Intermolecular forces/ Electronegativity/ Polarity

INTERMOLECULAR FORCES

3 types. Hydrogen bonding, Van der Waals forces, Permanent dipole-dipole forces.

Dipole to dipole interactions

Delta negative & delta positive attract eachother. Favourable dipole interactions. Sometimes there are two delta positive or two delta negative interacting, which we call unfavourable dipole interactions.

Van der Waals forces/ London dispersion forces

Electrons move randomly and therefore, for split seconds, one side of an atom’s electron shells may have more than the other. This creates two delta dipoles inside of the atom itself (instantaneous dipoles.) If another atom approaches, these dipoles will influence it (induced dipoles.)

Hydrogen bonding

Two things must be true for hydrogen bonding to occur:

• Must contain a hydrogen bonded to an electronegative element (oxygen, nitrogen, fluorine.)

• Must have another element with a lone pair of electrons

Because of the intensity of the electronegative elements, the hydrogen’s positive nucleus becomes slightly exposed. This allows the lone pair of negative electrons to be attracted to it and form an intermolecular force.

Order of strength (strongest to weakest):

• Hydrogen bonding

• Dipole to dipole

• Van der Waals

ELECTRONEGATIVITY

Electronegativity is an atom’s ability to attract shared electrons towards itself in a bond. If a more electronegative element is paired with an electropositive one, we call this an ionic bond, as the electronegative element gets such a large share that they basically transfer. If not we call it a covalent bond.

Features that make elements electronegative:

• Being small (few electron shells between the nucleus and shared electrons causes a stronger pull.)

• Being highly positively charged for their size

POLARITY