Flashcards in Lecture 2 Deck (76)
What are Hydrogen bonds?
Intermolecular, attractive forces, which are a type of polar bond
Where do H bonds occur?
Between Hydrogen and F, O and N.
These are very electronegative and suck electrons towards each other
What is a polar covalent bond?
An uneven sharing of electrons (more than covalent, but less than ionic)
Are H bonds stronger than most other van der waal forces?
What is the primary intermolecular force within liquid water?
Why does ice occupy more space than water?
As the temperature decreases below 4 degrees, It will strengthen the Hydrogen bonds between the water molecules so that they are more rigid.
As a result, they form a more open, crystallised structure with large spaces in between the bonds.
Thus ice occupies more space than water, hence a beer bottle in the freezer will pop
What factor affects the balance of forces of a molecule?
The distance between molecules
What is a net energy curve?
A curve of attraction and repulsive forces vs. distance
What does a net energy graph tell us?
as distance decreases, net energy becomes an attractive force, but there is still something which prevents the molecules from collapsing into each other
There is a distance where attraction forces equal repulsive forces.
How does temperature change the net energy graph?
As we heat ice and it melts, the shape of the curve will change.
Although the curves look different at different temperatures the shape/pattern remains the same.
i.e. molecules cant come too close together or repulsive forces will take over
What is the behaviour of gases?
They move in random directions and try to fill the space.
What causes the pressure of a gas?
gaseous molecules pushing the edge of the container
Why doesnt a balloon collapse when filled with air?
the molecules in the air are bouncing against the walls of the baloon to hold i out
What keeps the balloon in shape?
The balance between the gas molecules bouncing against the wall of the baloon, and the natural elastic recoil of the baloon
How does temperature affect the way gaseous molecules move?
If you increase temperature, gas molecules have more energy to move around. likewise if you decrease temperature, molecules move slowly.
So if you freeze a balloon it shrinks because molecules do not bounce against the walls as much due to lower temperature.
likewise if you throw a canister into fire, temperature will increase, causing molecules to move faster, resulting in increased pressure which can cause the canister to explode
What is the number of collisions of gaseous molecules equal to?
The number of particles. the more gaseous molecules there are inside a balloon the more frequently they will hit the walls, hence the higher the pressure
What is pressure proportional to?
at higher temperatures, things move faster and hit the walls of the container more
What is the number of collisions inversely proportional to?
if we took all the gas molecules and put it in our hands there would be more collisions as they occupy a smaller space. however if we opened up the volume to the whole room they would have to travel further to hit a wall so the number of collisions decrease
What does a bigger volume therefore mean?
a reduced pressure
What does the ideal gas law tell us?
PV = nRT
where R is the universal gas constant
tells us that equal volumes of gas at the same temperature or pressure have an equal number of molecules regardless of the type of gas it is
What does an ideal gas mean?
there are no interactive forces between the molecules.
with a gas, there is a huge distance between molecules. They are so far apart we can assme no real attractive or repulsive forces
Gases behave differently to other states
what is liquefaction?
The conversion of a solid or a gas to a liquid
How is liquefaction achieved from a gas?
A temperature decreases, Ek is removed.
Gas molecules move more slowly
Pressure decreases so molecules will move closer to each other
eventually molecules are so close, attractive forces predominate and causes gaseous particles to collapse into the liquid state
What is the critical temperature?
the last moment where you can turn a gas back into a liquid?
Above this temperature, no matter how much pressure you apply, you cannot turn it back into a liquid
How can critical temperature be an indication of the intermolecular forces between the molecules?
Anywhere over 5.2K (kelvin) we cannot get liquid helium however water can be heated to high temperatures and still turn into a liquid. This shows that water has strong intermolecular forces including H bonding so can still be converted into a liquid whereas at high temperatures it is harder to get He to form a liquid
What is an aerosol?
a liquid or solid drug dissolved in a volatile propellant (usually liquid under the pressured confines of a can) e.g. shaving gell, deodorant
How do aerosols work?
When you press down on the buttton it opens a valve and a small amount of the pressurised liquid, including the drug/active ingredient etc escapes
This opens up as a gas as soon as it reaches atmospheric pressure
Why were traditional propellants like CFC and NFC replaced?
Replaced by FC's and others as they were bad for the ozone layer
Why is the aerosol a liquid inside the canister?
The pressure inside the canister is higher than atmospheric pressure so molecules are forced closer.
This causes attractive forces to predominate and so the aerosol is a liquid.
As it moves into atmospheric pressure, molecules can move away from each other and are no longer under the effect of attractive forces, so move apart to form a gas
What is vapour pressure?
the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system
aka the tendency of the particles of a liquid to escape into the vapour phase.
High vapour pressue = high volatility of liquid
What is the theory behind vapour pressure?
All molecules are moving, some move faster than others.
e.g. water at 20 degrees C will have some molecules moving faster and others moving slower.
Faster moving molecules can escape into the air
What happens if a molecule from the liquid phase leaves?
