Doc Brown's Chemistry GCSE 9-1, IGCSE, O Level Chemistry Revision Notes

Sub-index of links for this GCSE/IGCSE TRANSITION METALS page

1. Where are the Transition Metals Series in the Periodic Table?

3. Physical properties of transition Metals: strength, melting/boiling points, density

4. The chemical properties and reactions of transition metals

4a. Transition metals form coloured compounds and ions in solution

4b. Some other odd bits of transition metal chemistry

5. Use of transition metals or their compounds as catalysts

7. Note on uses of other non–transition metals/alloys e.g. aluminium/duralumin

8. More on iron and steel and examples of how metals can be made more useful

10. Transition Metals and Use in Superconductors

11. More on making metals more useful? e.g. alloys of  iron, aluminium & titanium

See also RUSTING-CORROSION, PREVENTION, and an introduction to OXIDATION and REDUCTION

GCSE/IGCSE/O Level multiple choice QUIZ on Transition Metals

Advanced A Level Chemistry Notes on the 3d block & Transition Metals

Keywords: Actually 1 scandium and 10 zinc are not really proper transition metals, they are not very 'colourful' in their chemistry!, they only form one colourless ion and are not noted for their catalytic activity, a bit dull really!, but zinc is a useful metal as are all the true transition metals titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper! The physical properties of Transition Metals like density, melting points, boiling points, strength are described and discussed along with a description of the important transition metal chemical properties of e.g. titanium, vanadium, manganese, iron, cobalt, nickel, copper and zinc. There are also sections on how transition metals can be improved to increase their usefulness e.g. alloys and they are compared with the important 'non–transition' metals like aluminium, tin and lead. These notes on transition metals describing their physical properties, chemical reactions and uses are designed to meet the highest standards of knowledge and understanding required for students/pupils doing GCSE chemistry, IGCSE chemistry, O Level chemistry, KS4 science courses and a basic primer for an advanced level chemistry courses (see A Level links).  These revision notes on the alkali metals should prove useful for the new AQA, Edexcel and OCR GCSE (9–1) chemistry science courses., but look for separate links for A level students (see below and near the bottom of the page) Revision notes on the physical and chemical properties of transition metals help when revising for AQA GCSE chemistry, Edexcel GCSE chemistry, OCR GCSE gateway science chemistry, OCR 21st century science chemistry revising with GCSE 9-1 chemistry examination questions

1. Some Reminders about the Periodic Table by way of an introduction

The basic structure of the Periodic Table and note where the 'Transition Metals' are

• Reminders on the periodic table and where you find transition metals.
• The elements are laid out in order of Atomic Number
• Hydrogen, 1, H, does not readily fit into any group
• A Group is a vertical column of like elements e.g. Group 1 The Alkali Metals (Li, Na, K etc.), Group 7 The Halogens (F, Cl, Br, I etc.) and Group 0/8 The Noble Gases (He, Ne, Ar etc.). The group number equals the number of electrons in the outer shell (e.g. chlorine's electron arrangement is 2.8.7, the second element down in Group 7).
• A Period is a complete horizontal row of elements with a variety of properties (more metallic to more non–metallic from left to right). All the elements use the same number of electron shells which equals the period number (e.g. sodium's electron arrangement 2.8.1, the first element in Period 3).
• Metals tend to be on the left and in the middle of the periodic table and the transition metals are no exception.
• On Period 4 is a horizontal row of ten elements between Group 2 and Group 3, and these elements from Sc to Zn are called the 1st Transition Metals Series of Elements ...
  • The transition metals occupy the bottom–middle part of the Periodic Table above, and just the first series are shown in the above diagram.
  • Many of them by name and their uses should be quite familiar to you e.g. titanium, iron, nickel and copper.
  • Directly below them, but not shown, the further 2nd and 3rd transition metal series,
  • so the Transition Metals Series are just a horizontal section of a period ie a block of elements, in the middle of the Periodic Table.
  • Look out in particular for the physical properties, chemical reactions and uses of ...
    • ... chromium Cr, manganese Mn, iron Fe, cobalt Co, nickel Ni and copper Cu.

