Molecular Crystals
This post is an introduction to molecular (focus on Organic) crystals; what they are, how they form, and their properties.
Definition
A molecular crystal is a solid substance consisting of individual organic (usually) molecules in a particular arrangement (in essence, structure) that repeats itself across the entire volume of the substance. Pharmaceutical compounds are a common example.
Formation
A particular structure is a result of individual molecules arranging themselves (that is, entire molecule rotating and single bonds rotating) such that a maximum number of intermolecular bonds form with the highest overall bonding energy possible. Formation of the intermolecular bonds is a result of Van Der Waals forces, which include London-Dispersion and polar attractions.
Crystal Binding Energy
The total intermolecular bonding energy of a molecular crystal, therefore, is a function of:
1) Number of individual intermolecular bonds formed (which can far-outnumber the number of individual molecules) and
2) the Sum-Total of intermolecular bond energies, which depends, in part, on the distances between atoms participating in the intermolecular bonding.
In turn, the two points (actually three), mentioned above, depend on:
A) The size of each compound molecule and
B) The number of functional groups for each molecule vs. "organic-nature" (relative size of carbon chain portion)
Atomic-Level Characteristics
Two separate cases must be considered: Molecules with - 1) greater polarity vs. 2) lower polarity (more "organic-nature").
Greater Molecular Polarity
Compound molecules (with more polar functional groups) tend to produce crystals consisting of more intermolecular bonds and greater total bond energy. A greater number of functional groups per molecule can cause the overall binding energy to increase; because many functional groups contribute to polar bonding.
Lower Molecular Polarity
Increasing Molecular Weight increases total binding energy in the form of increased Van der Waals forces. One must keep in mind, however, that many longer carbon chain molecules do not form solid crystals.
Properties
Here is a short list of crystal properties and how they relate to atomic-level characteristics:
Water Solubility - Degree of polar-bonding and number of molecules packed together
Density - number of molecules packed together
Melting Point - Overall Crystal Binding Energy
Future posts will cover these topics. Thank you for reading.
This post is an introduction to molecular (focus on Organic) crystals; what they are, how they form, and their properties.
Definition
A molecular crystal is a solid substance consisting of individual organic (usually) molecules in a particular arrangement (in essence, structure) that repeats itself across the entire volume of the substance. Pharmaceutical compounds are a common example.
Formation
A particular structure is a result of individual molecules arranging themselves (that is, entire molecule rotating and single bonds rotating) such that a maximum number of intermolecular bonds form with the highest overall bonding energy possible. Formation of the intermolecular bonds is a result of Van Der Waals forces, which include London-Dispersion and polar attractions.
Crystal Binding Energy
The total intermolecular bonding energy of a molecular crystal, therefore, is a function of:
1) Number of individual intermolecular bonds formed (which can far-outnumber the number of individual molecules) and
2) the Sum-Total of intermolecular bond energies, which depends, in part, on the distances between atoms participating in the intermolecular bonding.
In turn, the two points (actually three), mentioned above, depend on:
A) The size of each compound molecule and
B) The number of functional groups for each molecule vs. "organic-nature" (relative size of carbon chain portion)
Atomic-Level Characteristics
Two separate cases must be considered: Molecules with - 1) greater polarity vs. 2) lower polarity (more "organic-nature").
Greater Molecular Polarity
Compound molecules (with more polar functional groups) tend to produce crystals consisting of more intermolecular bonds and greater total bond energy. A greater number of functional groups per molecule can cause the overall binding energy to increase; because many functional groups contribute to polar bonding.
Lower Molecular Polarity
Increasing Molecular Weight increases total binding energy in the form of increased Van der Waals forces. One must keep in mind, however, that many longer carbon chain molecules do not form solid crystals.
Properties
Here is a short list of crystal properties and how they relate to atomic-level characteristics:
Water Solubility - Degree of polar-bonding and number of molecules packed together
Density - number of molecules packed together
Melting Point - Overall Crystal Binding Energy
Future posts will cover these topics. Thank you for reading.
No comments:
Post a Comment
Comments or Questions? Feedback is always welcome!