The stability of ionic solid is measured in terms of its lattice energy. Lattice energy is defined as the energy released when one mole of an ionic crystal is formed from one mole of gaseous positive and one mole of gaseous negative ions, when these are separated from each other by infinite distance. Greater the value of lattice energy, more stability in the ionic solid.
Na+ (g) + Cl− (g) → NaCl (s)
The lattice energy of the sodium chloride is -782 KJ/mol. The negative sign indicates that the process is exothermic and that of the system is lowered as the solid is formed.
Na+ (g) + Cl− (g) → NaCl (s)
The lattice energy of the sodium chloride is -782 KJ/mol. The negative sign indicates that the process is exothermic and that of the system is lowered as the solid is formed.Factors affecting lattice energy:
The force of attraction between oppositely charged ion governed by
- Their Ionic Radii
- The charge on the ions
It is given by the equation F= q1q2/r2
where q1 and q2 are the point charges seperated by distance r in the vacuum.
It is observed that if the radii of the ions are large, the force of attraction will be less. This is better illustrated if we compare the stability of NaCl and CsCl. The force of attraction between the large Cs+ ions and Cl- ions will be less than that between the smaller Na+ ions and Cl- ions. As a result, CsCl is less stable than NaCl. We may say that the stability of an ionic solid increase with decrease interionic distance for crystals with similar ionic charges.
The role played by the charges on the ions demonstrated if we compare the lattice energy of BaO and NaCl, since both have very similar inter nuclear distance (NaCl=281 pm and Ba=277 pm). Since Ba consist of doubly charged Ba2+ and O2- ions, the force of attraction is much large than that in NaCl which contains singly charged ions. Hence BaO is more stable than NaCl. The stability of ionic charge for crystal with similar inter ionic distance.
SOME LATTICE ENERGY OF COMPOUNDS
It is observed that if the radii of the ions are large, the force of attraction will be less. This is better illustrated if we compare the stability of NaCl and CsCl. The force of attraction between the large Cs+ ions and Cl- ions will be less than that between the smaller Na+ ions and Cl- ions. As a result, CsCl is less stable than NaCl. We may say that the stability of an ionic solid increase with decrease interionic distance for crystals with similar ionic charges.
The role played by the charges on the ions demonstrated if we compare the lattice energy of BaO and NaCl, since both have very similar inter nuclear distance (NaCl=281 pm and Ba=277 pm). Since Ba consist of doubly charged Ba2+ and O2- ions, the force of attraction is much large than that in NaCl which contains singly charged ions. Hence BaO is more stable than NaCl. The stability of ionic charge for crystal with similar inter ionic distance.
SOME LATTICE ENERGY OF COMPOUNDS
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| Lattice Energy of chemical compounds |
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