Energy involved in chemical bonding

1. ENERGY INVOLVED IN
BONDING

2. FORMATION OF SODIUM CHLORIDE

3. Formation of NaCl
Na(s)
NaCl (s)
Na(g)
Na+
(g)
Cl-
(g)
Cl(g)
Cl2 (g)

4. Steps Involved
1. Elements (standard state) converted into gaseous atoms
2. Losing or gaining electrons to form cations and anions
3. Combining gaseous anions and cations to form a solid ionic
compound
4. Combining all the steps
Let’s consider:

5. LATTICE ENERGIES
lattice energy: energy required to break ionic bonds and
sublime (always positive).

6. Step 1: Convert from Solid to Gas
• The standard enthalpy change of atomisation is the ΔH required
to produce one mole of gaseous atoms (enthalpy of Sublimation -
from solid to gas)

7. Step 1: Convert from Solid to Gas
• The standard enthalpy change of atomisation is the ΔH required to produce
one mole of gaseous atoms (enthalpy of Sublimation - from solid to gas). NOTE:
for diatomic gaseous elements, ΔHo
at is equal to half the bond energy
(enthalpy)

8. Becoming cations
• Ionization energy
• Enthalpy change for one mole of a gaseous element or cation to lose
electrons to form a mole of positively charged gaseous ions

9. Step 2: Formation of gaseous ions
• Electron Affinity
• Enthalpy change when one mole of gaseous atoms or anions gains electrons
to form a mole of negatively charged gaseous ions.
• For most atoms = exothermic, but gaining a 2nd
electron is endothermic due
to the repulsion between the anion and the electron

10. Lattice Enthalpy
• Energy required to convert one mole of the solid compound into
gaseous ions.
• It is highly endothermic
• We cannot directly calculate ΔHo
lat , but values are obtained indirectly
through Hess’s law for the formation of the ionic compound
• We will use the reverse of this lattice energy equation to find the
lattice energy

11. Introduction to the Born – Haber cycle

12. EXAMPLES

13. Calculations
• Calculate the lattice energy of NaCl(s) using the
following: (kJmol-1
)
ΔHf° = Δ Hs°+ Δ HIE°+ Δ Ha°+ Δ Hea°- U

14. • Ionisation energy (first and second)
• Electron affinity (first and second)
• Dissociation energy
• Sublimation energy
• Enthalpy of formation
• Lattice energy
• Enthalphy of atomisation

15. • Calculate the enthalpy of formation of Magnesium Floride given the
following information

18. • Calculate the lattice energy of Sodium oxide given the following
information
• Heat of formation of Na2O = -414 kJ/mol
• Atomization energy of sodium = +107 kJ/mol
• Ionization energy of sodium = + 496 kJ/mol
• Atomization energy of oxygen = +498 kJ/mol
• 1st electron affinity for oxygen = -141 kJ/mol
• second electron affinity for oxygen = 844 kJ/mol