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Group 1 the alkali metals
Contains the familiar reactive metals sodium and potassium as well as others
Francium at the bottom is radioactive. One of its isotopes is produced in radioactive decay of
uranium but is short-lived.
Using the rest of Group 1 you can predict its properties but can't realistically observe them.
Melting point (°C) Boiling point (°C) Density (g/cm3)
Li 181 1342 0.53
Na 98 883 0.97
K 63 760 0.86
Rb 39 686 1.53
Cs 29 669 1.88
Both the melting and boiling points are low for metals and decrease as you go down the
The densities tend to increase as you go down the group but not tidily. The first three are all
less dense than water and float.
The metals in this group are very soft, becoming softer as you go down the group.
They are shiny silver when cut but tarnish within seconds as they react with the oxygen.
Storage and handling
These metals are all reactive, getting more reactive as you go down the group. They all form
oxides quickly in air and react strongly with water to form alkali solutions of metal
To stop them reacting, lithium, sodium and potassium are stored in oil.
Rubidium and caesium are so reactive that they have to be stored in sealed glass tubes
Great care must be taken not to touch these metals as there could be enough sweat on you
skin to react with them.
Reactions with water
The main difference is how fast they happen.
Sodium floats because it is less dense than water. It melts because its melting point is low
and lots of heat is produced in the reaction. Because the hydrogen isn't given of
symmetrically around the ball the sodium is pushed around the surface of the water. A white
trail forms which is sodium hydroxide which dissolves to give an alkali solution.
This reaction is very similar to sodium but it's slower. Lithium's melting point is higher and
heat is produced slower so lithium doesn't melt.
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Potassium's reaction is faster than sodium's. Enough heat is produced to ignite the hydrogen
which burns with a lilac flame. The reaction often ends with the potassium spitting around. As
you go down the group, the metals become more reactive.…read more