Transcript Chapter 20

Chapter 20
The Representative
Elements
Section 20.1
A Survey of the Representative Elements
The Atomic Radii of
Some
Representative
Elements (in
Picometers)
Return to TOC
Copyright © Cengage Learning. All rights reserved
2
Section 20.2
Atomic
The
Group
Masses
1A Elements
Reaction of Group 1A Metals
• Reactions with water:
2Li(s) + 2H2O → 2LiOH + H2
2Na(s) + 2H2O → 2NaOH + H2
2K(s) + 2H2O → 2KOH + H2
2Rb(s) + 2H2O → 2RbOH + H2
2Cs(s) 2H2O → 2CsOH + H2
(aq)
(aq)
(aq)
(aq)
(aq)
2X(s) 2H2O → 2XOH + H2
(aq)
Return to TOC
Copyright © Cengage Learning. All rights reserved
3
Section 20.2
Atomic
The
Group
Masses
1A Elements
Reaction of Group 1A Metals
• In the presence of excess oxygen:
4Li + O2 → 2Li2O
2Na + O2 → Na2O2
K + O2 → KO2
Rb + O2 → RbO2
Cs + O2 → CsO2
• In the presence of a halogen:
2Na + Cl2 → 2NaCl
Return to TOC
Copyright © Cengage Learning. All rights reserved
4
Section 20.2
Atomic
The
Group
Masses
1A Elements
Reactions of Group 1A Oxides
In water…
• oxides form hydroxides
Li2O + H2O → 2LiOH
•
peroxides form hydroxides and hydrogen peroxide
Na2O2 + 2H2O → 2NaOH + H2O2
• superoxides form hydroxides and hydrogen peroxide and
oxygen
2KO2 + 2H2O → 2KOH + 2H2O2 + O2
Return to TOC
Copyright © Cengage Learning. All rights reserved
5
Section 20.2
Atomic
The
Group
Masses
1A Elements
Reactions of Group 1A Oxides continued…
• In dilute acid, instead of a base forming, an acid-base
reaction occurs and forms a salt and the other products
from reaction with water.
Li2O + HCl → LiCl + H2O
Na2O2 + HCl → NaCl + H2O2
KO2 + HCl → KCl + H2O2 + O2
Return to TOC
Copyright © Cengage Learning. All rights reserved
6
Section 20.3
The Chemistry
Mole
of Hydrogen
Hydrides
• Binary compounds containing hydrogen:
 Ionic hydrides:
hydrogen + the most active metals (group I and group II)
(eg; LiH, CaH2)
 Covalent hydrides:
hydrogen + other nonmetals
(eg; H2O, CH4, NH3)
 Metallic (interstitial) hydrides:
transition metal crystals treated with H2 gas
Return to TOC
Copyright © Cengage Learning. All rights reserved
7
Section 20.3
The Chemistry
Mole
of Hydrogen
Exercise
Predict the products formed by the following
reactants:
LiH(s) + H2O(l) → H2(g) + LiOH(aq)
Ionic hydrides react with water to produce hydrogen gas and a
hydroxide.
Return to TOC
Copyright © Cengage Learning. All rights reserved
8
Section 20.3
The Chemistry
Mole
of Hydrogen
Reaction of Group 2A Metals
• Reactions with water:
Be has no rxn with water
Mg(s) + H2O(l) → Mg(OH)2 + H2
Ca(s) + 2H2O(l) → Ca(OH)2 + H2
Sr(s) + 2H2O(l) → Sr(OH)2 + H2
(s)
(aq)
(aq)
More reactive with water as you go down the group
X(s) + 2H2O → X(OH)2 + H2
(aq)
Return to TOC
Copyright © Cengage Learning. All rights reserved
9
Section 20.4
The Group 2A Elements
Reactions of Group 2A Metals
Return to TOC
Copyright © Cengage Learning. All rights reserved
10
Section 20.5
The Group 3A Elements
• Group 3A elements generally show the increase
in metallic character in going down the group
that is characteristic of the representative
elements.
• B, Al, Ga, In, Tl
• Notice that Boron is a nonmetal!
Return to TOC
Copyright © Cengage Learning. All rights reserved
11
Section 20.5
The Group 3A Elements
Some Important Reactions
Return to TOC
Copyright © Cengage Learning. All rights reserved
12
Section 20.5
The Group 3A Elements
Complex ion formation of Al
•
Al(H2O)63+ ↔ Al(OH)(H2O)52+ + H+
• Salt that produces an acidic solution
• Lewis acid base reaction
What species is acting as the Lewis acid? Lewis base?
Al
OH-
Return to TOC
Copyright © Cengage Learning. All rights reserved
13
Section 20.6
The Group 4A Elements
• Contains two of the most important elements on
earth: carbon and silicon.
• Can form four covalent bonds to nonmetals.
 CH4, SiF4, GeBr4
Return to TOC
Copyright © Cengage Learning. All rights reserved
14
Section 20.8
The Chemistry of Nitrogen
• Exhibits varied chemical properties.
• N, P, As, Sb, Bi
• Compounds of N
– NH3 NF3 only 3 bonds total
• Compounds of P
– PH3, PF3, but also PF6
How???
Return to TOC
Copyright © Cengage Learning. All rights reserved
15
Section 20.8
The Chemistry of Nitrogen
Nitrogen Fixation
• The process of transforming N2 to other
nitrogen–containing compounds.
• The Haber Process:
N2(g) + 3H2(g) → 2NH3(g)
∆Ho = -92 kJ
Return to TOC
Copyright © Cengage Learning. All rights reserved
16
Section 20.8
The Chemistry of Nitrogen
Nitrogen Oxides
• Nitrogen in its oxides has oxidation states from
+1 to +5.

