Group 1 / IA; Alkali Group

The akali group formally contains hydrogen (H) even so this element is not counted among the alkali metals and thus not listed below.
Potassium (K) and sodium (Na) are ubiquitous, while rubidium (Rb), lithium (Li) and cesium (Cs) are rarer. Francium (Fr) is radioactive and not found in nature.Alltogether the alkali metals provide for about 5 % of the elements in the crust of the earth. They are very reactive and thus are never found in the elementals state
Alkali metals are very soft and have typically low melting points. They are rarely uised in the elemental stage (liquid sodium is a coolant in some nuclear reactors) but are absolutely indispensable in compounds. Just consider rock salt (NaCl) or the potassium nitride (KNO3) in fertilizers. The lithium ion battery has a bright future, needing millions of tons of lithium for its production.
 
Table of Basic Data
 
Name
(German)		 Lithium
Lithium		 Sodium
Natrium		 Potassium
Kalium 		Rubidium
Rubidium		 Cesium
Cäsium		 Francium
Francium
Atomic number 3 11 19 37 55 87
Atomic mass [u] 6,94 22,99 39,10 85,47 132,91 223,02
Melting point [K] 453,69 370,95 336,8 312,2 301,55 300
Melting point [oC] 180,69 97,95 63,8 39,2 28,55 27
Melting point [oF] 357 208 147 102 83.4 81
Boiling point [K] 1590 1165 1047 961 963 950
Density [g/cm3] 0,53 0,97 0,86 1,53 1,90 ?
Ionization energy [eV] 5,39 5,14 4,34 4,18 3,89 4,0
Electro-negativitiy 1,0 1,0 0,9 0,9 0,9 0,9
Atomic radius [pm] 155 153,7 227 247,5 265,5 270
Oxidation numbers 1 1 1 1 1 1
Ionic radius [pm] 78 98 133 149 165 180
lattice typ
Transformation temp. [oC]
bcc
?
fcc
-195
hcp
bcc
-237
fcc
bcc
bcc
bcc
?
Lattice constant [Å]
(a or c)		 3,51 4,28
?		 5,33 5,62 2,67 ?
Young's - Modul us [GPa] 11,5 8,93 3,53 2,35 1,47 ?
Therm. expansion coefficient a
[10-6K-1]		 46,6 72 83 90 ? ?
 
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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