3.3.1 Chem. Properties of groups
Chem. Properties of groups
•Discuss the similarities and differences
in the chemical properties of elements
in the same group

How do the alkali metals react with oxygen?
All alkali metals react with oxygen in the
air to form metal oxides. This produces
a layer of dull oxide on the surface of the
metal, called tarnish.
The speed with which alkali metals react
with oxygen in the air increases going
down the group:
 lithium – tarnishes slowly
 sodium – tarnishes quickly
 potassium – tarnishes very quickly.
Why are alkali metals stored in oil?
The oil prevents them from reacting with
oxygen and tarnishing.

What is the equation for the reaction with oxygen?
The reaction between an alkali metal and oxygen is an
example of an oxidation reaction:
alkali metal + oxygen alkali metal oxide
The word and chemical equations for the reaction between
lithium and oxygen are:
lithium + oxygen lithium oxide
4Li (s) + O2 (g) 2Li2O (s)
What are the word and chemical equations for the reaction
that causes sodium to tarnish?
sodium + oxygen sodium oxide
4Na (s) + O2 (g) 2Na2O (s)

What does the reaction with water produce?
All the alkali metals react vigorously with water.
The reaction with water becomes more vigorous as you go
down the group.
It is an exothermic reaction as it releases a lot of heat.
The reaction produces a gas that ignites a lighted splint with
a squeaky pop. What is this gas?
When green universal indicator
is added to the reaction mixture,
it turns purple.
What does this tell you about
the products of this reaction?

What is the equation for the reaction with water?
This reaction creates alkaline hydroxide ions.
This is why the group 1 elements are called the alkali metals.
The general equation for the reaction between an alkali
metal reacting with water is:
alkali metal + water alkali metal + hydrogen
hydroxide
2M(s) + 2H2O(l) 2MOH (aq) + H2(g)

How does lithium react with water?
Lithium is the least reactive of
the alkali metals.
When added to water, it fizzes
and moves around slowly
across the surface of the water.
What is the equation for
this reaction?
lithium + water lithium + hydrogen
hydroxide
2Li (s) + 2H2O (l) 2LiOH (aq) + H2 (g)

How does sodium react with water?
When added to water, sodium fizzes more than lithium, and
moves quickly across the surface of the water.
The sodium melts as it
reacts, and it becomes
spherical and shiny, like
a ball bearing.
The hydrogen sometimes
catches fire because of
the heat from the reaction.
What is the equation for this reaction?
sodium + water sodium + hydrogen
hydroxide
2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g)

How does potassium react with water?
When added to water, the
potassium moves across the
surface of the water very quickly.
The reaction produces so much
heat that the hydrogen given off
catches alight.
What colour would the flame be?
Like sodium, it melts with the heat of the reaction.
What is the equation for this reaction?
potassium + water potassium + hydrogen
hydroxide
2K (s) + 2H2O (l) 2KOH (aq) + H2 (g)

How does electron structure affect reactivity?
The reactivity of alkali metals increases going down the
group. What is the reason for this?
 The atoms of each element get larger
Li going down the group.
increase in reactivity
 This means that the outer shell electron
gets further away from the nucleus and
Na is shielded by more electron shells.
 The further an electron is from the
positive nucleus, the easier it can be
lost in reactions.
K  This is why the reactivity of the alkali
metals increases going down group 1.

Flame tests
When group 2 metals are burned in oxygen, coloured
flames are produced. This is due to the presence of metal
ions. Flame tests exploit this fact.
The presence of certain metal ions can be identified by
noting the characteristic flame colour that results from
burning. The colours for group 2 metal ions are:
magnesium – bright white
calcium – brick red/orange
strontium – red/crimson
barium – pale green/yellow-green

Explaining flame tests
When heated, some electrons in an atom or ion are excited
to higher energy levels. When they fall back to their initial
levels, energy is emitted; sometimes seen as visible light.
Electrons may be excited by
different amounts into
different energy levels and
energy
drop back at different times. light
The colour of the flame is a heat
combination of all these
energy emissions.

Explaining the trend in reactivity
The reactivity of the elements
down group 2 from beryllium to
barium increases. Mg
This is because it is
successively easier to remove
electrons to form the 2+ ion. Ca
Although increased shielding
cancels the increased nuclear
Sr
charge down the group, the
increase in atomic radius results
in a decrease in the attractive
force between the outer Ba
electrons and the nucleus.