Group 1 Elements (Alkali Metals)
They include the following elements as arranged in the periodic table;
Name Symbol
Lithium Li
Sodium Na
Potassium K
Rubidium Rb
Caesium Cs
Francium Fr
Physical properties
They are grey or silver in colour and shiny when they are freshly cut
Their melting and boiling points become lower as go down the group
They become softer and easy to cut as you go down the group
They tarnish very quickly as you go down the group when exposed to air
They are stored under paraffin, oil or sealed glass tubes because they are very reactive. This prevents them from
being exposed to air and reacting with water or oxygen
Reasons why the metals are in group 1
1. They have one electron in the outermost energy level that gets lost when they become stable, i.e
Name Symbol Electron configuration
Lithium Li 2.1
Sodium Na 2.8.1
Potassiu K 2.8.8.1
m
2. They have similar chemical properties
Reactions with water
React with water to produce a metal hydroxide and hydrogen
Alkali metal + water alkali metal hydroxide + hydrogen gas
2M + 2H2O 2MOH + H2
Examples
Lithium
2Li (s) + 2H2O (l) 2LiOH (aq) + H2 (aq)
Sodium
2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (aq)
Potassium
2K (s) + 2H2O (l) 2KOH (aq) + H2 (aq)
The reactions of all alkali metals are similar but the difference is how quickly they happen. As you go down the group,
reactivity with water becomes more rapidly or even explosive.
Question
Predict the reaction of Rubidium and Caesium with water and what is formed.
Observations when Alkali metals react with water
Float on water because they are less dense than water
They melt into a ball because they have low melting points and a lot of heat is produced
A fizzing sound is produced indicating hydrogen gas is produced
They dart on water surface due to production of hydrogen gas that is not given off symmetrically hence propels the
metals around.
The metals dissolve in water forming a metal hydroxide solution that is colorless.
Metal hydroxide solution turns to a blue colour when a universal indicator is added confirming that it is alkaline
(base)
Reaction with air
Alkali metals tarnish when freshly cut to produce metal oxides.
4M(s) + O2 (g) 2M2O (s)
Example
4K(s) + O2 (g) 2K2O (s)
A freshly cut potassium reacts extremely rapidly, more quickly with oxygen in the air than sodium. Sodium is also more
reactive than lithium.
If the alkali metals are heated in the air the reactions become more vigorous and burn with different flame colours also
forming metal oxides:
Lithium burns with a red flame forming lithium oxide
Sodium burns with a yellow flame forming sodium oxide
Potassium burns with a lilac flame forming potassium oxide
Explaining the Increase in Reactivity
As you go down the group, reactivity increases (metals become more reactive)
Reason
*It depends on the distance between the outer electron and how strongly it is attracted to the nucleus that
contains the protons which are positively charged.
*As we move down the group, the number of shells increase and size of atoms increase, the outer electron is
further from nucleus hence is less strongly attracted by the nucleus and therefore more easily lost.