In other compounds, nitrogen could have oxidation
states of -1 to -3.
Compound
N 2O
NO
N 2O 3
NO 2
HNO 3
Copyright © Cengage Learning. All rights reserved
Oxidation State of N
+1
+2
+3
+4
+5
Return to TOC
17
Section 20.8
The Chemistry of Nitrogen
Nitrogen Oxyacids
• Nitric acid, HNO3 (strong acid)
hv
4HNO3 (l ) 
 4NO2 (g ) + 2H2O(l ) + O2 (g )
• Nitrous acid, HNO2 (weak acid)
HNO2 (aq )
+

2
H (aq ) + NO (aq )
Return to TOC
Copyright © Cengage Learning. All rights reserved
18
Section 20.8
The Chemistry of Nitrogen
The Ostwald Process
Return to TOC
Copyright © Cengage Learning. All rights reserved
19
Section 20.9
The Chemistry of Phosphorus
Phosphorus Oxyacids
• P4O10 + H2O → H3PO4 (phosphoric acid)
• P4O6 + H2O → H3PO3 (phosphorous acid)
• Hypophosphorous acid, H3PO2
Return to TOC
Copyright © Cengage Learning. All rights reserved
20
Section 20.12
The Chemistry of Sulfur
Sulfur Oxide Reactions
2SO2(g) + O2(g) → 2SO3(g)
SO2(g) + H2O(l) → H2SO3(aq) (sulfurous acid)
SO3(g) + H2O(l) → H2SO4(aq) (sulfuric acid)
Return to TOC
Copyright © Cengage Learning. All rights reserved
21
Section 20.13
The Group 7A Elements
Preparation of Hydrogen Halides
H2(g) + X2(g)
2HX(g)
• When dissolved in water, the hydrogen halides
behave as acids, and all except hydrogen fluoride
are completely dissociated (strong acids)
Return to TOC
Copyright © Cengage Learning. All rights reserved
22
Section 20.13
The Group 7A Elements
Halogen Oxyacids and Oxyanions
•
•
All halogens except fluorine combine with various
numbers of oxygen atoms to form a series of oxyacids
Notice the varying oxidation states of the halogen.
Return to TOC
Copyright © Cengage Learning. All rights reserved
23
Section 20.13
The Group 7A Elements
Halogen Oxyacids and Oxyanions
• The strengths of these acids vary in
direct proportion to the number of
oxygen atoms attached to the halogen,
with the acid strength increasing as
more oxygens are added.
Return to TOC
Copyright © Cengage Learning. All rights reserved
24
Section 20.14
The Group 8A Elements
Noble Gases
• He and Ne form no compounds.
• Kr and Xe have been observed to form
chemical compounds:
Xe(g) + 2F2(g) → XeF4(s) [6 atm, 400oC]
XeF6(s) + 3H2O(l) → XeO3(aq) + 6HF(aq)
Return to TOC
Copyright © Cengage Learning. All rights reserved
25
Section 20.14
The Group 8A Elements
Of course there are more reaction types to consider
• Refer to Packet from Winter Break for more reaction
types
• (Ch 9, 10, 13 Chemical Equations Handouts)
Return to TOC
Copyright © Cengage Learning. All rights reserved
26