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CHEMISTRY 161

Chapter 8

Periodic Relationships Among the Elements

www.chem.hawaii.edu/Bil301/welcome.html

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REVISION

low IE

high EA

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EXCEPTIONS

1. d- and f-shell contraction

2. half and fully occupied shells

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5. Trends in Chemical Reactivity

diagonal relationships

charge density

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Hydrogen (1s1)

H + e- → H-

H → H+ + e- group 1 acids

group 7 hydrides

(LiH, CaH2)

LiH + H2O → LiOH + H2

0-1 +1

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Group 1 (ns1, n2)

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1. low ionization energies → very reactive

2. react with water and form hydrogen

2 M(s) + 2 H2O(l) → 2 MOH(aq) + H2(g)

3. react with oxygen and form oxides

2 M(s) + 1/2 O2(g) → M2O(s)

K, Rb, Cs, (Fr)M2O2 (peroxides)

MO2 (superoxides)

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Group 2 (ns2, n2)

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1. higher ionization energies → less reactive

2. react slowly with water and form hydrogen

M(s) + 2 H2O(l) → M(OH)2(aq) + H2(g)

3. react with oxygen and form oxides

M(s) + 1/2 O2(g) → MO(s)

MO2 (peroxides)

M = Mg, Ca, Sr, Ba, (Ra)

M = Ba, Sr, (Ra)

90Sr versus Ca

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Group 3 (ns2np1, n2)

semi metal(unreactive to water and oxygen)

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3. react with acids and form hydrogen

2 M(s) + 6 H+(aq) → 2 M3+(aq) + 3 H2(g)

1. react with oxygen and form oxides

4 M(s) + 3 O2(g) → 2 M2O3(s)

2. M (M = Ga, In, Tl) can be +3 and +1

stability of +1 increases from Ga via In to Tl

4. covalent versus ionic compounds(hydrides AlH3 and BeH2)

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Group 4 (ns2np2, n2)

semi metal

(no reaction with water)

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3. react with acids and form hydrogen

M(s) + 2 H+(aq) → M2+(aq) + H2(g)

1. react with oxygen and form oxides

E(s) + O2(g) → EO2(g/s)

2. E can be +4 and +2

stability of +2 increases from C to Pb

4. covalent versus ionic compounds

CO2/CO; SiO2/SiO; PbO2/PbO

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Group 5 (ns2np3, n2)

semi metal

oxidation numbers; oxides; oxoacids

N2

P4

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Group 6 (ns2np4, n2)

semi metal

oxidation numbers;oxoacids

O2

S8Se8

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Group 7 (ns2np5, n2)

oxidation numbers; oxoacids

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1. all elements exist as diatomic species X2

2. high electron affinities

X + e- → X-

isoelectronic with noble gases

3. react with hydrogen

X2 + H2 → 2 HX

acidity increases from HF to HI

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Group 8 (ns2np6, n2)

monoatomic species

Group 8 (ns2np6, n2)

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low reactivity

XePtF6, XeF4, XeO3, XeO4

KrF2

HArF

ionization energy decreases

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Oxides

ionic molecular

three dimensional discrete units

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Oxides

basic acidicamphoteric

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basic

Na2O(s) + H2O(l) → 2 NaOH(aq)

2 MgO(s) + 2 H2O(l) → 2 Mg(OH)2(aq)

MgO(s) + 2 HCl(l) → MgCl2(aq) + H2O(l)

acidic

CO2(g) + H2O(l) → H2CO3(aq)

P4O10(s) + 6 H2O(l) → 4 H3PO4(aq)

SO3(s) + H2O(l) → H2SO4(aq)

Cl2O7(s) + H2O(l) → 2 HClO4(aq)

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amphoteric

Al2O3(s) + 6 HCl(l) → 2 AlCl3(aq) + 3 H2O(l)

Al2O3(s) + 2 NaOH(aq) + 3 H2O → 2 Na[Al(OH)4](aq)

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SUMMARY

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Homework

Chapter 8

pages 310-322, problem sets