1. True transition metals usually form many coloured ion compounds (e.g. blue copper salt solutions) and are used in paint pigments, pottery glazes, stained glass windows and you observe weathered copper roofs turn green! Iron(III) oxide has been used from prehistoric times as a red-brown pigment (red ochre).
   • The colour usually originates from a transition metal ion in the compound e.g.
2. Many transition metals e.g. iron and platinum are used as catalysts.
   • Many transition metal compounds also show catalytic activity.
3. True transition metals have variable valencies (numerical combining power with other elements) giving rise to different formulae when combined with same elements.
   • e.g. iron forms three oxides, FeO, Fe₂O₃ and Fe₃O₄, copper forms two, Cu₂O and CuO,
   • scandium only forms one, Sc₂O₃ and zinc one, ZnO, and neither scandium nor zinc give coloured compounds due to their metal ions (Sc³⁺ and Zn²⁺), and neither do they show any real potential catalytic activity, so scandium and zinc are NOT true transition metals.
4. You should also know they are often dense and have higher melting points compared to other metals.

• Pd

  metals

  horizontal series of metals

  metal ==> non–metal groups

  Gp1

  Gp2

  Gp3

  Gp4

  Gp5

  Gp6

  Gp7

  Gp0

  1

  He

  2

  Li

  Be

  a short section of the periodic table showing the 1st series of transition metals

  B

  C

  N

  O

  F

  Ne

  3

  Na

  Mg

  Al

  Si

  P

  S

  Cl

  Ar

  4

  K

  Ca

  21Sc

  22Ti

  23V

  24Cr

  25Mn

  26Fe

  27Co

  28Ni

  29Cu

  30Zn

  Ga

  Ge

  As

  Se

  Br

  Kr

   
• Comparison of Transition Metals and Group 1 Alkali Metals
  • (see section of periodic table above)
  • By the time you have reached the study of transition metals, you will have already studied the very reactive group 1 alkali metals with their relatively uncharacteristic physical properties.
  • So its useful to highlight some of these differences.
    • Transition metals have much higher melting points than group 1 elements - stronger metallic atomic bonding (except mercury).
    • Transition metals have higher densities than group 1 alkali metals, non of them float on water!
    • Transition metals are stronger and harder than group 1 metals - again due to stronger metallic bonding
    • Transition metals are less reactive than group 1 alkali metals towards oxygen, water and halogens like chlorine.
    • Group 1 Alkali Metals rapidly react with water and even more energetically with acids!
    • Transition metals do not react as quickly with water or oxygen so do not corrode as quickly.
    • Many transition metals will react slowly with acids, unlike the more reactive Group 2 metals like magnesium for example.
    • Transition metals form coloured ions with different charges, hence different coloured compounds (eg blue copper sulfate solution, brown iron oxide rust etc.).
      • Group 1 alkali metals have only one outer electron, that is easily lost, and so form only one stable ion and they are colourless ions (think of the salt sodium chloride, a typical colourless compound).
      • Transition metals have more than one electron in the outer shell and more of these electrons can be involved in bonding e.g. forming 2+ and 3+ ions and more complicated ions like MnO₄^- etc., so the chemistry of transition metals is much more complicated - more diverse colourful ions and more interesting!
    • Scandium and zinc are not true transition metals e.g. they don't form coloured compounds or different compounds with the same element like Ti to Cu do, but they are not chemically related to group 1 alkali metals.

(3a) Some General Physical Properties Characteristic of Transition Metals

• Generally speaking transition metals are hard, tough and strong (compared with the 'soft' Group 1 Alkali metals!) because of the strong metallic atom–atom bonding.

• Transition metals are good conductors of heat and electricity (there have many free electrons per atom to carry thermal or electrical energy ).

  • Transition metals are easily hammered and bent into shape (malleable).

  • Transition metals can be drawn out into strong wire (ductile).

  • Transition metals are typically lustrous/shiny solids.

