metals chapter 5. metals look at the periodic table look at the periodic table how many elements are...
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MetalsMetals
Chapter 5Chapter 5
MetalsMetals
Look at the periodic tableLook at the periodic table How many elements are metals?How many elements are metals?
Look around this roomLook around this room How many things are made out of metals or How many things are made out of metals or
metal alloys?metal alloys?
Why do we use metals so much?Why do we use metals so much?
Can you think of any properties of metals?Can you think of any properties of metals?
Uses of MetalsUses of Metals
Why do we use metals?Why do we use metals? The strength of metals is useful when building The strength of metals is useful when building
robust structures.robust structures. The lightness and strength of some metals are The lightness and strength of some metals are
useful for boats and aircraftuseful for boats and aircraft The ability to form wire from metals is applied The ability to form wire from metals is applied
in many different objects from copper wiring to in many different objects from copper wiring to jewelleryjewellery
Electricity is transmitted by metals in both the Electricity is transmitted by metals in both the home or industryhome or industry
Metals can be used to make diverse objects Metals can be used to make diverse objects which can be moulded and shapedwhich can be moulded and shaped
Useful Properties of MetalsUseful Properties of Metals Elements we classify as metals have all or Elements we classify as metals have all or
most of the following properties. They:most of the following properties. They: Are good conductors of electricityAre good conductors of electricity Are good conductors of heatAre good conductors of heat Are malleable Are malleable
Can be shaped by beating or rollingCan be shaped by beating or rolling Are ductileAre ductile
Can be drawn into a wireCan be drawn into a wire Exhibit a range of melting temperatures and Exhibit a range of melting temperatures and
relatively high boiling temperaturesrelatively high boiling temperatures Generally have high densitiesGenerally have high densities Are lustrous or reflective (shiny)Are lustrous or reflective (shiny) Are often hard, with high tensile strengthAre often hard, with high tensile strength
What is the differences between the metals and non-metals?
ExceptionsExceptions
Not all metals have Not all metals have allall of these properties. of these properties. Mercury is a liquid at room temperature Mercury is a liquid at room temperature
meaning it has an unusually low melting meaning it has an unusually low melting temperature. temperature.
Chromium is brittle rather than malleable, Chromium is brittle rather than malleable, meaning it breaks rather easily.meaning it breaks rather easily.
Group one metals as you have seen are softGroup one metals as you have seen are soft These elements however exhibit These elements however exhibit mostmost of of
the properties and are classified as metalsthe properties and are classified as metals
Your TurnYour Turn
Page 80 of text.Page 80 of text. Questions 2 and 3Questions 2 and 3
Properties and StructureProperties and Structure
Each of the properties of metals Each of the properties of metals gives us some information about a gives us some information about a metals structure.metals structure.
Can you make any inferences about Can you make any inferences about the structure of metals.the structure of metals.
For ExampleFor Example
Clues from the PropertiesClues from the Properties It is reasonable to assume from those two It is reasonable to assume from those two
tables thattables that The atoms in metals are not uncharged.The atoms in metals are not uncharged. As solid metals are particular shapes and do not As solid metals are particular shapes and do not
spontaneously change shape the atoms cannot spontaneously change shape the atoms cannot move around.move around.
They must be able to move however when They must be able to move however when beaten as metals are malleable and ductile.beaten as metals are malleable and ductile.
They must have strong forces between particles.They must have strong forces between particles. The charged particles must be able to move The charged particles must be able to move
among the atoms and pass on energy.among the atoms and pass on energy. So how are these particles arranged?So how are these particles arranged?
MetalsMetals
Most metals have only one or two Most metals have only one or two electrons in their outer shell. electrons in their outer shell.
It is relatively easy for another It is relatively easy for another particle to draw the valence particle to draw the valence electrons away from a metal atom.electrons away from a metal atom.
This is due to most metals having a This is due to most metals having a low first ionization energy.low first ionization energy.
