Alkali Metals

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THE ALKALI METALS
© Boardworks Ltd 2005
Alkali metals and the Periodic Table
These are the alkali metals or Group 1 Elements.
H
Li Be
B C N O
Na Mg
Al Si P S
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po
Fr Ra Ac Rf Db Sg Bh Hs Mt ? ? ?
F
Cl
Br
I
At
He
Ne
Ar
Kr
Xe
Rn
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Electronic Structure
• All the Group 1 elements have 1 electron in the
outermost shell.
2,1
Li
Lithium
Na
Sodium
K
Potassium
Rb
Rubidium
Cs
Caesium
2,8,1
2,8,8,1
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Trends in Density
Lithium, sodium and potassium are all less dense than
water and so will float.
Densities follow a general, although not perfect, trend.
Element
Lithium
Sodium
Potassium
Rubidium
Caesium
Symbol
Li
Na
K
Rb
Cs
Density
0.53
0.97
0.86
1.53
1.88
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Melting Points
The atoms in the Group 1
elements are bonded together
using just one outer shell
electron per atom.
As a result, melting points are
low compared to most metals.
Element
Lithium
Sodium
Potassium
Rubidium
Caesium
Melt. Point
(C)
181
98
63
39
28
Can you predict the missing data?
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Reactivity increases down the group.
Li
Reactions all involve the loss of the
outermost electron which changes the
metal atom into a metal 1+ ion.
Losing this electron seems to get
easier as we go down the group.
Na
K
Rb
Reactivity Increases
Trends in Chemical Reactivity
Cs
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1. The outer electron (-) gets further
from the nucleus (+) as you go
down the group. This reduces the
force of attraction.
2. The inner shells ‘shield’ the
outermost electron from the
attraction from the nucleus.
Reactivity Increases
Reactivity and Electron Structures
Both factors make it easier to lose
the outer electron as you go down
the group.
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Reaction with Water
The Group 1 elements all react
vigorously with water.
Hydrogen gas is produced which
sometimes catches fire.
An alkali is left behind in the
solution which is why these
elements are often called ‘The
Alkali Metals’.
Reaction of Lithium
Li
H
Li
H
O H
Li
O
O
H
H
Li
+
+
O H
H
H
-
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Reaction of Lithium with Water
Lithium fizzes quickly in water forming lithium hydroxide
and hydrogen.
Lithium + water g Lithium hydroxide + hydrogen
2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g)
The solution that remains is
strongly alkaline.
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Reaction of Sodium with Water
Sodium fizzes very quickly in water. The gas given off can
be ignited by a lighted splint.
Sodium + water g Sodium hydroxide + hydrogen
2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)
sodium on water
enlarged
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Potassium with Water
• Lithium fizzes. Sodium reacts more vigorously.
• What will potassium do?
What will the word equation
and chemical equations be
for the reaction of potassium
with water?
Potassium + water
Potassium + water 
Potassium hydroxide + hydrogen
2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
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The Group 1 Metals and oxygen
The Group 1 elements burn in air to form metal oxides.
Don’t try to put them out with water!
Lithium + oxygen

Lithium Oxide
4Li (s) + O2(g)  2 Li2O (s)
What will the word equation and chemical equations be
for the reaction of sodium with air?
Sodium + oxygen 
4 Na(s) +
O2 (g) 
sodium oxide
2Na2O (s)
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The Group 1 Metals and chlorine
The Group 1 elements burn in chlorine to form metal
chlorides.
Lithium + chlorine

