Chemical Periodicity

1
CHAPTER 6

• Chemical Periodicity

2
Chapter Goals

• More About the Periodic Table
• Periodic Properties of the Elements
• Atomic Radii
• Ionization Energy
• Electron Affinity
• Ionic Radii
• Electronegativity

3
Chapter Goals

• Chemical Reactions and Periodicity
• Hydrogen the Hydrides
• Hydrogen
• Reactions of Hydrogen and the Hydrides
• Oxygen the Oxides
• Oxygen and Ozone
• Reactions of Oxygen and the Oxides
• Combustion Reactions
• Combustion of Fossil Fuels and Air Pollution

4
Chemical Reactions Periodicity

• In the next sections periodicity will be applied
  to the chemical reactions of hydrogen, oxygen,
  and their compounds.

5
Hydrogen and the Hydrides

• Hydrogen gas, H2, can be made in the laboratory
  by the reaction of a metal with a nonoxidizing
  acid.

Mg 2 HCl ???MgCl2 H2

• Hydrogen is commercially prepared by the
  thermal cracking of hydrocarbons.
• H2 is commonly used in the preparation of ammonia
  for fertilizer production.

C4H10 ? 2 C2H2 3 H2
6
Reactions of Hydrogen andthe Hydrides

• Hydrogen reacts with active metals to yield
  hydrides.

2 K H2 ? 2 KH

• In general for IA metals, this reaction can be
  represented as

2 M H2 ? 2 MH
7
Reactions of Hydrogen andthe Hydrides

• The heavier and more active group IIA metals have
  the same reaction with hydrogen.

Ba H2 ? BaH2

• In general this reaction for IIA metals can be
  represented as

M H2 ? MH2
8
Reactions of Hydrogen andthe Hydrides

• The ionic hydrides produced in the two previous
  reactions are basic.
• The H- reacts with water to produce H2 and OH-.

H- H2O ? H2 OH-

• For example, the reaction of LiH with water
  proceeds in this fashion.

9
Reactions of Hydrogen andthe Hydrides

• Hydrogen reacts with nonmetals to produce
  covalent binary compounds.
• One example is the haloacids produced by the
  reaction of hydrogen with the halogens.

H2 X2 ? 2 HX

• For example, the reactions of F2 and Br2 with
  H2 are

H2 F2 ? 2 HF H2 Br2 ? 2 HBr
10
Reactions of Hydrogen andthe Hydrides

• Hydrogen reacts with oxygen and other VIA
  elements to produce several common binary
  covalent compounds.
• Examples of this reaction include the production
  of H2O, H2S, H2Se, H2Te.

2 H2 O2 ? 2 H2O 8 H2 S8 ? 8 H2S
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Reactions of Hydrogen andthe Hydrides

• The hydrides of Group VIIA and VIA hydrides are
  acidic.

12
Reactions of Hydrogen andthe Hydrides

• There is an important periodic trend evident in
  the ionic or covalent character of hydrides.
• Metal hydrides are ionic compounds and form basic
  aqueous solutions.
• Nonmetal hydrides are covalent compounds and form
  acidic aqueous solutions.

13
Oxygen and the Oxides

• Joseph Priestley discovered oxygen in 1774 using
  this reaction

2 HgO(s) ??2 Hg(?) O2(g)

• A common laboratory preparation method for oxygen
  is

2 KClO3 (s) ?? 2 KCl(s) 3 O2(g)

• Commercially, oxygen is obtained from the
  fractional distillation of liquid air.

14
Oxygen and the Oxides

• Ozone (O3) is an allotropic form of oxygen which
  has two resonance structures.

• Ozone is an excellent UV light absorber in the
  earths atmosphere.

2 O3(g) ? 3 O2(g) in presence of UV
15
Reactions of Oxygen andthe Oxides

• Oxygen is an extremely reactive element.
• O2 reacts with most metals to produce normal
  oxides having an oxidation number of 2.

4 Li(s) O2(g) ? 2 Li2O(s)

• However, oxygen reacts with sodium to
  produce a peroxide having an oxidation number
  of 1.

2 Na(s) O2(g) ? Na2O2(s)
16
Reactions of Oxygen andthe Oxides

• Oxygen reacts with K, Rb, and Cs to produce
  superoxides having an oxidation number of -1/2.

