Lattice enthalpy Flashcards
1
Q
Define lattice enthalpy
A
- measure of strength of electrostatic attraction
- between oppositely charged ions
- in ionic compound
- indication of strength of ionic bond
- higher LE of an ionic lattice : higher ionic bond strength, more stable
2
Q
Factors affect LE
A
- Ionic size
2. Ionic charge
3
Q
Ionic size
A
- smaller ions (smaller dist between ions)
- greater electrostatic attraction btwn them
- greater LE
- LE: NaF > NaCl > NaBr > NaI
- Ionic size: F- < Cl- < Br- < I-
4
Q
Effect of ionic charge
A
- greater ionic charge of cations ( +3 > +2 > +1)
- greater attraction btwn them
- higher LE
- more stable
- e.g. LE: MgO > MgCl2 > NaCl
5
Q
Significance of LE
A
- higher LE, ionic compound more stable
- more exothermic lattice energy, ionic compound more stable
6
Q
Assumptions made in calculating LE of ionic compound
A
- Made up of ions only
- Ions are spherical
- Electric charges in ions distributed uniformly
- Only force experienced of ions is electostatic (pure ionic bonding)
5 Cations and anions are in contact with each other and with electrostatic interactions in btwn
7
Q
Theoretical value
A
- pure ionic boning
- ions uniformly charged
- perfect spheres
8
Q
Theoretical vs experimental (Large discrepancy)
A
- crystal lattice does not consist of separate spherical ions
- charge distribution not uniform
- not completely ionic in character, covalent character existing in ionic crystal
- greater discrepancy, greater covalent character of bond
9
Q
Theoretical vs experimental (Small discrepancy)
A
- structure closely resembles model for pure ionic bonding
- ions spherical, charge distribution uniform
- strong ionic character
10
Q
Pure ionic compound
A
- ionic compound formed by
- complete electron transfer frm a metallic atom to a non-metallic atom