Lithium chloride
2Li (s) + Cl2(g)  2 LiCl (s)
What will the word equation and chemical equations be
for the reaction of sodium with chlorine?
Sodium + chlorine 
2 Na(s) +
Sodium chloride
Cl2 (g)  2NaCl (s)
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Uses of the Group 1 Metals
The metals themselves are too reactive to have
many uses although sodium vapour gives street
lights their yellow glow.
Lithium metal is used to improve the strength of
aircraft alloys and is also used in some
electrical batteries.
Common sodium compounds include “salt”,
(sodium chloride), “bicarbonate” (sodium
hydrogen carbonate), washing soda (sodium
carbonate) and caustic soda (sodium
hydroxide.)
Potassium compounds are used in “NPK
fertilisers”, in weedkillers, explosives and many
other chemicals.
sodium light
potassium
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Using sodium to transfer heat
The activity
Following an accident at a nuclear power station three groups
are represented at a public meeting.
The debate centres around an accident involving a spill of
molten sodium metal which was being used to cool the reactor.
It needs to include:
The benefits of using sodium to transfer
heat and the fact that risks resulting from
chemical reactivity are containable.
The chemical reactivity of sodium and
the fact that if containment did fail the
whole power station could blow up.
Whether there are other safer metals
that could be used in place of sodium.
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The Incident
• Most power stations burn a fossil fuel and use water to
transfer heat from the burners to the turbine area.
• An alternative to water is sodium. Although solid it melts
fairly easily and is a better conductor of heat than water.
• This has prompted its use as a coolant to absorb and
transfer the heat produced in nuclear power stations.
• To Japan, a country with no fossil fuels, nuclear power is
particularly attractive. However, in 1996 Japan’s nuclear
industry suffered a setback when a split in a stainless
steel pipe spewed 3 tonnes of molten sodium over the
reactor floor.
• Nuclear representatives say there was no radiation leak
and opponents to nuclear power were whipping up public
concern.
• Anti-nuclear protestors say that had it leaked underneath
the floor the entire nuclear station would have been at
risk.
• The government agreed to make plans about how to deal
with a nuclear accident just in case one did ever happen.
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Nuclear Industry Representatives group
• Make a case as to why Japan must have nuclear
power.
• Spell out the very low accident rate in the industry.
• Explain why a liquid that can absorb heat better is a
good thing (safer?) for a nuclear reactor.
• Spell out the fact that you understand the common
reactions of sodium and had already set in place
systems to prevent these reactions being a danger.
• Make clear that there is no totally safe way of
generating energy and that use of fossil fuels also
entails accidents and guaranteed pollution.
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Anti-Nuclear Protest group
• Explain that risk assessment must take account both of
the chances of an accident and the impact of that
accident. Leaked long lasting radioactive material or
even melt-down and nuclear explosion!
• Challenge the use of sodium (rather than larger
volumes of water) as representing a needless risk.
• Spell out in detail the possibility of explosive reactions
involving sodium and potentially devastating outcomes.
• Other fuels are available even if they have to be
imported.
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Dr Ivan Idea Syndicate
• One of the main reasons for using sodium is that it
melts easily and, as a metal, it conducts heat well.
• Check out the melting point, reactivity and toxicity of
other metals and consider the feasibility of using
them.
• Are there particular risks you would need to guard
against? Can you suggest ways to minimise these?
• Or - should you just go back to using water for heat
transfer?
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Dr Ivan Idea Syndicate 2
Some data on the metals that melt below 500oC.
Symbol At Mass Melt Point (oC ) Relative cost
Metal
10
-38.7
200.59
Hg
Mercury
25
28.4
132.9
Cs
Caesium
1055
29.9
69.72
Ga
Gallium
unavailable
30
223
Fr
Francium
198
39
85.47
Rb
Rubidium
7.4
63.8
39.1
K
Potassium
1
98
22.99
Na
Sodium
unavailable
156.8
114.82
In
Indium
26
179
6.94
Li
Lithium
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How many electrons do the alkali
metals have in their outer shell?
A.
B.
C.
D.
1
2
4
7
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What charge ions are formed by the
alkali metals?
A.
B.
C.
D.
4
3
2
1
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Which answer lists the alkali metals in
order of increasing reactivity?
A. Na, Li, K,
B. K, Na, Li
C. Li, Na, K
D. Li, K, Na
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When alkali metals react with water
we get:
A.
B.
C.
D.
Hydrogen + a metal oxide
Oxygen + a metal oxide
Hydrogen + a metal hydroxide
Oxygen +a metal hydroxide
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What will the melting point of caesium be?
A. -10oC
B. 0oC
C. 28oC
D. 38oC
200
181
Li
M.Pt (C)
150
100
98
Na
50
63
K
39
R
0
0
2
4
28
Cs
Fr
6
8
Period
© Boardworks Ltd 2005
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