(3b) Transition metals have High Melting Points and Boiling Points

• The bonding between the atoms in transition metals is very strong (see metallic bonding notes).
  • The strong attractive force between the atoms is only weakened at high temperatures, hence the high melting points and boiling points (again this contrasts with Group 1 Alkali Metals).
• Mercury is in another transition metal (actually in the 3rd series of transition metals), but unusually, it has a very low melting point of –39^oC.
• More typically, for example: iron melts at 1535°C and boils at 2750°C BUT a Group 1 Alkali Metal such as sodium melts at 98°C and boils at 883°C.

(3c) High density

• Another consequence of the strong bonding between the atoms in transition metals is that they are tightly held together to give a high density.
• For example: iron has a density of 7.9 g/cm³ and sodium has a density of 0.97 g/cm³(and floats on water while fizzing! water has a density of 1.0 g/cm³).

4. THE CHEMISTRY OF TRANSITION METALS

Their chemical properties and chemical reactions

4a. Transition metals form coloured compounds and ions in solution

There are several important chemical characteristics of transition metals you should be very aware of.

(i) True transition metals form at least two different coloured ions, so at least two series of compounds such as oxides, sulfates or chlorides can be prepared.

You find the colours in many gem stones are due to transition metal ions/compounds in these naturally occurring minerals e.g. aquamarine is blue due to iron compounds, green emeralds due to iron and titanium ions, red and blue sapphires owe their different colours to traces of iron, titanium, chromium and copper ions/compounds, deep red garnets due to iron compounds, red rubies due to chromium compounds.

You see the green colour of copper compounds on weathered copper roofs.

Iron compounds are often green, orange or brown. e.g. rust is a red–brown hydrated oxide of iron.

The best examples are the stained glass windows in many churches, some glass colours go back over 1000 years in some medieval stained glass windows.

Copper compounds are often green or blue e.g. copper carbonate or copper sulfate crystals.

Transition metals can have ions with at least two different charges because different numbers of their outer electrons can be involved in bonding e.g. iron can lose two or three electrons quite easily to form compounds and maybe with the same elements.

This means they can form two or more series of compounds with the same negative ion e.g.

(i) with oxide O^2- and Cu⁺ and Cu²⁺ ions: copper(I) oxide Cu₂O (brown) and copper(II) oxide, CuO (black)

Note that the two different compounds have different colours.

(ii) with sulfate SO₄^2- and Fe²⁺ and Fe³⁺ ions: iron(II) sulfate, FeSO₄ and iron(III) sulfate Fe₂(SO₄)₃

The compounds are green and brown respectively.

(iii) with oxide O^2- and Fe²⁺ and Fe³⁺ ions: iron(II) oxide FeO and iron(III) oxide, Fe₂O₃

(ii) Transition metals and their compounds often have good catalytic properties (see section (e) for lots of examples e.g. iron catalyst in the Haber synthesis of ammonia.

They tend to be much less reactive than the Alkali Metals.

Transition metals do not react as quickly with water or oxygen so do not corrode as quickly.

Many transition metals will react slowly with acids, unlike magnesium for example.

Transition metals tend to form more coloured ions and compounds more than most other elements either in solid form or dissolved in a solvent like water.

Examples of the colours of some transition metal salts in aqueous solution are shown below (grey = colourless in the diagrams).

These transition metal  coloured ions/compounds often have quite a complex structure and indeed are called complexes.

1. Sc – scandium salts, such as the chloride, ScCl_3, are colourless and are not typical of transition metals
   • Scandium isn't really a transition metal, but don't worry about it!
2. Ti – titanium(IV) chloride, TiCl₃, is purple
3. V – vanadium(III) chloride, VCl₃, is green
4. Cr – chromium(III) sulfate, Cr₂(SO₄)₃, is dark green (chromate(VI) salts are yellow, dichromate(VI) salts are orange)
   • chromium forms two positive ions, Cr²⁺ (blue) and Cr³⁺ (green)
   • and two coloured negative ions, CrO₄^2– (yellow) and dichromate Cr₂O₇^2– (orange)
5. Mn – manganese compounds
   •  –  potassium manganate(VII), KMnO₄, is purple, due to the purple MnO₄^– ion
   • manganese(II) salts eg MnCl₂ are pale pink, it is the Mn²⁺ ion which is a pale pink.
6. Fe – iron(III) chloride, FeCl₃, is yellow–orange–brown.
   • Iron(II) compounds are usually light green and iron(III) compounds orange–brown.
   • Some iron compounds are blood red in colour e.g. the oxygen carrying haemoglobin molecule in your blood stream!

