Unformatted text preview: nergy The
The highest
electron affinity The Ionic Bond
Formation
Formation of Ionic Compounds are very exothermic
exothermic
reactions! ∆H < 0 2Na(s) + Cl2 (g) → 2 NaCl(s) ∆H o = - 410.9kJ/mole
f Heat of formation
of an ionic
compound is very
negative Mainly due to
lattice energy Lattice
Lattice energy
Lattice energy :
The energy required to
completely separate 1 mole
of a solid ionic compound
into gaseous ions. NaCl(s) → Na + (g) + Cl- (g)
∆H lattice = +788 kJ/mole
Endothermic Because the ions are strongly attracted to one another
in the lattice. Lattice Energy (Electrostatic Attraction)
Lattice energy (E): much depends on the charges of
charges
ions, the sizes of ions and their arrangement in solid
sizes
arrangement
Q+ : the charge on the cation Q+ ⋅ Q−
E=k
r Q- : the charge on the anion
r : the distance between the ions
Compound Lattice energy (E) lattice energy MgF2
MgO 2957 LiF
LiCl 1036
853 3938 Q= +2,-1
Q= +2,-2 increases as Q increase
increases as r decreases r(F) < r(Cl) Lattice Energy ↓
↓
↓
↓ Larger ion, less
lattice
lattice energy higher charge, higher
lattice energy The
The Covalent bond
• Covalent bond: the force that holds two atoms together
as both nuclei are attracting the same pair of valence
nuclei
same
electrons.
“Shared” the pair of
valence electrons by the
two
two atoms-- “octet”
F
7e- + F FF 7e- 8e- 8e- share 1 pair of e (2e) single bond (—) Cl - Cl share 2 pairs of e (4e) double bond (=) O=O share 3 pairs of e (6e) triple bond (≡) N≡N The
The Covalent bond--- Bond length
bond--- Bond length:
length:
single bond (—)
is the longest
the Bond strength:
triple bond (≡)
is the strongest Polar Covalent Bond
Polar covalent bond (or polar bond): a covalent bond
with greater electron density around one of the two atoms
electron poo...
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- Fall '14
- Electrons, Chemical bond, Lattice Energy
-
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