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Properties
associated with Ionic Bonding
·
Non-Directional
Bonding: Materials are plastic.
· Electrons are bound
to ion
cores: Electronic insulator; Transparent at low photon
energies (visible,
near IR). Absorbs
light in the ultra-violet
(6.5 eV).
· Ions have charges and can move
in the crystal at high temperatures: Ionic conductors at high temperatures.
· Ions vibrate about their equilibrium lattice positions and
can interact with light: Materials absorbs in the infrared
(IR) .
· Crystals
have high binding energies (eV per molecule) and, therefore,
have high melting points. Typical energies are:
KCl Ø 7.3 eV; AgBr ➢ 5.4eV; BaF2 Ø 17.3 eV
· The materials have different crystal
structures: KCl Ø Cubic
(NaCl); AgBr Ø Cubic (NaCl);
BaF2 Ø Cubic (CaF2,
Fluorite), and nearest neighbor distances: KCl Ø 0.314 nm; AgBr Ø 0.288 nm; BaF2 Ø 0.269 nm
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