     • e.g. the iron(II) ion Fe²⁺ (pale green) in iron(II) sulfate FeSO₄

     • and the iron(III) ion Fe³⁺ (orange–brown) in iron(III) chloride solution FeCl₃(aq)

     • There is another chloride, iron(II) chloride FeCl₂,

     • and there are three oxides, FeO (very unstable), Fe₂O₃ (rust, haematite ore) and Fe₃O₄ (magnetite ore)

7. Co – cobalt sulfate, CoSO₄, is pinkish, it is the Co²⁺ ion that is pink, cobalt also forms a Co³⁺ ion of different colour.
8. Ni – nickel chloride, NiCl₂, is green, its the Ni²⁺ ion that is green in solution.
9. Cu – copper(II) sulfate, CuSO₄, is blue, its the Cu²⁺ ion that is blue in solid crystals and in solution.
   • Most common copper compounds are blue in their crystals or solution and sometimes green.
   • The blue aqueous copper ion, Cu²⁺_(aq), actually has a more complicated structure:
     • *[Cu(H₂O)₆]²⁺_(aq) and when excess ammonia solution is added,
     • after the initial gelatinous blue copper(II) hydroxide precipitate is formed, Cu(OH)₂,
     • it dissolves to form the deep royal blue ion: *[Cu(H₂O)₂(NH₃)₄]²⁺_(aq).
     • *are called complex ions and when coloured are typical of transition metal chemistry.
   • Copper(II) oxide, CuO, black insoluble solid, readily dissolving in acids to give soluble blue salts e.g.
     • copper(II) sulfate, CuSO₄, from dilute sulfuric acid,
     • copper(II) nitrate, Cu(NO₃)₂, from dilute nitric acid
     • and greeny–blue copper(II) chloride, CuCl₂, from dilute hydrochloric acid.
   • Copper(II) hydroxide, Cu(OH)₂, blue gelatinous precipitate formed when alkali added to copper salt solutions.
   • Copper(II) carbonate, CuCO₃, is turquoise–green insoluble solid, readily dissolving in acids, evolving carbon dioxide, to give soluble blue salts (see above)
   • Copper's valency or combining power is usually two e.g. compounds containing the Cu²⁺ ion.
     • However there are copper(I) compounds where the valency is one containing the Cu⁺ ion.
     • This variable valency, hence compounds of the same elements, but with different formulae, is typical of transition metal compounds e.g.
     • copper(I) oxide, Cu₂O, an insoluble red–brown solid (CuO is black),
     • or copper(I) sulfate, Cu₂SO₄, a white solid (crystals of CuSO₄ are blue).
10. Zn – zinc salts such as zinc sulfate, ZnSO₄, are usually colourless and are not typical of transition metals.
    • Zinc isn't really a transition metal, but don't worry about it!

• See Acids, Bases and Salts page for the preparation of Transition Metal Salts from insoluble oxides, hydroxides or carbonates (insoluble bases).

• Many of the transition metal carbonates are unstable on heating and readily undergo thermal decomposition.

  • metal carbonate ==> metal oxide + carbon dioxide

  • e.g.

  • copper(II) carbonate ==> copper(II) oxide + carbon dioxide

    • CuCO_3(s) ==> CuO_(s) + CO_2(g)

  • or

  • zinc carbonate ==> zinc oxide + carbon dioxide

    • ZnCO_3(s) ==> ZnO_(s) + CO_2(g)

  • In general the equation is ...

