Group I and Group VII
elements
Where are the alkali metals?
The elements in group 1, on the left of the periodic table,
are called the alkali metals.
lithium
Li
sodium
Na
potassium
K
rubidium
Rb
caesium
Cs
francium
Fr
These metals are all very reactive and are rarely found in
nature in their elemental form.
Why are they called the ‘alkali
metals’?
The alkali metals are so
reactive that, as elements,
they have to be stored in
oil. This stops them reacting
with oxygen in the air.
Alkali metals are soft enough to be cut with a knife, and
the most common alkali metals, lithium, sodium and
potassium, all float on water.
The elements in group 1 also react with water and form
alkaline compounds. This is why they are called alkali
metals.
What are the properties of the alkali
metals?
The characteristic properties of the alkali metals are:
 They are soft and can be cut by a knife.
Softness increases going down the group.
 They have a low density.
Lithium, sodium and potassium float on water.
 They have low melting and boiling points.
These properties mean that the alkali metals are different to
typical metals. However, alkali metals do also share some
properties with typical metals:
 They are good conductors of
heat and electricity.
 They are shiny. This is only seen
when alkali metals are freshly cut.
What are the trends in density?
What is the trend in density?
The alkali metals generally become more dense going down
the group, but the trend is not perfect because potassium is
less dense than sodium.
Element
Density (g/dm3)
lithium
0.53
sodium
0.97
potassium
0.86
rubidium
1.53
caesium
1.87
Water has a density of 1 g/dm3.
Which elements in group 1 will float on water?
What are the trends in melting
point?
What are the trends in boiling
point?
What is the trend in melting and boiling
points?
The melting points and boiling points of alkali metals
decrease going down the group.
Element
Melting point (°C) Boiling point (°C)
lithium
181
1342
sodium
98
883
potassium
64
760
rubidium
caesium
39
28
686
671
The melting and boiling points decrease going down group 1
because the atoms get larger. Melting points are lower than for
typical, transition, metals, because alkali metals only have 1
electron in their outer shell. Not much heat energy is needed for
this electron to be lost.
Electron structure
All alkali metals have 1 electron in their outer shell. This
means that:
lithium
2,1
 They can easily obtain a full
outer shell by losing 1 electron.
sodium
2,8,1
 They all lose their outer shell
electron in reactions to form
positive ions with a +1 charge.
 They have similar physical and
potassium
chemical properties.
2,8,8,1
Electron structure and reactivity
increase in reactivity
The reactivity of alkali metals increases down the group.
What is the reason for this?
Li
Na
K
Rb
Cs
 The size of the element’s atoms, and the
number of full electron shells, increases down
the group.
 This means that, down the group, the electron in
the outer shell gets further away from the
nucleus and is shielded by more electron shells.
 The further away an electron is from the
positive attraction of the nucleus, the easier it
can be lost in reactions.
 This means that reactivity increases with the
size of the atom.
Group 7 – the halogens
The elements in group 7 of the periodic table, on the right,
are called the halogens.
F
fluorine
Cl
chlorine
Br
bromine
I
At
iodine
astatine
Why are they called the ‘halogens’?
Halogens are very reactive non metals.
They are all toxic or harmful
because they are so reactive.
Before antiseptics, iodine
was used to clean wounds as
it is harmful to all things,
including bacteria.
They are also never found free in nature because of their
reactivity – they are found as compounds with metals.
These halogen-metal compounds are salts, which give
halogens their name – ‘halo-gen’ means ‘salt-former’.
What are the general properties of the
halogens?
All the halogens are:
 non-metals and so do not conduct electricity
 brittle and crumbly when solid
 poisonous and smelly.
They become darker in colour down the group:
is pale yellow
is yellow-green
is red-brown
is grey
Halogens – what do they look like?
Chlorine
Bromine
Iodine
What is the physical state of the
halogens?
The melting and boiling points of the halogens increase
down the group, as the molecules become bigger.
Halogen
Relative
size
Melting
point (°C)
Boiling
point (°C)
State
-220
-118
gas
-101
-34
gas
-7
59
liquid
114
184
solid
What is the state of each halogen at room temperature?
Melting and boiling points of halogens
Halogen vapours
Bromine and iodine are not gaseous, but have low boiling
points. This means that they produce vapour at relatively
low temperature. They are volatile.
Bromine produces some
red-brown vapour, seen
here above the liquid
bromine in the jar.
When iodine is heated gently, it
changes directly from a solid to a
gas without first becoming a liquid.
This is called sublimation.
What is the electron structure of the
halogens?
All halogens have seven
electrons in their outer
shell. This means that:
 They can easily obtain a
full outer shell by gaining
one electron.
 They all gain an electron
in reactions to form
negative ions with a -1
charge.
 They have similar
chemical properties.
fluorine
2,7
chlorine
2,8,7
bromine
2,8,8,7
The reactivity of alkali metals decreases going down the
group. What is the reason for this?
 The atoms of each element get
F
larger going down the group.
 This means that the outer shell gets
further away from the nucleus and
is shielded by more electron shells.
Cl
 The further the outer shell is from
the positive attraction of the
nucleus, the harder it is to attract
another electron to complete the
outer shell.
 This is why the reactivity of the
halogens decreases going down
group 7.
Br
decrease in reactivity
How does electron structure affect reactivity?
How do halogen molecules exist?
All halogen atoms require one more electron to obtain a full
outer shell and become stable.
Each atom can achieve this by sharing one electron with
another atom to form a single covalent bond.
F
+
F

F
F
This means that all halogens exist as diatomic molecules:
F2, Cl2, Br2 and I2.
Reactions of the Group
I and Group VII
elements
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
4Li (s)
+
+
oxygen  lithium oxide
O2 (g)

2Li2O (s)
What are the word and chemical equations for the reaction
that causes sodium to tarnish?
sodium
4Na (s)
+ oxygen  sodium oxide
+ 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
2M(s)
 alkali metal + hydrogen
hydroxide
+ 2H2O(l) 
2MOH (aq) +
H2(g)
Lithium with water
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
hydroxide
+
hydrogen
2Li (s)
+
2H2O (l) 
2LiOH (aq)
+
H2 (g)
Sodium with water
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
2Na (s)
+
water

+ 2H2O (l) 
sodium
hydroxide
+
hydrogen
2NaOH (aq)
+
H2 (g)
Potassium with water
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
hydroxide
+
hydrogen
2K (s)
+
2H2O (l) 
+
H2 (g)
2KOH (aq)
How do alkali metals react with chlorine?
Alkali metals burst into flames when heated and added to
chlorine. They form metal chlorides.
alkali metal
+
chlorine  alkali metal chloride
The word and chemical equations for the reaction between
lithium and chlorine are:
lithium
+
2Li (s)
+
chlorine  lithium chloride
Cl2 (g)

2LiCl (s)
What are the word and chemical equations for the reaction
that produces sodium chloride?
sodium
+
2Na (s)
+
chlorine  sodium chloride
Cl2 (g)

2NaCl (s)