thermodynamics

lattice enthalpy of dissociation = when 1 mole of a solid ionic lattice is separated into its constituent gaseous ions lattice enthalpy of dissociation = when 1 mole of a solid ionic lattice is formed from its gaseous ions lattice enthalpy measures strength of ionic bonding

• ion size • ion charge • charge density = ion charge/ion size • the smallest ions with the biggest size have the highest charge density • the higher the charge density, the stronger the electrostatic attractions between oppositely charged ions

for negative ions: • size increases as charge increases because more e- than protons = • weaker electrostatic attraction between outer e- and positive nucleus • also increased e- repulsion between inner e- and added e- = bigger ionic radius for positive ions: • size decreases as charge increases because less outer e- than protons • stronger electrostatic attraction between positive nucleus and outer e- = decreased ionic radius

O2- ions smaller and has bigger charge than Cl- ion oxide ions have higher charge density than chloride ions stronger electrostatic attraction between Mg2+ and O2- tha between Mg2+ and Cl- more energy released when Mg2+ and O2- form ionic lattice than when Mg2+ and Cl- form ionic lattice MgO therefore has more exothermic lattice enthalpy of formation

enthalpy change for the formation of 1 mole of gaseous atoms from its element in its standard state e.g 1/2 Br2 (l) → Br (g)

enthalpy change when 1 mole of covalent bonds is broken under standard conditions in the gaseous state e.g F2(g) →2F (g) bond dissociation enthalpy for diatomic molecules is twice the enthalpy of atomisation

enthalpy change when 1 mole of gaseous atoms form 1 mole of 1- ions e.g. F(g) + 1e- →F- (g)

it is endothermic due to the repulsion between 1- ion and the negative e- being added

100% ionic bonding with 0% covalent character both ions are perfect spheres with no distortion

positve ions that are small and/or highly charged are good at polarising negative ions negative ions that are large and/or highly charged are easier to be polarised polarisation of negative ion results in ionic bonding having covalent character the larger the % diff between theoretical lattice enthalpy (which assumes 100% ionic bonding) and experimental lattice, the the more covalent character the ionic solid has due to more distorted,polarised negatice ions.

begin with elements in their standard states (these have energy zero) ↑ = positive enthalpy (Endothermic) ↓ = negative enthalpy (Exothermic) remember all enthalpies must be multiplied by the number of moles in the orginal chemical equation lattice enthalpy of formation of aluminium oxide given by the equation 2Al3+ (g) + 3O2-(g) → Al2O3 (s)

when 1 mole of a solid ionic lattice dissolves completely in large volume of water so that the dissolved aqueous ions are far enough apart to not interact e.g NaCl (s) → Na+(aq) + Cl-(aq) ΔsolHθ = ΔLdHθ +Σ ΔhydHθ​(ions) ​

ion size and ion charge (charge density) the bigger the charge and the smaller the size = the higher the charge density = ion attracts 𝛿+ H/ 𝛿- O of water molecule more strongly = more exothermic hydration enthalpy

enthalpy change when 1 mole of e- is removed from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

the enthalpy of dissociation is bery endothermic = strong electrostatic attraction between Ca2+ and O2- ions = large amount of energy required to form Ca2+ (aq) and O2-(aq)

covalent chracter reduces the MP due to weaker IMF covalent bonds are stronger than ionic bonds so lattice enthalpy of formation will be more exothermic (more negative). lattice enthalpy of dissociation will be more endothermic (bigger)