Lets consider uncharged Lets consider uncharged sodiumsodium
1s1s222s2s222p2p663s3s11
The valence electron is held very weakly The valence electron is held very weakly as it is further from the nucleus than the as it is further from the nucleus than the 10 inner shell electrons.10 inner shell electrons.
If sodium was by itself the electron would If sodium was by itself the electron would remain in place orbiting sodium.remain in place orbiting sodium.
But if a sodium atom was surrounded on But if a sodium atom was surrounded on all sides by other sodium atoms, the all sides by other sodium atoms, the valence electron, which is on the surface valence electron, which is on the surface of the atom, will experience some of the atom, will experience some attraction from the positively charged attraction from the positively charged nuclei of the surrounding nuclei.nuclei of the surrounding nuclei.
SodiumSodium1s1s222s2s222p2p663s3s11
It makes sense then that the valence It makes sense then that the valence electron on each sodium atom present electron on each sodium atom present would be drawn in to the space between would be drawn in to the space between atoms by the combined attractive forces.atoms by the combined attractive forces.
Once in between atoms it will be moving Once in between atoms it will be moving about constantly between all the positively about constantly between all the positively charged sodium atoms so it will no longer charged sodium atoms so it will no longer remain in the locality of the atom it came remain in the locality of the atom it came from.from.
When Sodium Atoms When Sodium Atoms MeetMeet
The metallic latticeThe metallic lattice
The electrons that are detached from The electrons that are detached from their atoms are called their atoms are called delocalised delocalised electronselectrons. .
But what about the sodium atom?But what about the sodium atom? We now have a large set of atoms that We now have a large set of atoms that
have lost an electron. They each have a have lost an electron. They each have a net charge of 1+, since they still have 11 net charge of 1+, since they still have 11 protons but only 10 electrons. protons but only 10 electrons.
They are now positively charged sodium They are now positively charged sodium ions or sodium cations.ions or sodium cations.
The Metallic Bonding ModelThe Metallic Bonding Model Chemists believe that, in a solid sample of Chemists believe that, in a solid sample of
metal:metal: Positive ions are arranged in a closely packed Positive ions are arranged in a closely packed
structure. This structure is described as a structure. This structure is described as a three-three-dimensional latticedimensional lattice of fixed of fixed cationscations..
The smaller negatively charged valence electrons The smaller negatively charged valence electrons are free to move throughout the lattice. These are free to move throughout the lattice. These electrons are called electrons are called delocalised electronsdelocalised electrons because they belong to the lattice as a whole.because they belong to the lattice as a whole.
The inner shell electrons are localised and not The inner shell electrons are localised and not free moving.free moving.
Electrostatic ForcesElectrostatic Forces
The ions are held in the lattice by the The ions are held in the lattice by the electrostatic forceelectrostatic force of attraction between of attraction between them and the delocalised electrons. This them and the delocalised electrons. This attraction extends throughout the lattice attraction extends throughout the lattice and is called and is called metallic bondingmetallic bonding..
Electrostatic forces are the forces between Electrostatic forces are the forces between particles that are caused by their electric particles that are caused by their electric charges. charges.
How do the forces affect the How do the forces affect the structure?structure?
A lot of pushing and pulling in this mixture of A lot of pushing and pulling in this mixture of positively charged cations and negatively positively charged cations and negatively charged delocalised electrons. Why?charged delocalised electrons. Why?
This occurs until the sodium ions settle into a This occurs until the sodium ions settle into a stable arrangement. stable arrangement.
It is stable when the force of attraction It is stable when the force of attraction between the sodium ions and delocalised between the sodium ions and delocalised electrons is maximised and the force of electrons is maximised and the force of repulsion between the sodium ions is repulsion between the sodium ions is minimised. minimised.
Lattice?Lattice?
In solid crystals of sodium there are In solid crystals of sodium there are billions of sodium ions.billions of sodium ions.
For each sodium ion there is how many For each sodium ion there is how many delocalised electrons?delocalised electrons?
