit cell contain?
What type of information does a unit cell contain?
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In a crystal, what are the faces bound by called?
In a crystal, what are the faces bound by called?
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How many chloride ions surround each sodium ion in a sodium chloride unit cell?
How many chloride ions surround each sodium ion in a sodium chloride unit cell?
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Which type of unit cell has atoms or molecules only at each corner?
Which type of unit cell has atoms or molecules only at each corner?
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What is characteristic of a centered unit cell?
What is characteristic of a centered unit cell?
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Which types of unit cells are drug molecules likely to form?
Which types of unit cells are drug molecules likely to form?
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Study Notes
Unit Cell
- A unit cell is a representative part of a lattice that contains all the necessary information to define how the pattern is repeated
- All unit cells in a specific crystal are the same size and contain the same number of molecules or ions, arranged in the same way
- Unit cells can be divided into two classes: primitive unit cells and centered unit cells
Primitive and Centered Unit Cells
- Primitive unit cells: constituent particles (atoms or molecules) are present only at the corner positions of the unit cell
- Centered unit cells: one or more constituent particles are present at positions other than corners in addition to those at corners
- There are seven possible primitive unit cells with atoms or molecules only at each corner of the unit cell
- Centered unit cells can have atoms or molecules at the center of the top or bottom faces (end-centered), at the center of every face (face-centered), or with a single atom in the center of the cell (body-centered)
Crystal Form and Crystallization
- Most APIs are crystalline in nature and are produced by crystallization
- The physical properties of the solid state in crystals and powders of both drugs and pharmaceutical excipients are important as they can affect production of dosage forms and performance of the finished product
- Crystals of a given substance may vary in size, shape, relative development of faces, and number and kind of faces present
- The overall shape of the crystal is termed the crystal habit, which depends on the conditions of crystallization, such as solvent used, temperature, and concentration and presence of impurities
Crystallization Process
- Crystallization is mostly accomplished by creating a state of supersaturation of solute in a solution
- Supersaturation of solution can be achieved by cooling, evaporation, or a chemical reaction that changes the nature of the solute
- Crystallization is achieved through spontaneous formation or extraneous addition (seeding) of crystal nuclei
- Crystal growth occurs round the nuclei when solute is transferred from the solution to the crystal state (a reverse dissolution process)
Crystal Structure
- A crystal or crystalline solid is a solid material whose constituents (atoms, molecules, or ions) are arranged in a highly ordered array forming a three-dimensional network that extends in all directions
- The three-dimensional arrangement is called a crystal lattice
- The positions occupied by particles in a crystal lattice are called lattice sites or lattice points
- The crystal lattice is a collection of lattice points, with molecules and atoms held together by noncovalent interactions
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Description
Test your knowledge on crystal unit cells and lattices. Learn about how unit cells define the lattice pattern, the arrangement of molecules or ions, and the interfacial angles of crystals.