The overall energy of the molecules which have been left behind, will decrease.
e.g. ethanol feels cool due to energy having escaped
What is the pressure that evaporated molecules exert called?
An equillibrium exists between the vapour pressure and the ____?
What happens if the actual vapour pressure is greater than the equilbirum pressure?
The vapour will have a tendency to escape
What occurs at equilibiumr?
The VP due to liquid molecules escape however there is no movement.
there is a dynamic equilbrium present, and molecules continue to be exchanged
What is vapour pressure proportional to?
decreased temperature decreases the equilbium pressure causing condensation to occur
what causes condensation?
A drop in the temperature causes equilibrium pressure to drop. Particles will move from the gas phase back into the liquid phase, causing condensation
What causes evaporation?
A raise in temperature causes vapour pressure to increase. more particles will move from the liuid phase into the vapour or gaseous phase, causing evporation
What is vapour pressure inversely proportional to?
Weaker intermolecular forces = higher vapour pressues.
Strong intermolecular forces = lower vapour pressure so will remain more as a liquid
What are the two types of solids?
crystalline and amorphous
what is crystalline?
a type of solid in which the structure is ordered e.g. grain of salt/sugar
what is amorpous
type of solid in which the structure has no form like plastic and glass
What are the differences between crystalline and amorphous solids?
Crystalline solids have a sharp defined melting point. Nothing hapens as you go up to that point but once it you hit the point it immediately melts
amorphous solids have a range of melting points. When you get close to the point, some molecules start melting.
What is the latent heat of fusion?
The energy absorbed when one mole of solid melts
What does increaseing the pressure do to the melting point of water?
it will increase the melting point of water,
Require a higher temperature to melt the water
What happens if you increase the pressure of the water?
Water particles will try to decrease the pressure and adapt.
Does liquid water have more pressure?
What is the heat of fusion required for?
to increase the intermolecular distances and to overcome the intermolecular forces of attraction
What is the relationship between hydrocarbon chain length and melting point?
The longer the hydrocarbon chain, the higher the melting point
This is due to longer chains having more bonding and thus more intermolecular (van der waal) forces capable of producing instantaneous dipoles
What is the relationship between melting point and aqueous solubility?
If the MP is too high the drug will not want to dissolve and thus will have a lower solubility
What does the behaviour of crystalline solids depend on?
The natural substance and nature of the crystal i.e. what the crystal is made up of
What does crystal habit refer to?
The shape of the crystal, whether its spherical etc.
What does amorphous mean?
what does polymorphism mean?
many different forms
can crystals exist in different forms?
What can most long chain organic compounds exist as?
polymorphs e.g. diamond and graphite
What are the differences between polymorphs?
One is often more stable than the other
They can have different solubilites
What is the relationship between stability of a polymorph and its solubility?
If its more stable, it will be less soluble as it will want to stay in the form it currently is in.
What is one problem with all states of matter over time?
It will revert to the most stable form which is sometimes the least soluble form
What is the relationship between solubility and shape?
Different shapes have different solubilities as some may dissolve faster or slower depending on the surface area availble for dissolution
The processing of a tablet can change the dosage of the drug. i.e. if turned into fine needles, the surface area and solubility etc will havechanged
what is theobromo oil?
a natural fat which has 4 polymorphisms
what is theobromo oil used for?
We want this to be solid for application and then melt in the body
Which polymorph of theobromo oil should we therefore use?
the polymorph that melts at 34.5 degreesC
How is the polymorph of theobromo oil which melts at 34.5 degrees different ?
the crystals are put together in a different way so when heated above 35 degrees, all the beta crystal nuclei are destroyed.
If heated to 33 degrees it is cool enough to pour and on cooling, will form the beta polymorph
What are liquid crystals in relation to states of matter?
they are the 4th state of matter and are relevant to pharmacy
What is a liquid crystal in terms of structure?
It is a liquid with structure. It can still move.
It gives rise to properties i.e. rotating the plane of polarised light
What are the phospholipids of our cell membranes made up of?
What is birefringence?
An optical quality of liquid crystals which have a refractive index that depends on the polarization and propagation direction of light.
It causes the double refraction phenomenon which allows light through even when it has previously been through a polariser
What is a polariser?
Something that filters light.
When unfiltered light is shone through a polarisoer, only photons oscillating in a certain direction will be let through.
What happens to light when shone through two polarisers at 90degrees to each other?
There shouldnt be any light seen, as no photons would be let through
How does a liquid crystal let through polarised light?
It bends and breaks the line of polarised light.
It will be shifted so that it goes through the second polariser
How can polarised light be used to detect crystalline and amorphous solids?
Crystals will let polarised light through, amorphous substances will not.
What happens to the cell membrane when you change the water concentration?
It may change the way the cell membrane arranges itself e.g. may change from a cubic structure to a discontinuous strcture.
How can a liquid crystal be useful in drug delivery?
We can create a drug delivery system where you load a liquid crystal with a drug. This can be injected into the skin in a laminar form, causing the drug to be stuck in the middle.
When the drug is required, we can use an ultrasound to pulse the skin and release the drug into your body