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What are intermolecular forces?

Forces between molecules that decide how molecules behave with each other

These decide the state of matter


What are the two main kinds of intermolecular forces?

Repulsive forces which push molecules apart and attractive forces which bring molecules together

These are balanced

The balance of these dictate what state the substance is in


What is the role of intramolecular forces?

They Decide what is inside molecules
decide whether a suspension or emulsion is stabilised


What is a suspension?

A substance in which there are solid particles suspended in a liquid vehicle


What is the importance of suspensions?

We need to be able to stabilise suspensions in order to produce a pharmaceutical product with an accurate dose. If its not stabilised the dose will be inaccurate


How can the stabilisation be controlled?

By controlling the forces


What is in vivo?

in the body


What is vitro?

out of the boy (usually glassware)


how can a solid drug be absorbed and travel around the body?

It must first be dissolved in solution


Where do repulsive forces originate from?

Every molecule or atom has an electron cloud on the outside, These are negatively charged so if you bring them together they will repel


What is the relationship of repulsive forces and distance?

Repulsive forces increase exponentially with decreased intermolecular distance.

Like a magnet, the closer you bring them together, the harder they will push apart


What is the importance of repulsive forces?

They are positive energy (see graph)
Bringing atoms closer together increases repulsive force

This stops molecules from crashing into each other


What do attractive forces allow molecules to do?


It makes matter coherent.


Where do attractive forces originate?

Although electron clouds of an atom are negative, the nuclei are positive so there will be some attraction between molecules due to some positive parts and some negative parts


What does the attractive forces curve look like?

It is similar, but opposite to the repulsive curve


What is the relationship between attractive forces and distance?

As molecules are closer, attraction is stronger


Which charges cause attraction?

Opposite charges.


Are intermolecular forces stronger or weaker than intramolecular forces?



What are intramolecular forces?

Forces within molecules.


What are intramolecular forces stronger than intermolecular forces?

Otherwise the molecule would break apart and change what it is.


How much stronger are intramolecular forces compared to intermolecular forces?

about 10x stronger


What are the common names of intermolecular forces?

Van der waal forces - be3tween electron clouds in opposite molecules

Ion dipole forces

ion induced dipole forces

Hydrogen bonding


What are van der waal forces?

A loosely defined set of forces involving polar molecules in which polar molecues have permanent dipoles e.g. C covalently bonded to O. O is more electronegative so pulls the electrons towards itself. This creates a polar bond, i.e. a permanent dipole


What is a polar molecule?

A molecule in which there is an uneven sharing of electrons between atoms due to some atoms being more electronegative than others


What is an ion dipole force?

The type of force Where a dipole created by polar bonds is attracted to an ion due to opposite charges


What is an induced dipole force?

When a molecule which initially has no charge or dipole is induced by a new ion or dipole molecule by placing it next to it and thereby causing electrons to repel. This results in the first molecule having an induced dipole and will therefore be attracted to the 'new' ion or dipole


What is hydrogen bonding?

When H is bonded to either F, O or N which are very electronegative. This H-F molecule can then bond strongly to other H-F molecules. The bond between each individual molecule is the hydrogen bond


How can an induced dipole force be used to our advantage

I-I is a non polar molecule, but if we bring another molecule closer we can induce a dipole as electrons in the first molecule are repelled from the side closest to the second molecule.
This makes the left side negative and the right side positive resulting in the induced dipole.

I2 dissolves poorly in water, but if you add KI, it will dissociate in water to form I-, which can set up an induced dipole when within close proximity to I2. This will increase the solubility of I2 as it will more happily dissolve as a I3- ion


Why is the dissolution of Iodine important?

Iodine has antibacterial and antifungal properties,

It is also useful in a radioactive accident


How can Iodine help in a radioactive accident?

Our thyroid hormones contain I in it.
In the event of a major nuclear break down, we can take I2 tablets so our bodies can be saturated with Good I2 (as opposed to radioactive I2) We therefore will not take up radioactive I2


How do intermolecular forces determine state of matter?

If intermolecular forces are rigid this results in a solid,

If more movement is allowed between molecules, this results in a liquid