2 Na(s) O2(g) ? Na2O2(s)

• Oxygen reacts with IIA metals to give normal
  oxides.

2 M(s) O2(g) ? 2 MO(s) 2 Sr(s) O2(g) ? 2
SrO(s)
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Reactions of Oxygen andthe Oxides

• At high oxygen pressures the IIA metals can form
  peroxides.

Ca(s) O2(g) ? CaO2(s)

• Metals that have variable oxidation states, such
  as the d-transition metals, can form variable
  oxides.
• For example, in limited oxygen

2 Mn(s) O2(g) ? 2 MnO(s)

• In excess oxygen

4 Mn(s) 3 O2(g) ? 2 Mn2O3(s)
18
Reactions of Oxygen andthe Oxides

• Oxygen reacts with nonmetals to form covalent
  nonmetal oxides.
• For example, the carbon reactions with oxygen
• In limited oxygen

2 C(s) O2(g) ? 2 CO(g)

• In excess oxygen

C(s) O2(g) ? CO2(g)
19
Reactions of Oxygen andthe Oxides

• Phosphorous reacts similarly to carbon forming
  two different oxides depending on the oxygen
  amounts
• In limited oxygen

P4(s) 3 O2(g) ? P4O6(s)

• In excess oxygen

P4(s) 5 O2(g) ? P4O10(s)
20
Reactions of Oxygen andthe Oxides

• Similarly to the nonmetal hydrides, nonmetal
  oxides are acidic.
• Sometimes nonmetal oxides are called acidic
  anhydrides.
• They react with water to produce ternary acids.
• For example

CO2(g) H2O (?) ? H2CO3(aq)
Cl2O7(s) H2O (?) ? 2 HClO4(aq)
As2O5(s) 6 H2O(?) ? 4 H3AsO4(aq)
21
Reactions of Oxygen andthe Oxides

• Similarly to the hydrides, metal oxides are
  basic.
• These are called basic anhydrides.
• They react with water to produce ionic metal
  hydroxides (bases)

Li2O(s) H2O(?) ? 2 LiOH(aq)
CaO(s) H2O (?) ? Ca(OH)2(aq)

• Metal oxides are usually ionic and basic.
• Nonmetal oxides are usually covalent and
  acidic.
• An important periodic trend.

22
Reactions of Oxygen andthe Oxides

• Nonmetal oxides react with metal oxides to
  produce salts.

Li2O(s) SO2(g) ? Li2SO3(s)
Cl2O7(s) MgO(s) ? Mg(ClO4)2(s)
23
Combustion Reactions

• Combustion reactions are exothermic redox
  reactions
• Some of them are extremely exothermic.
• One example of extremely exothermic reactions is
  the combustion of hydrocarbons.
• Examples are butane and pentane combustion.

2 C4H10(g) 13 O2(g) ? 8 CO2(g) 10 H2O(g)
C5H12(g) 8 O2(g) ? 5 CO2(g) 6 H2O(g)
24
Fossil Fuel Contaminants

• When fossil fuels are burned, they frequently
  have contaminants in them.
• Sulfur contaminants in coal are a major source of
  air pollution.
• Sulfur combusts in air.

S8(g) 8 O2(g) ? 8 SO2(g)

• Next, a slow air oxidation of sulfur dioxide
  occurs.

2 SO2(g) O2(g) ? 2 SO3(g)

• Sulfur trioxide is a nonmetal oxide, i.e. an
  acid anhydride.

SO3(g) H2O(?) ? H2SO4(aq)
25
Fossil Fuel Contaminants

• Nitrogen from air can also be a source of
  significant air pollution.
• This combustion reaction occurs in a cars
  cylinders during combustion of gasoline.

N2(g) O2(g) ? 2 NO(g)

• After the engine exhaust is released, a slow
  oxidation of NO in air occurs.

2 NO(g) O2(g) ? 2 NO2(g)
26
Fossil Fuel Contaminants

• NO2 is the haze that we call smog.
• Causes a brown haze in air.
• NO2 is also an acid anhydride.
• It reacts with water to form acid rain and,
  unfortunately, the NO is recycled to form more
  acid rain.

3 NO2(g) H2O(?) ? 2 HNO3(aq) NO(g)
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End of Chapter 6