The positive sodium ions are in a highly The positive sodium ions are in a highly organised geometric arrangement with the organised geometric arrangement with the negatively charged delocalised electrons negatively charged delocalised electrons moving rapidly between the ions.moving rapidly between the ions.
This structure is termed a metallic lattice. This structure is termed a metallic lattice. The delocalised electrons in a metallic The delocalised electrons in a metallic
lattice are often referred to as a ‘sea of lattice are often referred to as a ‘sea of valence electrons’valence electrons’
The Metal The Metal Lattice of Lattice of SodiumSodium
Explaining the Properties of Explaining the Properties of MetalsMetals
We can now explain why metals exhibit We can now explain why metals exhibit some of the properties we have discussed.some of the properties we have discussed.
As they are highly mobile particles, the As they are highly mobile particles, the delocalised electrons can very rapidly delocalised electrons can very rapidly transfer energy from one end of the metal transfer energy from one end of the metal to the other. to the other.
Since they are charged they can also Since they are charged they can also transfer electrical energy. transfer electrical energy.
The electrons that are present in the The electrons that are present in the surface of the metal are excellent surface of the metal are excellent reflectors of light, so they are responsible reflectors of light, so they are responsible for the lustre shown by metals.for the lustre shown by metals.
Your TurnYour Turn
Page 82.Page 82. Question 5Question 5
Explaining the Properties of Explaining the Properties of MetalsMetals
Metals are MalleableMetals are Malleable
Conducting HeatConducting Heat
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Conducting ElectricityConducting Electricity
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Metals are lustrousMetals are lustrous
Limitations of the Metallic Limitations of the Metallic Bonding ModelBonding Model
Some things cannot be explained by the metal Some things cannot be explained by the metal model.model. The range of melting temperatures and densities of The range of melting temperatures and densities of
different metals.different metals. The differences in electrical conductivity between The differences in electrical conductivity between
metals.metals. The magnetic nature of metals such as cobalt, iron, The magnetic nature of metals such as cobalt, iron,
and nickel.and nickel. They model cannot be drawn to scale.They model cannot be drawn to scale. Metal ions are not solid balls, any more than atoms are. Metal ions are not solid balls, any more than atoms are.
Nor are they coloured. Infact ions are pretty much Nor are they coloured. Infact ions are pretty much empty space.empty space.
Delocalised electrons move throughout the structure Delocalised electrons move throughout the structure extremely rapidly, we cannot show this in a model.extremely rapidly, we cannot show this in a model.
The electrostatic forces cannot be seen.The electrostatic forces cannot be seen.
Your TurnYour Turn
Page 82Page 82 Question 6Question 6
Modifying MetalsModifying Metals Few metals used are in their pure form.Few metals used are in their pure form. Most metals used need to be modified in Most metals used need to be modified in
order to produce the desired properties for order to produce the desired properties for particular uses. particular uses. Pure iron is not hard enough, so it is converted Pure iron is not hard enough, so it is converted
to steel by mixing it with 2% carbon.to steel by mixing it with 2% carbon. The properties of metals are altered by The properties of metals are altered by
adding small amounts of another adding small amounts of another substance. The substances are melted substance. The substances are melted together, mixed and allowed to cool. together, mixed and allowed to cool.
These mixtures are called alloys.These mixtures are called alloys. There are two main types of alloys.There are two main types of alloys.
Substitutional AlloysSubstitutional Alloys Substitutional alloys are made from elements that have Substitutional alloys are made from elements that have
fairly similar chemical properties and atoms of similar size. fairly similar chemical properties and atoms of similar size. Our coins are made from an alloy that is 75% copper and Our coins are made from an alloy that is 75% copper and
25% nickel.25% nickel. The nickel atoms take the place of some copper atoms in The nickel atoms take the place of some copper atoms in
the lattice. the lattice. Both the nickel and copper ions are attracted to the sea of Both the nickel and copper ions are attracted to the sea of
electrons so the lattice is held strongly in place.electrons so the lattice is held strongly in place. Due to the slight difference in the size of the atoms there is Due to the slight difference in the size of the atoms there is
a restriction when the layers within the lattice move a restriction when the layers within the lattice move relative to one another. This makes the alloy harder and relative to one another. This makes the alloy harder and less malleable.less malleable.
