Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 110

General Chemistry

Summer 2006

Lecture Notes::Lec 19_26 June

© R. Paselk 2006
 
     
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The Representative Elements, cont.

Group 2 Chemistry, cont.

Group III

Chemistry

What is a metal and what are metallic properties?

  • Generally good conductors of heat and electricity, most are malleable (can be pounded to thin sheets) and ductile (can be drawn into wires), and they have high reflectivity and luster.
  • Metals tend to form positive ions, and their hydroxides are basic.

Group III, Boron, Aluminum, Galium, Indium, and Thallium, introduces a couple of characteristics that will continue in varying degrees with the other p-block elements.

  1. The higher oxidation state decreases in stability as we go down the group. Thus for Group III we see the +3 oxidation state is important for all Group III elements, and the only oxidation state seen for example for Al, +1 is also an important oxidation state for Tl.
  2. The metallic character of the elements for identical oxidation states increases as we go down the group.
    B(OH)3(aq) + H2O(l) B(OH)4-(aq) + H+(aq)
    2Al(s) + 6H+(aq) 2Al3+(aq) + 3H2(g)
    2Al(s) + 6H2O(l) + 2OH-(aq) 2Al(OH)4-(aq) + 3H2(g)

Properties of Group III

Property B Al Ga In Tl
Outer electron configuration 2s22p1 3s23p1 4s23d104p1 5s24d105p1 6s24f145d106p1
Melting point (°C) 2300 660 29.7 156 304
Density (g/cm3) 2.37 2.70 5.90 7.3 11.9

Ionization energies - 1st & sum of 1-3 (kJ/mol)

M(s) M3+(aq) + 3 e-

800.6

6886

577.6

5137

578.8

5520

558

5063

589.3

5415

Standard Reduction Potentials (V, 25°C)

M2+(aq) + 2 e- M(s)

-0.87 -1.66 -0.53 -0.34 -0.72
Electronegativity 2.0 1.6 1.8 1.8 1.6

Group IV

Chemistry

Group IV shows a very obvious transition from a non-metal to increasingly metallic elements going down the group, ending in true metals.

Group IV give perhaps the most obvious example of the difference in properties between elements of Period 2 and higher Periods, since carbon, as a very distinct non-metal, behaves much differently than any of the other Group IV members.

The elements from silicon to lead show a nice transition of properties towards increasingly metallic.

The group shows an obvious "inert pair effect" with silicon and germanium exhibiting the +4 oxidation state, while Tin and lead exhibit both +2 and +4 oxidation states.

Properties of Group IV

Property C Si Ge Sn Pb
Outer electron configuration 2s2p2 3s2p2 4s23d104p2 5s24d105p2 6s24f145d106p2
Melting point (°C) 3550 (dia) 1410 938 505 601
Density (g/cm3) 2.25 (graph) 2.33 5.35 7.28 11.3

Ionization energies - 1st & sum of 1-4 (kJ/mol)

M(s) M4+(aq) + 4 e-

1086

14,280

787

9,947

762

10,000

709

8,988

715

9,325

Standard Reduction Potentials (V, 25°C)

M2+(aq) + 2 e- M(s)

- - - -0.138 -0.126
Electronegativity 2.5 1.8 1.8 1.8 1.8


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Last modified 26 June 2006