Download IONIC BONDS MAIN GROUP CHEMISTRY

IONIC BONDS
MAIN GROUP CHEMISTRY
Periodicity of Properties
Main Group Chemistry
IONIC BONDS
IONIC SOLIDS
• Cation + Anion  Ionic Bond
• The solid that forms is an ionic solid with a
continuous network of cations surrounded
by anions and anions surrounded by
cations.
• The formation of ionic bonds is driven by
favorable energy considerations: this is
illustrated by the Born-Haber cycle.
Born-Haber Cycle (Fig 6.8)
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Start with elemental K and F2 (p 215)
K(s)  K(g)
Sublimation energy > 0
K(g)  K+(g) + eEi > 0
½ F2(g)  F(g) Dissociation energy > 0
F(g) + e-  F-(g)
Eea < 0
K+(g) + F-(g)  KF(s) - Lattice energy
Sum all of these rxns to get energy for
K(s) + ½ F2(g)  KF(s)
-562 kJ/mol
Lattice Energy, U
• KF(s)  K+(g) + F-(g)
U>0
• Electrostatic attraction between Cation
and Anion.
• Table 6.3
ALKALI METALS (1A)
• Valence electron config: ns1
• This single s electron is easily lost to form +1
cations. Therefore, these elements have low Ei,
are very strong reducing agents (recall Activity
Series), metallic, very reactive so they are not
found in nature in the elemental form.
• Reduction of metal chlorides yield commercial
metals.
• Table 6.4
RXNS OF 1A METALS
• Reactivity of 1A metals increases as you
go down group.
• + halogen  ionic solid metal halide salt
• + H2  metal hydride
• + N2  metal nitride
• + O2  metal oxide, peroxide, superoxide.
Note these oxides + water  base
• + water  H2 + metal hydroxide (base)
ALKALINE EARTH METALS (2A)
• Valence electron config: ns2
• These s electrons are easily lost to form +2
cations. Therefore, these elements have low Ei,
are very strong reducing agents (recall Activity
Series), metallic, very reactive so they are not
found in nature in the elemental form.
• Reduction of metal salts yield commercial metals
• Table 6.5
RXNS OF 2A METALS
• Reactivity of 2A metals increases as you
go down group. These reactions are
similar to the 1A metals but rxns are less
vigorous.
• + H2 or N2  metal hydride or nitride
• + O2  metal oxide, peroxide, superoxide.
Note these oxides + water  base
• + water  H2 + metal hydroxide (base)
GROUP 3A ELEMENTS
• Valence electron config: ns2 np
• These s and p electrons are lost to form
+3 cations. Therefore, these elements
have low Ei, are reducing agents, metallic
except for B.
• Table 6.6
• Forms halides, oxides, nitrides.
• Reacts with acid and base to form H2
HALOGENS (7A)
• Valence electron config: ns2 np5
• These elements readily accept electrons.
Therefore, they have high Ei, very
negative Eea, are very strong oxidizing
agents, nonmetals and exist as diatomics,
X2.
• Oxidation of anions yield commercial
metals
• Table 6.7
REACTIONS OF HALOGENS
• Reactivity of 7A nonmetals decreases as
you go down group.
• + metal  ionic solid metal halide salt
• + H2  hydrogen halide (acid in water)
• + Y2  XY
• + O2  nonmetal oxides. Note these
oxides + water  acid
• + water  acid
NOBLE GASES (8A)
• Valence electron config: ns2 np6
• These elements are unreactive gases, are
neither metal nor nonmetal, have very high
Ei and low (@ 0 kJ/mol) Eea.
• Table 6.8
• Only Kr and Xe react and they only react
with fluorine.
OCTET RULE
• Main group elements tend to undergo rxns
that leave them with 8 valence electrons
(octet, Noble gas configuration).
• Exceptions occur when there are low
energy d orbitals available for additional
electrons to fill. (Figure 6.10)