Some Alkali Metals Subgroup Trends
Group I elements
- Silvery in colour, tarnish rapidly in air
- Are kept immersed in paraffin oil or in evacuated sealed ampoules
- Soft, have low boiling and melting points
- Low density
- Body-centred cubic structures are more spacy
| Li
| Na
| K
| Rb
| Cs
| Fr
| density, g/сm3
| 0.53
| 0.97
| 0.86
| 1.52
| 1.89
| 0.53
| Electronegativity
| 0.98
| 0.93
| 0.82
| 0.82
| 0.79
| -
| m. p., oС
|
| 97.8
| 63.5
| 38.7
| 28.5
|
| b. p., oС
|
| 883.1
|
|
| 678.6
|
| Rа, nm
| 0.152
| 0.154
| 0.227
| 0.248
| 0.265
| ~0.270
| Radius Е+, nm
| 0.068
| 0.098
| 0.133
| 0.149
| 0.165
| 0.175
| Ionisation energy
Е ® Е+, kJ∙mol-1
| 513.3
| 495.8
| 418.8
| 403.0
| 375.7
|
| Еo(Е+ + е = Е), V
| -3.05
| -2.71
| -2.92
| -2.93
| -2.92
| -
|
Melting points of Groups I and II elements is a function of its metallic bonds strength.The stronger the bond, the higher is the melting point
Metallic bond strength depends on:
(1)ionic radius,
(2)no. of valence electrons
Down the group, the size of cations increases
Þpolarizing power decreases
Þcompound with large anion become more stable
∴ thermal stability of carbonates & hydroxides of Group I metals increases down the group
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- THE TRENDS IN PAINTING IN THE 19TH CENTURY
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