4. Types of Bonding/Intermolecular Forces

What are ions held together by

strong coulombic attractions

the closer the ion and dipole…

stronger the attraction

van der waals forces functions

• organic reactions between molecules

• how drugs may be formulated

• interactions between drugs and targets

types of van der waals forces

• dipole/dipole

• dipole/induced dipole

• induced dipole/induced dipole

whats a dipole/dipole attraction

when a polar molecule encounters another polar molecule, the positive end of one is attracted to the negative end of the other

extreme form of dipole/dipole interaction

hydrogen bonding

the higher the molecular mass…

the larger the electron cloud and the greater the polarizability

what is refractive index

when light passes through substances slower than it does through a vaccum

how does refractive index work

the light energy absorbed causes the waves to shorten and the speed to reduce

what is refraction

If light strikes the surface at an angle, it bends towards the perpendicular line of the surface

whats refraction measured by

the refractive index

2 refractive index variables

• wavelength of light

• temp

whats used to determine the refractive index

refractometer

what can a refractive index do?

• identify a substance

• be a measure of purity

• determine concentration of one substance dissolved in another

What is polarization?

A property of molecules that describes how electron distribution and bond dipoles affect molecular behaviour.

What is a dipole moment?

The vector sum of individual bond dipoles in a molecule indicating its polarity.

What does the dielectric constant measure?

A molecule's ability to resist charge separation

What are protic solvents?

Solvents that possess acidic protons

What do protic solvents often have?

High dielectric constants

What is the inductive effect?

The influence of electron distribution in sigma bonds caused by polarizing species.

What is the molecular dipole moment?

the vector sum of its individual bond dipoles

Examples of molecules that have dipole moments greater than 0

water and ammonia

what is the molecule regarded as if the dielectric constant is less than 5

non polar

if the dielectric constant falls between 5 - 15 what it is considered

semi polar

crystalline properties

narrow m.p range

well defined faces & edges

fracture or cleave under pressure

depends on orientation of particles

amorphous

• broad m.p range

• curved surfaces, globular

• yield n flow under pressure

why are amorphous materials less thermodynamically stable than crystalline forms

they have very high viscosities

what are pharmaceutical uses of amorphous solids (2)

• active ingredient as its more soluble

• additives

what is crystallisation?

production of a single component crystal

crystallisation process

• supersaturation

• formation of crystal nuclei

• crystal growth around the nuclei

what is supersaturation

formation of a solution containing more dissolved solute than in a saturated solution at max solubility

how can supersaturated solutions be obtained

• cooling of a saturated solution

• evaporation

• chemical reaction