  • MCO_3(s) ==> MO_(s) + CO_2(g) where M could be Fe, Cu, Mn or Zn

  • The carbon dioxide can be confirmed by giving a white milky precipitate with limewater.

  • Sometimes the two solids show a colour change eg

    • for M = Cu: turquoise green carbonate ==> black copper(II) oxide

    • for M = Zn: white carbonate ==> white zinc oxide, but yellow hot

• Many transition metal ions (e.g. in soluble salt solutions) give coloured hydroxide precipitates when mixed with aqueous sodium hydroxide solution. However, zinc ions give a white hydroxide precipitate

  • These reactions can be used to help identify transition metal ions in solution.

  • A precipitation reaction happens when two solutions (of soluble substances) are mixed together and a solid product (insoluble) precipitates out of the mixed solution.

• transition metal salt solution + sodium hydroxide solution ==> solid hydroxide precipitate + sodium salt left in solution

• ionically the precipitation reactions are:

  • metal ion + hydroxide ion ==> hydroxide precipitate

  • (1) iron(II) ion Fe²⁺, pale green in aqueous solution,

    • which gives a dark grey–green gelatinous precipitate of iron(II) hydroxide with sodium hydroxide solution

    ,

    • iron(II) sulfate + sodium hydroxide ==> iron(II) hydroxide + sodium sulfate

      • FeSO₄(aq) + 2NaOH(aq) ==> Fe(OH)₂(s) + Na₂SO₄(aq)

    • or

    • iron(II) chloride + sodium hydroxide ==> iron(II) hydroxide + sodium chloride

      • FeCl₂(aq) + 2NaOH(aq) ==> Fe(OH)₂(s) + 2NaCl(aq)

    • For these reactions the ionic equation is ..

      • Fe²⁺_(aq) + 2OH^–_(aq) ==> Fe(OH)₂(s)

  • (2) iron(III) ion Fe³⁺:

    • giving a brown iron(III) hydroxide precipitate with sodium hydroxide solution,

    • iron(III) chloride + sodium hydroxide ==> iron(III) hydroxide + sodium chloride

      • FeCl₃(aq) + 3NaOH(aq) ==> Fe(OH)₃(s) + 3NaCl(aq)

    • the ionic equation is ...

      • Fe³⁺(aq) + 3OH^–(aq) ==> Fe(OH)₃(s)

  • (3) copper(II) ion Cu²⁺, blue in aqueous solution,

    • which gives a blue copper(II) hydroxide precipitate with sodium hydroxide solution.

    • copper(II) sulfate + sodium hydroxide ==> copper(II) hydroxide + sodium sulfate

      • CuSO₄(aq) + 2NaOH(aq) ==> Cu(OH)₂(s) + Na₂SO₄(aq)

    • or

    • copper(II) chloride + sodium hydroxide ==> copper(II) hydroxide + sodium chloride

      • CuCl₂(aq) + 2NaOH(aq) ==> Cu(OH)₂(s) + 2NaCl(aq)

    • For these two reactions the ionic equation is ..

    • Cu²⁺_(aq) + 2OH^–_(aq) ==> Cu(OH)₂(s)

    • Note that the copper ion can be also detected by its flame colour of green–blue.

      • The flame test is conducted by dipping a nichrome (cheap)/platinum (expensive) wire into a copper salt solution and placing the end of the wire plus drop into the hottest part of a roaring bunsen flame when you see flashes of blue and green colour.

        • Summary of flame tests

  • (4) zinc ion Zn²⁺, colourless in aqueous solution,

    • which gives a white zinc hydroxide precipitate with sodium hydroxide solution.

    • zinc sulfate + sodium hydroxide ==> zinc hydroxide + sodium sulfate

      • ZnSO₄(aq) + 2NaOH(aq) ==> Zn(OH)₂(s) + Na₂SO₄(aq)

    • For this reaction the ionic equation is ..

    • (4a)  Zn²⁺_(aq) + 2OH^–_(aq) ==> Zn(OH)₂(s)

    • However, unlike the other precipitates described above, zinc hydroxide dissolves if excess sodium hydroxide solution is added i.e. add a lot more and the result is a clear colourless solution of another zinc compound formed by the extra hydroxide ions reacting with the zinc hydroxide.

