Chemical Influences
Experiment 12
Influences of Molecular Shape and Intermolecular Forces on Physical Properties
By
Hannah Kloss
Chemistry 112L- 01 --- Eric Boakye
November 10, 2014
Physical properties are properties that can be measured and seen in an object. An example of a physical property of an object would be the color, mass, solubility, volume, or the polarity of an object. A physical property can change the appearance of an object, but that does not mean that the chemical composition has to change. The chemical composition can remain the same. Physical properties are separated into two different categories. They are separated in to intrinsic properties and extrinsic properties. Extrinsic properties rely on the amount of material …show more content…
present. An example of extrinsic properties could be mass, weight, and volume. All of these properties are affected by the amount of material present. The opposite is true for intrinsic properties. Intrinsic properties are not directly affected by the amount of material present. Examples of intrinsic properties would include solubility, melting point, and conductivity. Intermolecular forces influence physical properties in an H2O molecule. This is because in all three phases of the water molecule the bond angles, hybridization, and molecular shape all stay the same, but the physical properties of the water molecule are different in each phase. Ice, water’s solid phase, is not easily compressed and has a well-defined volume and shape. When water is in its liquid phase it can take the shape of any container, can be slightly compressed, and has a definite volume. Finally, when water is in the gas phase it can be easily compressed, it will take the shape of any container, and does not have a definite volume. Intermolecular forces cause solid and liquid phases to form and intermolecular forces cause gases to diverge from ideal gas behavior. Intermolecular forces can also affect the physical property of polarity. Molecules can be polar or non-polar. Polar molecules will have a partial positive end and a partial negative end. This is also known as a dipole molecule. Polarity can also be affected by the molecular shape of the molecule. If the central atom is surrounded by the same element with no lone pairs on the central atom, then the molecule is most likely non-polar and the molecule will have the same molecular shape as the electron geometry. If the molecule has one or more lone pairs, this changes the molecular shape from the electron geometry depending on the amount of lone pairs. Intermolecular forces such as ion-dipole, dipole-dipole, dipole-induced dipole, and induced dipole-induced dipole or London Dispersion forces help decide what properties a molecule can have. Deciding which of these forces a molecule is depends on its polarity, whether it is polar or non-polar. This can be examined in a dipole diploe molecule. When two dipole molecules interact, the positive end of one of the molecules will be attracted to the partial negative end of the other molecule. This shows the molecules are held together by an opposite attraction.4 Intermolecular forces and molecular shape both affect the boiling points and melting points of molecules. A larger surface area, size, and structure will lead to the molecule having a higher boiling point than a molecule with a smaller surface area, size and structure. Intermolecular forces also increase in strength as a molecule gets smaller. The same intermolecular forces that affected the polarity of a molecule will also affect the boiling point of a molecule. These forces can include ion-ion, hydrogen bonding, dipole-dipole, and London dispersion forces. Boiling points and melting points can both be affected by ionic forces, for example. The attraction between positively charged ions and negatively charged ions are defined by Coulomb’s Law. Coulomb’s Law states that the higher the charge of an ion, the higher the polarity of the molecule. This makes the melting point of the molecule increase. Molecular shape can also influence the boiling point and melting point because of polarity. As polarity increases, the boiling point increases. Non-polar molecules, which tend to be molecules with just London dispersion forces, are going to have the lowest melting points. The opposite is true of the solubility of a molecule. If the size of a molecule increases, the melting point will also increase, but with solubility a larger surface area and size will make the molecule have a lower solubility. The larger the molecule, the lower the solubility of a molecule. The opposite is true of a molecule with a high polarity. If a molecule is more polar, the molecule will typically be more soluble in water. Viscosity is defined at the resistance of a liquid to flow.
A liquid with a high viscosity will not be able to flow well. For example, syrup or molasses both flow very slowly so they would have a high viscosity. Liquids such as water or alcohol would have a low viscosity because they flow very easily. Intermolecular forces that affect the molecules shape and composition will directly affect the viscosity of the molecule. An example of this can be observed between ethyl alcohol and ethyl glycol. Ethyl glycol has two more O-H groups than ethyl alcohol. The extra O-H groups effect the amount of hydrogen bonds in the ethyl glycol molecule. The ethyl glycol has more hydrogen bonds than ethyl alcohol. This gives the ethyl glycol molecule a higher viscosity than the ethyl alcohol molecule. Both kinetic energy and temperature can affect a molecule’s viscosity. When the temperature of a molecule is raised, the kinetic energy is also raised. When kinetic energy increases, molecules are more easily overcome by the forces that held the molecule together. This results in a decrease in viscosity. Viscosity is also affected by molecular shape. This is exemplified when n-pentane is compared to octadecane. Octadecane’s viscosity is higher than the viscosity of n-pentane. This is because octadecane’s molecules are irregularly shaped and disproportionate. The irregular shape and octadecane being disproportionate lead to octadecane being larger than n-pentane. This results in a higher viscosity. Also octadecane shares more intermolecular forces with the molecules surrounding it than with n-pentane. This also leads to octadecane having a higher viscosity than
n-pentane. There are many different factors that are involved in how intermolecular forces and molecular structure affect the physical properties of a molecule. There are many different physical changes that can happen to molecules. For example, changes in melting point, boiling point, viscosity, and solubility can be physical changes in a molecule. Though the appearance of a molecule can change from these physical changes, the chemical composition remains the same. The chemical composition can only be changed with a reaction or chemical change. Changes in the chemical composition of a molecule can come from flammability, toxicity, and oxidation. None of these factors can be changed by the alteration of a physical property. The changes of physical properties and chemical properties do not depend on each other. This means that when a physical property is changed, it doesn’t mean that the chemical properties will be changed.
