Chapter 4 - Intermolecular Forces Flashcards
What are intermolecular forces?
Intermolecular forces are forces(push or pull) which mediate interaction between molecules, including forces of attraction or repulsion which act between molecules and other types of neighboring particles
Why is it important whether a molecule is polar or non-polar and the intermolecular forces it has on other molecules?
These are important in explaining the properties of substances
What are the different types of intermolecular forces and explain each one?
Explanations will not be provided below as they are too long.
Different types of intermolecular forces:
*Ion dipole forces
*Ion-induced forces
*Dipole-dipole forces
*Induced dipole forces
*Dipole-induced-dipole forces
Draw the graph with all the different types of intermolecular forces interacting with one another
Done?
Name the types of intermolecular forces that are considered van der Waals’ forces
Dipole-dipole forces
Induced dipole forces
Dipole-induces-dipole forces
What is different between intermolecular and intramolecular forces ? Explain with regard to the properties of each
Intermolecular forces:
- forces between molecules
- strength of bonds are relatively weak
- Large distance between each bond
Intramolecular forces:
- forces between atoms
- Strength of the bonds are strong
- short distance between the atoms
What is solubility?
Solubility is the ability to be dissolved in water
Name the intermolecular forces in order of strength from strongest to weakest
- Dipole - dipole forces (hydrogen bonding dipole-dipole forces are stronger than dipole-dipole forces without hydrogen bonding)
- Ion-dipole forces
3&4: Depends on the chemicals involved, but it is ion-induced dipole forces and dipole-induced-dipole forces - Induced dipole forces (weakest) aka London forces/ Momentary dipole forces/dispersion forces
What is the relation between a weak intermolecular force and surface tension, boiling points and evaporation
A weak intermolecular force will get evaporated quickly. It will also have a weak surface tension and a low boiling point
What are the factors that affect boiling and melting points in a molecule? And how?
The boiling and melting point of a molecule is determined by its molecular structure and surface area.
How: As the electron density of a dipole increases, so does the intermolecular forces which would increase its boiling and melting points. The round the molecule, the less polar it can become
What are alkanes?
Alkanes are organic compounds containing carbon and hydrogen bonded together. The carbon atoms link together to form chains of varying lengths
How does boiling point and melting point change in different alkanes?
The more carbon atoms there are in an alkane, the greater the surface area and the greater it’s melting and boiling points. The melting and boiling point increases as the number of carbon atoms increase.
What is the general formula for alkanes?
CnH2n+2
What is the simplest alkane in terms of simplicity and what is its formula?
Methane. CH4
Name 5 different alkanes and give their chemical formulas
Methane = CH4 Ethane = C2H6 Pentane= C5H12 Hexane= C6H14 Icosane= C20H42
How does the phase of an alkane change as molecular mass increases or decreases?
When molecular mass is low(I.e. there are few carbon atoms), the alkane’s phase is gas as the intermolecular forces are weak. As this molecular mass increases (the more carbon atoms), the alkane’s phase starts to change from gas to liquid and even solid as the intermolecular forces get stronger
How does the size of molecules impact the strength of its intermolecular forces?
As the size of a molecule increases, so does the intermolecular force
What is viscosity?
Viscosity is the resistance to flow of a liquid
What is the relationship between viscosity and intermolecular forces?
A substance with stronger substance Intermolecular forces will be more viscous than substances with weaker molecular forces
What is the relationship between viscosity and molecular size?
The more viscous a substance is, the larger the molecular size
What is density?
Density is mass per unit of volume
What is the relationship between density and the number of molecules in a unit volume? Explain?
The more molecules there are in a unit volume, the higher the substance’s density. This is because the strong intermolecular forces in a solid(most dense phase) pull the molecules together which results in a higher density
Explain thermal expansion
As substances are heated, the particles gain more kinetic energy and move around faster which causes the substance to expand
Explain thermal conductivity is metals and covalent molecular compounds
In metals, there are some free, delocalized electrons which help transfer the heat energy through the metal. In covalent molecular compounds, there are no free, delocalized electrons which help transfer heat through the substance
Explain why the melting point of oxygen(O2) is much lower than the melting point of Hydrogen Chloride(HCl)
Oxygen is non-polar and, and therefore, the intermolecular forces are induced dipole forces. Hydrogen chloride, however, is polar and has dipole-dipole forces. The intermolecular forces in hydrogen chloride is stronger than that of oxygen and since melting points increase as the intermolecular forces get stronger, oxygen has a melting point lower than Hydrogen Chloride
Explain why the boiling point of F2 is much lower than the boiling point of NH3
Boiling point is directly proportional to intermolecular forces. F2 is non-polar and therefore has induced dipole forces. These are very weak intermolecular forces. On the other hand, ammonia is polar and has hydrogen bonding which are the strongest intermolecular force. Since ammonia has a stronger intermolecular force, it’s boiling point will be higher
Explain why Sodium chloride is likely to dissolve in methanol(CH3OH)
Sodium chloride is an ionic compound and, therefore, has ionic bonds. Methanol is a polar molecule. As Sodium chloride is submerged in methanol, there are ion dipole forces. This intermolecular force cause the sodium cation to be attracted to the negative pole of methanol and the chlorine anions are attracted to the positive pole of methanol. This breaks the ionic bond between sodium and chlorine and causes it to dissolve in methanol
What properties of water cause it to behave differently from other compounds?
The properties of water that cause it to behave differently from other compounds include: microscopic structure of water, the shape of the molecule, it’s polar nature and the intermolecular forces that hold water molecules together
What type of bonds hold water molecules together?
Hydrogen bonds
What are the unique properties of water and explain each one?
1.Specific heat:
Water has a high specific heat meaning that a lot of energy must be absorbed by water before it’s temperature changes. Usually increasing the temperature of a substance means that the particles will move more quickly, but before this can be done, the intermolecular forces have to be disrupted and because hydrogen bonding is involved in water, a lot of energy is required to break this bond before heating up the molecule
- Absorption of infra-red radiation:
Water is able to absorb infra-red radiation from the sun. As a result of this, the oceans and other water bodies act as heat reservoirs and are able to help moderate the Earth’s climate. - Melting and boiling point:
The melting point of water is 0C and it’s boiling point is 100C. This large range is very important as water can exist as a liquid over a large range of temperature. - High heat of vaporization:
The strength of the hydrogen bonds between water molecules means that it has a high heat of vaporization as a lot of energy is required to break the hydrogen bonds, before it can change phase into a gas. - Less dense solid phase:
Another unusual property of water is that it’s solid phase is less dense than its liquid phase. While other materials contract when they solidify, water expands.
What is specific heat?
Specific heat is the amount of heat energy that is needed to increase the temperature of a unit mass of a substance by 1 degree.
What is heat of vaporization?
Heat of vaporization is the energy that is needed to change a given quantity of substance into a gas
What is the heat of vaporization for water?
40.65 KJ•mol^-1
