IONIC BONDS MAIN GROUP CHEMISTRY

Periodicity of Properties

Main Group Chemistry

IONIC BONDSIONIC 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)

• Start with elemental K and F2 (p 215)• K(s) K(g) Sublimation energy > 0• K(g) K+(g) + e- Ei > 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 E i, 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)