Influences of Molecular Shape and Intermolecular Forces on Physical Properties
By
Hannah Kloss
Chemistry 112L- 01 --- Eric Boakye
November 10, 2014
Physical properties are properties that can be measured and seen in an object. An example of a physical property of an object would be the color, mass, solubility, volume, or the polarity of an object. A physical property can change the appearance of an object, but that does not mean that the chemical composition has to change. The chemical composition can remain the same. Physical properties are separated into two different categories. They are separated in to intrinsic properties and extrinsic properties. Extrinsic properties rely on the amount of material …show more content…
present. An example of extrinsic properties could be mass, weight, and volume. All of these properties are affected by the amount of material present. The opposite is true for intrinsic properties. Intrinsic properties are not directly affected by the amount of material present. Examples of intrinsic properties would include solubility, melting point, and conductivity. Intermolecular forces influence physical properties in an H2O molecule. This is because in all three phases of the water molecule the bond angles, hybridization, and molecular shape all stay the same, but the physical properties of the water molecule are different in each phase. Ice, water’s solid phase, is not easily compressed and has a well-defined volume and shape. When water is in its liquid phase it can take the shape of any container, can be slightly compressed, and has a definite volume. Finally, when water is in the gas phase it can be easily compressed, it will take the shape of any container, and does not have a definite volume. Intermolecular forces cause solid and liquid phases to form and intermolecular forces cause gases to diverge from ideal gas behavior. Intermolecular forces can also affect the physical property of polarity. Molecules can be polar or non-polar. Polar molecules will have a partial positive end and a partial negative end. This is also known as a dipole molecule. Polarity can also be affected by the molecular shape of the molecule. If the central atom is surrounded by the same element with no lone pairs on the central atom, then the molecule is most likely non-polar and the molecule will have the same molecular shape as the electron geometry. If the molecule has one or more lone pairs, this changes the molecular shape from the electron geometry depending on the amount of lone pairs. Intermolecular forces such as ion-dipole, dipole-dipole, dipole-induced dipole, and induced dipole-induced dipole or London Dispersion forces help decide what properties a molecule can have. Deciding which of these forces a molecule is depends on its polarity, whether it is polar or non-polar. This can be examined in a dipole diploe molecule. When two dipole molecules interact, the positive end of one of the molecules will be attracted to the partial negative end of the other molecule. This shows the molecules are held together by an opposite attraction.4 Intermolecular forces and molecular shape both affect the boiling points and melting points of molecules. A larger surface area, size, and structure will lead to the molecule having a higher boiling point than a molecule with a smaller surface area, size and structure. Intermolecular forces also increase in strength as a molecule gets smaller. The same intermolecular forces that affected the polarity of a molecule will also affect the boiling point of a molecule. These forces can include ion-ion, hydrogen bonding, dipole-dipole, and London dispersion forces. Boiling points and melting points can both be affected by ionic forces, for example. The attraction between positively charged ions and negatively charged ions are defined by Coulomb’s Law. Coulomb’s Law states that the higher the charge of an ion, the higher the polarity of the molecule. This makes the melting point of the molecule increase. Molecular shape can also influence the boiling point and melting point because of polarity. As polarity increases, the boiling point increases. Non-polar molecules, which tend to be molecules with just London dispersion forces, are going to have the lowest melting points. The opposite is true of the solubility of a molecule. If the size of a molecule increases, the melting point will also increase, but with solubility a larger surface area and size will make the molecule have a lower solubility. The larger the molecule, the lower the solubility of a molecule. The opposite is true of a molecule with a high polarity. If a molecule is more polar, the molecule will typically be more soluble in water. Viscosity is defined at the resistance of a liquid to flow.
A liquid with a high viscosity will not be able to flow well. For example, syrup or molasses both flow very slowly so they would have a high viscosity. Liquids such as water or alcohol would have a low viscosity because they flow very easily. Intermolecular forces that affect the molecules shape and composition will directly affect the viscosity of the molecule. An example of this can be observed between ethyl alcohol and ethyl glycol. Ethyl glycol has two more O-H groups than ethyl alcohol. The extra O-H groups effect the amount of hydrogen bonds in the ethyl glycol molecule. The ethyl glycol has more hydrogen bonds than ethyl alcohol. This gives the ethyl glycol molecule a higher viscosity than the ethyl alcohol molecule. Both kinetic energy and temperature can affect a molecule’s viscosity. When the temperature of a molecule is raised, the kinetic energy is also raised. When kinetic energy increases, molecules are more easily overcome by the forces that held the molecule together. This results in a decrease in viscosity. Viscosity is also affected by molecular shape. This is exemplified when n-pentane is compared to octadecane. Octadecane’s viscosity is higher than the viscosity of n-pentane. This is because octadecane’s molecules are irregularly shaped and disproportionate. The irregular shape and octadecane being disproportionate lead to octadecane being larger than n-pentane. This results in a higher viscosity. Also octadecane shares more intermolecular forces with the molecules surrounding it than with n-pentane. This also leads to octadecane having a higher viscosity than
n-pentane. There are many different factors that are involved in how intermolecular forces and molecular structure affect the physical properties of a molecule. There are many different physical changes that can happen to molecules. For example, changes in melting point, boiling point, viscosity, and solubility can be physical changes in a molecule. Though the appearance of a molecule can change from these physical changes, the chemical composition remains the same. The chemical composition can only be changed with a reaction or chemical change. Changes in the chemical composition of a molecule can come from flammability, toxicity, and oxidation. None of these factors can be changed by the alteration of a physical property. The changes of physical properties and chemical properties do not depend on each other. This means that when a physical property is changed, it doesn’t mean that the chemical properties will be changed.