Interstitial AlloysInterstitial Alloys A small proportion of an element with significantly smaller A small proportion of an element with significantly smaller
atoms is added to a metal. atoms is added to a metal. Carbon can be added to iron to increase its hardness. The Carbon can be added to iron to increase its hardness. The
resulting product is called steel.resulting product is called steel. In steel, the smaller carbon atoms fit randomly in the In steel, the smaller carbon atoms fit randomly in the
hollows between the packed metal ions. hollows between the packed metal ions. Like substitutional alloys the presence of different atoms Like substitutional alloys the presence of different atoms
makes it difficult for layers of the lattice to slide past one makes it difficult for layers of the lattice to slide past one another. Making it less malleable than pure iron.another. Making it less malleable than pure iron.
Common AlloysCommon Alloys
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Page 89Page 89 Question 7Question 7
Work Hardening and Heat Work Hardening and Heat TreatmentTreatment
The way a metal has been prepared The way a metal has been prepared will also affect how it behaves.will also affect how it behaves.
Many metals are prepared in a liquid Many metals are prepared in a liquid state and then cooled.state and then cooled.
The rate at which a metal is cooled The rate at which a metal is cooled has significant effect on the has significant effect on the properties of the solid.properties of the solid.
Metal CrystalsMetal Crystals A crystal is a region in a solid in which the A crystal is a region in a solid in which the
particles are arranged in a regular way. particles are arranged in a regular way. A sample of solid metal, however consists A sample of solid metal, however consists
of a large number of small crystals.of a large number of small crystals.
At the point where At the point where one crystal meets one crystal meets another, the another, the regular lattice is regular lattice is disrupted.disrupted.
Galvanised IronGalvanised Iron
Figure 5.17(b)Figure 5.17(b) This piece of This piece of steel (an alloy of iron, steel (an alloy of iron, chromium and molybdenum) chromium and molybdenum) has individual crystals that has individual crystals that formed as the molten metal formed as the molten metal mixture cooled down.mixture cooled down.
So who cares about crystalsSo who cares about crystals
The way a metal behaves, its malleability The way a metal behaves, its malleability and its brittleness, will depend to some and its brittleness, will depend to some extent on the size of these crystals and the extent on the size of these crystals and the way they are arranged.way they are arranged.
The smaller the crystals the harder the The smaller the crystals the harder the metal, as there will be less free movement metal, as there will be less free movement of layers of ions over each other.of layers of ions over each other.
Smaller crystals, however, also mean more Smaller crystals, however, also mean more areas of disruption between them and this areas of disruption between them and this usually means the metal will be more brittle.usually means the metal will be more brittle.
Figure 5.18 Figure 5.18 In these representations of a metal, each circle In these representations of a metal, each circle represents an ion. (a) A solid crystalline metal; (b) A molten represents an ion. (a) A solid crystalline metal; (b) A molten metal with a random arrangement of ions.metal with a random arrangement of ions.
Solid Molten
Work HardeningWork Hardening
Working (hammering) cold metals causes Working (hammering) cold metals causes a rearrangement of crystal grains and a a rearrangement of crystal grains and a hardening of the metal. hardening of the metal.
Try bending a paper clip. Bend it once and Try bending a paper clip. Bend it once and it remains fairly pliable, keep bending it it remains fairly pliable, keep bending it and it snaps. and it snaps.
Bending or working metal causes the Bending or working metal causes the crystal grains to be rearranged making the crystal grains to be rearranged making the metal harder but more brittle.metal harder but more brittle.
Heat Treatment.Heat Treatment.
Your TurnYour Turn
Question 8 on Page 89.Question 8 on Page 89.
The question regarding metals from The question regarding metals from your resource manual.your resource manual.