Comparing Lattice enthalpies Flashcards
1
Q
What are the 3 things that are used to calculate the theoretical lattice enthalpy?
A
- Geometry of the ionic solid
- Charge of ions
- Distance between ions
2
Q
Why might there be a different theoretical and experimental lattice enthalpy?
A
The theoretical value is calculated assuming that there are only electrostatic forces of attraction between the cations and anions.
A higher experimental value suggests there is some covalent character present.
3
Q
Covalent character in ZnS compared to NaCl?
A
- Zn2+ smaller ion with greater charge than Na+
- Zn2+ attracts electron density towards them, distorting the electron cloud
- Bonding becomes slightly covalent
- Sulfide ions are larger than chloride ions and have a greater negative charge
- So electron cloud more easily distorted
4
Q
What are the 2 KEY factors that affect lattice enthalpy?
A
- Charge
- Radius of ions
5
Q
How does ionic radius affect lattice enthalpy?
A
- As ionic radius of ion increases
- Lattice enthalpy becomes less exothermic
- Charge of ions more spread out when ion is larger
- And ions are further apart in lattice
- So electrostatic forces of attraction between opposite charged ions in lattice are weaker
6
Q
How does ionic charge affect lattice enthalpy?
A
- As charge increases
- Becomes more exothermic
- Greater electron density
- ## Higher electrostatic forces of attraction between oppositely charged ions in lattice
