Chemistry (intermolecular forces) term 3 week 2 test

metallic

attractive forces act between positive metal cations and the delocalised electrons. this is non-directional bond.

ionic

attractive forces act between oppositely charged positive (cation) and negative (anions) ions.

covalent

attractive force between atoms that share electrons

molecular: share electrons to form discrete molecules

network: share electrons to form an extended 3D lattice

factors that affect the strength of metallic bonds

the number of protons (the more protons the stronger the bond)

number of delocalised electrons per atom (the more the stronger the bond)

the size of the cation (the smaller the cation the stronger the bond)

factors affecting the strength of the ionic bond

in ionic bonds, charge and distance are two factors affect strength of bond. greater the charge on ions and smaller the distance between ions, greater the attraction between ions, therefore greater strength of bond.

intramolecular forces

refers to the forces within the molecule that are holding atoms together to form a molecule

intermolecular forces

refers to the force of attraction acting between molecules which holds many molecules together.

properties intermolecular forces influence

temperature change, at which a change of state occurs

ease of evaporation of particles and subsequent vapour pressure and type of degree of dissolving in different solvents.

change of state property

to change state energy needs to be added or removed from particles, changing their motion (kinetic energy) and distance between particles (potential energy).

melting point is the temp compound is changing between a solid and liquid.attractive forces are overcome so particles can slide past each other.

boiling point is temp which compound is changing between liquid and gas. attractive forces are overcome so particles spread apart and move independently.

stronger the intermolecular forces between the molecules the more energy required to break forces and the higher the melting and B.P.

Evaporation property

occurs at any temp not B.P

process of changing from liquid to gas

within compound particles moving and have a range of kinetic energies.

the particles at the surface with the most energy more likely to escape and change from L to G

slower moving particles remain in the liquid so the average KE drops, resulting in a drop in temp of the evaporating solution.

compounds with weak intermolecular forces evaporate faster

vapour pressure property

due to evaporation gas particles build up above liquid

both evaporation and condensation are occurring and reach equilibrium

pressure exerted by gas colliding with the container is called vapour pressure

volatile liquids evaporate readily so have high vapour pressures

particles evaporate easily if attractive forces are weak

increasing the temp of liquids increases number of particles with enough energy to escape, increasing vapour pressure

boiling point property

heating provides particles throughout liquid with sufficient energy to change from liquid to gas

bubbles (gas/vapour) forms throughout the liquid

temp at which this occurs is called the boiling temp

boiling occurs when the vapour pressure = atmospheric pressure

solubility property

solubility describes the amount of solute that can dissolve in a solvent

if a solute dissolves its solubility is above 0.1 moles dissolved per litre

a substance is considered insoluble if less than 0.1 moles dissolve per litre

slightly soluble 0.01-0.1 moles dissolved per litre

to dissolve attractive forces solute-solute and solvent have to be broken and new attractive forces solute-solvent

if solute-solute or solvent-solvent attractive forces are too strong (greater than solute-solvent) the dissolving will not occur

“like dissolves like” is a simplified form of the idea that similar forces need to form to overcome existing forces.

molecule shapes

linear

tetrahedral

pyramidal

bent

tragical planar

polarity

a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. polarity occurs due to uneven distribution of electrons

non-polar bonds

occur between identical atoms in a molecule so that even sharing of electrons

no net dipole, even distribution of electrons

polar molecule

has a net dipole

uneven charge distribution on the molecule resulting in a region of partial positive charge separated from a region of partial negative charge.

asymmetrical molecule

individual bond dipoles that add as vectors to give a net dipoleype of intermolect

type of intermolecular force: dispersion

occur between all molecules

only one force present between non-polar molecules so this is it.

attractive due to formation of temporary dipoles(region of charge separation) that occur because of constant movement of electrons, at any one time electrons may be grouped together to create a more negative region leaving a mote positive region elsewhere.

type of intermolecular force: dipole-dipole

occur between polar molecules (molecules with a net-dipole) due to the attraction between the partial positive and partial negative regions of neighbouring molecules.

occurs in molecules with uneven sharing of electrons in bond (polar bond) and asymmetrical shape

type of intermolecular bonding: hydrogen

stronger type of dipole force than expected. occur between O-H, or N-H, or F-H and other polar molecules including N/F/O with a lone pair of electrons.

an attraction occurs between the strong δ⁺ H formed on one molecule (this is due to the high electronegativity of O, N, F) and the lone pair of electrons on the neighbouring molecule of an N/F/O atom.

O/N/F are atoms that have a very high electronegativities and a small radii so that a high charge density occurs making the atoms more polar than expected.

Type of intermolecular force: dipole-ion

a polar molecule has partial charges that are attracted to the opposite charges of ions. an ion differs to a polar molecule because it is completely charged due to loss/gain of electrons. A polar molecule is neutral but has regions of partial charges.