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S and P-Block Elements >>
Alkali Metals
Alkali Metals
The group I comprising Li, Na, K, Rb, Cs & Fr are commonly called alkali metals. Francium is radioactive and has a very short life (half life of 21 minutes), therefore very little is known about it.
Electronic Configuration
The general electronic configuration of alkali metals may be represented by [noble gas] where n = 2 to 7
Table – I
[Some Physical properties of group 1 elements (alkali metals)]
|
Property
|
Elements
|
|
Li
|
Na
|
K
|
Rb
|
Cs
|
Fr
(Radioactive)
|
| Atomic Number |
3
|
11
|
19
|
37
|
55
|
87
|
| Electronic Configuration |
2s’
|
3s’
|
4s’
|
5s’
|
6s’
|
7s’
|
| Atomic Mass |
6.94
|
22.99
|
39.10
|
85.47
|
13.91
|
223
|
| Metallic radius (pm) |
152
|
186
|
227
|
248
|
265
|
375
|
| Ionic radius (M+/pm) |
76
|
102
|
138
|
152
|
167
|
180
|
|
Ionization enthalpy
(kJ mol–1)
|
I |
520
|
496
|
419
|
403
|
376
|
–
|
| II |
7298
|
3562
|
3051
|
2633
|
2230
|
–
|
|
Electro negativity
(Pauling Scale)
|
0.98
|
0.93
|
0.82
|
0.82
|
0.79
|
|
| Density/g cm–3 (at 298K) |
0.53
|
0.97
|
0.86
|
1.53
|
1.90
|
|
| Melting point/K |
454
|
371
|
336
|
312
|
302
|
|
| Boiling point/K |
1615
|
1156
|
1032
|
961
|
944
|
|
|
E°(V) at 298K for
M+(aq) + e–→ M(s)
|
–3.04
|
–2.714
|
–2.925
|
–2.930
|
–2.927
|
|
|
Occurrence in
Atmosphere
|
18*
|
227**
|
1.84**
|
78.12*
|
2.6*
|
|
*ppm (parts per million) ** percentage by weight
Alt text: physical properties of Alkali metals
Illustration:
Why Group 1 elements are called alkali metals?
Solution:
The Group 1 elements are called alkali metals because they form water soluble hydroxides.
Exercise:
Write three general characteristics of the elements of s-block of the periodic table which distinguish them from the elements of the other blocks.
Exercise:
Which alkali metal is most abundant in earth’s crust?