Group 13 / IIIA; Boron Group
An old name for this group was "earth metals" since they have some similarities to the alkali metals. The technical importance of aluminum is clear. It is, by the way, the most prominent metal in the earth's crust but not easy to make by "smelting".
Without boron (B) as doping element in silicon (Si) there would be no microelectronics but the major use of boron is in the glass industry. Boron is also used as alloying element in steel. Boron nitride (BN) is just as hard as diamond and thus finds uses.
Gallium (Ga) and Indium (In) are prominent in so-called III-V semiconductors indispensable for optoelectronics (e.g. Lases and LED's). Indium, in particular is also needed in quantities for making "ITO", short for indium-tin-oxide, the material of choice if you need a light-transparent conductor, e.g. for flat-panel displays or some kinds of solar cells.
Thallium (Tl) and its compounds are poisonous and thus not used much.
Table of Basic Data
 
Name
(German)		 Boron
Bor 		Aluminum
Aluminium 		Gallium
Gallium		 Indium
Indium		 Thallium
Thallium
Atomic number 5 13 31 49 81
Atomic mass [u] 10,81 26,98 69,72 114,82 204,38
Melting point [K] 2573 933,52 302,93 429,32 576,7
Melting point [oC] 2300 660,52  29,93 156,32 303,7
Melting point [oF]          
Boiling point [K] 2823 2740 2676 2353 1730
Density [g/cm3] 2,46 2,70 5,91 7,31 11,85
Ionization energy [eV] 8,30 5,97 6,0 5,79 6,11
Electronegativitiy 2,0 1,5 1,8 1,5 1,4
Atomic radius [pm] 83 143,1 122,1 162,6 170,4
Ionic radius [pm] 23 57 62 92 149
Oxidation numbers 3 3 3, 2, 1 3, 2, 1 3, 1
Lattice typ
Transformation temp. [oC]		 op
 fcc
 op
 tp
 fcc
232
hcp
Lattice constant [Å]
(a or c)		 8,93
5,06		 4,04 ?
?		 4,59
4,94		 3,45
5,52
Young's - Modul us [GPa] ? 70,5 (9,8) 10,5 8,0
Therm. expansion coefficient a
[10-6K-1] 		2,3 23,3 18 40 29
 
In case of doubt all numbers are for room temperatures
fcc = face centered cubic; lattice const. = a
bcc = body centered cubic
sc = simple cubic
hp = simple hexagonal
hcp = hexagonal close packed; lattice constants a and c.
op = simple orthorhombic, monoclinic, triclinic
tp = simple tetragonal
dia = diamond structure
r = trigonal or rhomboedral trigonal

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