Intermolecular Forces Flashcards
What determines stater of matter
Distance between particles
What is the condensed phase?
Liquids and gases
What happens when pressure is increased
Liquification/solidification
What happens during phase change?
Heat increases the kinetic energy of the particles until the phase change occurs. During this part of the graph, KE remains constant and the heat increased the potential energy as the heat is used to pull apart the molecules
What is deposition
Gas to liquid
What is heat of fusion and heat of vaporisation?
Energy needed during melting from solid to liquid
Energy at boiling point that is required to convert a liquid to a gas
What is polarisability?
Tendency of an electron cloud to distort. Increasing this increases LDF
What does polarity affect?
MP, BP, solubility and chemical reactivity
What must features must polarity have?
Have at least 1 polar bond and must NOT be symmetrical (C surrounded by 4 Cl-
How does increased Mr affect LDF?
A larger molecule has more electrons thus the size of the induced dipole will be larger because there is greater polarisability and they can have greater fluctuations
Electrons are further away from the nucleus meaning they can move around easier and are more likely to from instantaneous/induced dipoles
How does surface area affect LDF
Lower surface area eg linear molecules have stronger LDFs as there are greater chances for interactions
What factors affect dipole-dipole interactions?
Increased polarity increased the interactions causing an increased BP
They are stronger than LDF if the polar molecules have similar size
What is change in electronegativity
Different between the electronegativity of the two atoms in the molecule
What causes LDF
Interactions between instantaneous and induced dipoles
How do LDFs take place?
Occasionally an excess of electrons will accumulate one side of the atom/side and a shortage on the other causing an instantaneous dipole.
These electrons will repel those of another atom causing the same and resulting in an induced dipole
What is the ion-dipole interaction?
Jon’s interacting with a partial charge in a polar molecule eg. Salt dissolving in water
What is hydrogen bonding?
Hydrogen atom interacts with an unshared electron pair on and F, N and O that are small and very electronegative
Explain the trend in H bonding
F—-H > H—-O > H——-N
Fluorine is the MOST electronegative and the HF bond is the most polar and strong BUT HF has only two lone pairs but only 1 Hydrogen.
Oxygen has 2 lone pairs and 2 hydrogens so it can make more H bonds than HN
N has only 1 lone pair, therefore not enough H
Boiling point of H20 is higher than HF
How does H bonding take place?
Hydrogen ‘gives away’ it’s electrons to the other atom exposing its nucleus and allowing it to interact with a lone pair
Why is ice denser than water?
I’ve has an open lattice structure as oxygen can bind 4 hydrogen atoms therefore it is less dense that H20
What is vapour pressure?
The pressure exhorted by a vapour that is in equilibrium with its solid or liquid phases eg. Liquid molecules evaporate at the same rate that the vapour is condensing
What affects VP?
Temperature due to increase KE of liquid molecules escaping as vapour
Tell me about volatile liquids?
They evaporate easily and have a high VP
What is boiling point?
Temperature when vapour pressure = atm pressure therefore it changes at different altitudes
