19 - lattice energy Flashcards
lattice energy
the energy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions, exo
lattice energy pointers
. always gaseous ions
. always exothermic
lower lattice energy =
more stable ionic lattice (compared to its gaseous ions)
standard enthalpy change of atomisation
the enthalpy change when 1 mole of gaseous atoms is formed from its elements under standard conditions, endo
first electron affinity (EA1)
the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous ions with a single negative charge under standard condition, usually exo
EA1 notes
. change is from gaseous atoms to gaseous 1- atoms
. generally exo
second electron affinities (EA2)
the enthalpy change when 1 mole of electrons is added to 1 mole of gaeous 1- ions to form 1 mole of gaseous 2 - ions nder standard conditions, endo
electron affinity trends
more energy
. more nuclear charge
. less distance
. less shells
F IS ANOMALY
F (anomaly)’s electron affinity
. less than Cl
because
. small atomic radius
. high electron density
. more repulsion
. less attraction
<>H1 + <>H latt = <>H f
<>H latt = <>Hf - <>H1
for ionising metals
IE
for ionising non metals
EA
for Born-Haber cycles
. atomise metal
. ionise metal
. atomise non metal
. ionise non metal
born-haber cycle as energy level diagram
. up arrow = endo (atomise, ionise, atomise)
. down arrow = exo (ea, Hlatt, Hf)
factors affecting lattice energy values
. more ion size, less lattice energy
. more ionic charge, more lattice energy
ion polarisation
the distortion of the electron cloud of an anion by a neighbouring cation
more distortion when:
. small cation
. highly changred cation
polarising power
the ability of a cation to attract the electron cloud of an anion and distort it
degree of polarisation on an anion depends on
. charge density of cation
. ease with which anion can be polarised
anion more likely to be polarised if
. cation is small
. cation has 2+ or 3+ charge
. anion is large
. anion has 2- or 3- charge
ionic compounds have covalent character due to ion polarisation
thermal stability of group 2 carbonates and nitrates
. ionic radius increase down group
. polarisation degree decreases
. decreasing ease to weaken a C-O bond in carbonate
. stability increases down group
. decomp. temp. increases down group
. <>Hr increases down group
standard enthalpy change of solution
the energy absorbed or released when 1 mold of an ionic solid dissolves in sufficient water to form a very dilute solution under standard conditions
. aq - large amt. of water used
. can be exo or endo
. exo/ small endo = soluble
. endo = insoluble
ion dipole bonds
the bond formed between an ion and polar compound such as water
. negative end of dipole bonds with positive ion
. positive end of dipole bonds with negative ion
standard enthalpy change of hydration
the enthalpy change when 1 mole if a specified gaseous ion dissolved in sufficient water to form a very dilute solution under standard conditions
. always exo
. more charge, more exo
. less radius, more exo
. more strong ion dipole attraction, more exo
<>H sol + <>H latt = <>H hyd
group 2 sulfate solublilty decreases as
radius of metal ion increases
group 2 sulfate solublilty decreases as down group, why?
. decreasing <>H hyd
. less decreasing <>H latt (due to large sulfate ion)
. <>H sol gets more endo
thus solubility decreases