    • (4b)  Zn(OH)_2(s) + 2OH^–(aq) ==> Zn(OH)₄]^2–_(aq)

  • The above four hydroxide precipitate reactions are illustrated in the diagram below.

• These transition metal hydroxide precipitates are basically solids, but of a somewhat gelatinous nature because they incorporate lots of  water in their structure.

• The above coloured hydroxide precipitates contrast with the white hydroxide precipitates given by some non–transition metal ions e.g.

  • magnesium salt + sodium hydroxide ==> white precipitate of magnesium hydroxide

    • ionic equation: Mg²⁺(aq) + 2OH^–(aq) ==> Mg(OH)₂(s)

      • The observations would correspond with 4a only in the diagram above

  • calcium salt + sodium hydroxide ==> white precipitate of calcium hydroxide

    • ionic equation: Ca²⁺(aq) + 2OH^–(aq) ==> Ca(OH)₂(s)

      • The observations would correspond with 4a only in the diagram above

  • aluminium salt + sodium hydroxide ==> white precipitate of aluminium hydroxide

    • ionic equation: Al³⁺(aq) + 3OH^–(aq) ==> Al(OH)₃(s)

      • Aluminium hydroxide dissolves in excess sodium hydroxide to give a clear colourless solution, but magnesium hydroxide and calcium hydroxide do not behave in this way.

        • The observations would correspond with 4a plus 4b in the diagram above

• Also note that iron has two valencies or combining power giving different compound formulae. Multiple valency, hence multiple compound formation, is another characteristic (but not unique) feature of transition metal chemistry.

  • The valency of chlorine is 1 and iron can have a combining power of 2 (II) or 3 (III).

  • FeCl₂ iron(II) chloride (once called ferrous chloride)

  • FeCl₃ iron(III) chloride (once called ferric chloride)

    • The number in Roman numerals is the valency or combining power e.g.

    • oxygen's valency is 2 and copper, another transition element, has a valency of 1 (I) or 2 (II)

    • so we have Cu₂O copper(I) oxide (once called cuprous oxide)

      • and CuO copper(II) oxide (once called cupric oxide).

        • hence the need for the valency of the metal of the metal to be shown in Roman numerals.

• There are more details and more tests on the Chemical Identification page (use the alphabetical list at the top).

• The coloured nature of many transition metal compounds also shows up in the thermal decomposition of the transition metal carbonates e.g.

  • copper(II) carbonate_{(s, green)}  ==> copper(II) oxide_{(s, black)}  + carbon dioxide_(g)

    • CuCO₃ ==> CuO + CO₂

    • CuCO₃(s) ==> CuO(s) + CO₂(g)   (symbol equation with state symbols)

    • The colour change from the dark green copper carbonate to the jet black copper oxide is clearly observed.

  • iron(II) carbonate_{(s, dark green)}  ==> iron(II) oxide_{(s, black)}  + carbon dioxide

    • FeCO₃ ==> FeO + CO₂

    • FeCO₃(s) ==> FeO(s) + CO₂(g)   (symbol equation with state symbols)

    • The colour change is from a dark green reactant to a black solid residue.

  • manganese(II) carbonate_{(s, pale pink)}  ==> manganese(II) oxide_{(s, white)}  + carbon dioxide

    • MnCO₃ ==> MnO + CO₂

    • MnCO₃(s) ==> MnO(s) + CO₂(g)   (symbol equation with state symbols)

    • The colour change is from a pale pink solid to a white solid residue.

  • However, this no colour change for zinc carbonate, which is, as mentioned before, NOT a typical transition metal.

  • zinc carbonate_{(s, white)}  ==> zinc oxide_{(s, yellow hot, white cold)}  + carbon dioxide

    • ZnCO₃ ==> ZnO + CO₂

    • ZnCO₃(s) ==> ZnO(s) + CO₂(g)   (symbol equation with state symbols)

    • Both the zinc carbonate and zinc oxide are white, but zinc oxide turns yellow when very hot, on cooling at the end of the experiment in turns white.

