Group 1 (alkali metals) elements - reactivity
Group 1 elements (alkali metals) were first discovered from 1807 onwards.
Some of the physical properties are shown below.
Element
Boiling point oC
Lithium
1342
Sodium
883
Potassium
760
Rubidium
686
Caesium
670
Melting point oC
181
98
63
39
29
Density g/cm3
Atomic mass
Diameter of atom
(nano-metres)
0.53
0.97
0.86
1.54
1.88
3.00
0.246
23
0.304
39.1
0.406
85.5
0.432
132.9
0.470
As the atomic mass (and the size of the atom) of the Group 1 alkali metals increases the:
 boiling point
 melting point
all decrease whilst the density increases.
The reason why these alkali metals are
reactive is that they all have one
electron in their outer shell.
This means that the atoms of the alkali
metals are not "very happy" and they
will do all they can to lose their one
lone outer electron
In order of reactivity caesium is the
most reactive followed by rubidium,
then potassium, sodium and lithium is
the least reactive.
Electronic configurations.
Element
Atomic
number
Electrons
in 2nd
shell
1
Electrons
in 3rd
shell
3
Electrons
in 1st
shell
2
Lithium
Electrons
in 4th
shell
Electrons
in 5th
shell
Sodium
11
2
8
1
Potassium
19
2
8
8
1
Rubidium
37
2
8
18
8
1
Caesium
55
2
8
18
18
8
Electrons
in 6th
shell
1
Electronic configurations (diagrams) for lithium, sodium and potassium are shown below.
NOTE
As the atom becomes bigger and bigger the
electron in the outer shell is held less tightly and
is more likely to escape.
So for caesium (size 0.470 nm)
 the outer electron is not held tightly.
 It can easily be lost.
Caesium IS very reactive.
So for lithium (size 0.246 nm)
 the outer electron is held tightly.
 It is hard to lose.
Lithium is NOT very reactive.
As these metals are so reactive they are stored:
 in an inert atmosphere (caesium and
rubidium)
 under oil (lithium, sodium and potassium)