CAMBRIDGE
INTERNATIONAL A2
LEVEL CHEMISTRY
(9701) PHYSICAL
CHEMISTRY NOTES
, CHAPTER 19: LATTICE ENERGY
Definitions:
- Enthalpy of atomization
o enthalpy change when 1 mole of gaseous atoms is formed from the element in its
standard state
- Enthalpy of formation
o Enthalpy change when 1 mole of a compounds is formed from its elements
- Lattice energy
o Energy change when 1 mole of a solid lattice is formed from its gaseous ions
st
- 1 ionization energy
o Energy required to remove 1 mole of electrons from 1 mol of atoms to form 1 mol of
gaseous +1 ions
- Bond energy
o The energy required to break one mole of a particular bond in the gaseous state
- Electron affinity
o Enthalpy change when 1 mol of electrons is added to 1 mole of atoms to form 1 mol of
gaseous -1 ions
- Enthalpy of hydration
o Enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to form a very
dilute solution
- Enthalpy of solution
o Enthalpy change when 1 mol of an ionic solid dissolves in sufficient water to form a very
dilute solution
,Trend of electron affinity (EA):
- Cl(g) + e- Cl-(g)
- Going down a group, EA becomes less exothermic/ more endothermic:
o Nuclear charge increases
o The distance between the outermost electrons and the nucleus increases
o Shielding effect increases
o Hence, the attraction for the incoming electron decreases
- 2 and 3rd EA are always endothermic
nd
o An electron is being added to a negatively-charged ion
Lattice energy:
- Coulomb’s Law:
-
-
- Higher charge density – stronger electrostatic forces between ions – more exothermic lattice –
more energy is released during the formation of the ionic bond….. and vice versa
- Increasing lattice energy:
Recap (Chap 6: enthalpy changes):
-
Born-Haber cycles:
- Describe the direct and indirect routes
of forming an ionic compound
o Element
o Gaseous ions
o Final ionic compound
, - Another way to look at the Born-Haber cycle
Factors affecting enthalpy change of hydration, ΔH∘hyd:
- Force of attraction,
Predicting enthalpy of hydration: Na+ vs Li-:
- Observation: less energy is released when sodium ions are hydrated (390 kJ mol -1) than when
lithium ions are hydrated (499 kJ mol-1)
INTERNATIONAL A2
LEVEL CHEMISTRY
(9701) PHYSICAL
CHEMISTRY NOTES
, CHAPTER 19: LATTICE ENERGY
Definitions:
- Enthalpy of atomization
o enthalpy change when 1 mole of gaseous atoms is formed from the element in its
standard state
- Enthalpy of formation
o Enthalpy change when 1 mole of a compounds is formed from its elements
- Lattice energy
o Energy change when 1 mole of a solid lattice is formed from its gaseous ions
st
- 1 ionization energy
o Energy required to remove 1 mole of electrons from 1 mol of atoms to form 1 mol of
gaseous +1 ions
- Bond energy
o The energy required to break one mole of a particular bond in the gaseous state
- Electron affinity
o Enthalpy change when 1 mol of electrons is added to 1 mole of atoms to form 1 mol of
gaseous -1 ions
- Enthalpy of hydration
o Enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to form a very
dilute solution
- Enthalpy of solution
o Enthalpy change when 1 mol of an ionic solid dissolves in sufficient water to form a very
dilute solution
,Trend of electron affinity (EA):
- Cl(g) + e- Cl-(g)
- Going down a group, EA becomes less exothermic/ more endothermic:
o Nuclear charge increases
o The distance between the outermost electrons and the nucleus increases
o Shielding effect increases
o Hence, the attraction for the incoming electron decreases
- 2 and 3rd EA are always endothermic
nd
o An electron is being added to a negatively-charged ion
Lattice energy:
- Coulomb’s Law:
-
-
- Higher charge density – stronger electrostatic forces between ions – more exothermic lattice –
more energy is released during the formation of the ionic bond….. and vice versa
- Increasing lattice energy:
Recap (Chap 6: enthalpy changes):
-
Born-Haber cycles:
- Describe the direct and indirect routes
of forming an ionic compound
o Element
o Gaseous ions
o Final ionic compound
, - Another way to look at the Born-Haber cycle
Factors affecting enthalpy change of hydration, ΔH∘hyd:
- Force of attraction,
Predicting enthalpy of hydration: Na+ vs Li-:
- Observation: less energy is released when sodium ions are hydrated (390 kJ mol -1) than when
lithium ions are hydrated (499 kJ mol-1)
