© Boardworks Ltd 2003 THE ALKALI METALS. © Boardworks Ltd 2003 Alkali metals and the Periodic Table These are the alkali metals or Group 1 Elements. H

© Boardworks Ltd 2003

THE ALKALI METALS


Alkali metals and the Periodic Table

These are the alkali metals or Group 1 Elements.

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

Li

Na

K

Rb

Cs

Fr


Electronic Structure

• All the Group 1 elements have 1 electron in the outermost shell.

Li

Na

K

Rb

Cs

Lithium

Sodium

Potassium

Rubidium

Caesium

2,8,1

2,8,8,1

2,1


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 Symbol Density

Lithium Li 0.53

Sodium Na 0.97

Potassium K 0.86

Rubidium Rb 1.53

Caesium Cs 1.88


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 Melt. Point (C)

Lithium 181

Sodium 98

Potassium

Rubidium 39

Caesium

Can you predict the missing data?

63

29


Trends in Chemical Reactivity

Reactivity increases down the group.

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.

Li

Na

K

Rb

Cs

Rea

ctiv

ity I

ncre

ases


Reactivity and Electron Structures

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.

Both factors make it easier to lose the outer electron as you go down the group.

Rea

ctiv

ity

Incr

ease

s


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

H HO

H HO

HH

Li+

+Li

HO-

HO-

LiLi


Reaction of Lithium with Water

Lithium fizzes quickly in water forming lithium hydroxide and hydrogen.

Lithium + water Lithium hydroxide + hydrogen

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

The solution that remains is strongly alkaline.


Reaction of Sodium with Water

Sodium fizzes very quickly in water. The gas given off can be ignited by a lighted splint.

Sodium + water Sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

sodium on water enlarged


Potassium with Water

• Lithium fizzes. Sodium reacts more vigorously. • What will potassium do?

Potassium + water

2K(s) + 2H2O(l)

Potassium hydroxide + hydrogen

2KOH(aq) + H2(g)

What will the word equation and chemical equations be for the reaction of potassium with water?

Potassium + water


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

Na(s) + O2 (g)

sodium oxide

2Na2O (s)4


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

Na(s) + Cl2 (g)

Sodium chloride

2NaCl (s)2


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


Using sodium to transfer heat

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.

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.


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.


Nuclear Industry Representatives groupNuclear 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.


Anti-Nuclear Protest groupAnti-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.


Dr Ivan Idea SyndicateDr 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?


Dr Ivan Idea Syndicate 2Dr Ivan Idea Syndicate 2Some data on the metals that melt below 500oC.

Metal Symbol At Mass Melt Point (oC ) Relative costMercury Hg 200.59 -38.7 10Caesium Cs 132.9 28.6 25Gallium Ga 69.72 29.9 1055Francium Fr 223 30 unavailableRubidium Rb 85.47 39 198Potassium K 39.1 63.8 7.4Sodium Na 22.99 98 1Indium In 114.82 156.8 unavailableLithium Li 6.94 179 26


How many electrons do the alkalimetals have in their outer shell?

A. 1B. 2C. 4D. 7


What charge ions are formed by thealkali metals?

A. 4B. 3C. 2D. 1


Which answer places the alkali metals in order of increasing reactivity?

A. Na, Li, K,B. K, Na, LiC. Li, Na, KD. Li, K, Na


When alkali metals react with waterwe get:

A. Hydrogen + a metal oxideB. Oxygen + a metal oxide C. Hydrogen + a metal hydroxideD. Oxygen +a metal hydroxide


What will the melting point of caesium be?

A. -10oC B. 0oC C. 25oC D. 38oC

181

98

63

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0

50

100

150

200

0 2 4 6 8

Period

M.P

t (C

)

Li

Na

KRb Cs Fr

Documents

© Boardworks Ltd 2003 THE ALKALI METALS. © Boardworks Ltd 2003 Alkali metals and the Periodic Table These are the alkali metals or Group 1 Elements. H