Summary EDEXCEL A LEVEL CHEMISTRY UNIT 13 ENERGETICS II NOTES

13.1.1 IONIC BONDING & STRUCTURES
29 September 2021
19:57
Lattice - Regular 3D arrangement of atoms or ions in a crystal.
Ionic bonding - Electrostatic force of attraction between oppositely charged ions in a
lattice.




13.1.2 ENERGY CHANGES & IONIC BONDING
29 September 2021
20:07
Standard enthalpy change of formation, ΔfH* - Enthalpy change when 1 mole of a
substance is formed from its constituent elements in standard states under standard
conditions.

, 13.1.3 ENTHALPY CHANGES WHEN IONS
FORM
29 September 2021
20:12
Standard enthalpy change of atomisation, ΔatH
 Enthalpy change when 1 mole of gaseous atoms are formed from the element
in its standard state, under standard conditions.




1st electron affinity, Δe1H
 Enthalpy change when 1 mole of gaseous atoms gain 1 mole of electrons to
form 1 mole of 1- gaseous ions, under standard conditions.
Adding first electron is exothermic for non-metals, but others are endothermic.
 Electrostatic force of attraction to gain electron.
 After first electron, becomes negatively charged, and so repels 2nd electron.




Ionic lattices are held together by a net force of oppositely charged ions.
When gaseous ions combine to form a lattice, energy is released.
Standard lattice energy, ΔleH*
 Enthalpy change when 1 mole of an ionic substance is formed from its
constituent gaseous ions, under standard conditions.
Lattice energy is negative as forming lattice is exothermic.
 The more negative, the stronger the ionic lattice.
If ions have smaller radii and have larger charges, higher charge density and can also
pack closer together if smaller.
 Stronger electrostatic forces between ions, resulting in a more exothermic
lattice enthalpy.