• Many transition metals are used directly as catalysts in industrial chemical processes and in the anti–pollution catalytic converters in car exhausts.
• For example iron catalysts are used in the HABER PROCESS for the synthesis of ammonia:
  • Nitrogen + Hydrogen ==> Ammonia (via a catalyst of Fe atoms)
  • or N_2(g) + 3H_2(g) ==> 2NH_3(g) 
• Platinum and rhodium (in other transition series below Sc–Zn) are used in the catalytic converters in car exhausts to reduce the emission of carbon monoxide and nitrogen monoxide, which are converted to the non–polluting gases nitrogen and carbon dioxide.
• 2NO_(g) + 2CO_(g) ==> N_2(g) + 2CO_2(g)
• Nickel is the catalyst for 'hydrogenation' in the margarine industry. It catalyses the addition of hydrogen to an alkene carbon = carbon double bond (>C=C< + H₂ ==> >CH–CH<) Note the > and < just indicate the other bonds from carbon.
  • This process converts unsaturated vegetable oils into higher melting saturated fats which are more 'spreadable' with a knife!

5b. Some compounds of transition metals are also used as catalysts

• As well as the metals, the compounds of transition metals also acts as catalysts.
• EXAMPLES
  • For example manganese dioxide (or manganese(IV) oxide), MnO₂, a black powder, readily decomposes an aqueous solution of hydrogen peroxide:
    • Hydrogen peroxide ==> water + oxygen
      • 2H₂O_2(aq) ==> 2H₂O_(l) + O_2(g)
    • A useful reaction in the laboratory for preparing oxygen gas.
  • Vanadium(V) oxide (vanadium pentoxide, V₂O₅) is used as the catalyst for converting sulfur dioxide into sulfur trioxide as a stage in the manufacture of sulfuric acid in the CONTACT PROCESS.
    • 2SO_2(g) + O_2(g) ==> 2SO_3(g)   (via V₂O₅ catalyst)
    • A very important industrial process because sulfuric acid is a widely used chemical in industry.

• Alloys are very useful materials and most metals in everyday use are alloys. However pure copper, gold, iron (three transition metals) and aluminium (non-transition metal) are too soft for many uses and so are mixed with other metals, converting them to alloys, and making them harder for everyday use.

• Bronze is an alloy of copper (transition metal) and tin (non-transition metal) and is used to make statues and decorative objects. Brass is a hard wearing alloy of copper and zinc and used to make water taps, and door fittings (e.g. door knobs). Gold used as jewellery is usually an alloy with silver (another transition metal), copper and zinc.

• Jewellers measure the proportion of gold in the alloy in carats. 24 carat being 100% (pure gold), and 18 carat being 75% gold.

• Iron is a much cheaper metal but can be made into a huge variety of steels alloys that contain specific amounts of carbon and other metals to suit a particular purpose. High carbon steel is strong but brittle whereas low carbon steel is softer and more easily shaped.

• More specialised steels containing chromium and nickel (two more transition metals) make stainless steels are hard and resistant to corrosion from air and water.

• Non-transition metal aluminium's alloys are low density and their lightness and strength makes them a good material to use used in the aerospace manufacturing industry.

• Transition metals are good conductors of heat and electricity and can be bent or hammered into shape (malleable), readily drawn into wire (ductile), quite strong physically – made stronger when alloyed with other materials.

• This makes transition metals are useful as structural materials and for making things that must allow heat or electricity to pass through them easily and useful construction materials.

• Pure copper, gold, iron (transition metals) and lead and aluminium (non–transition metals) are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use.
• Transition metals are extremely useful metals on account of their physical or chemical properties eg lack of corrosion and greater strength compared to the Group 1 Alkali Metals.
• An alloy is a mixture of a metal with other elements (metals or non–metals). transition metals can be mixed together to make alloys to improve the metal's properties to better suit a particular purpose. A transition metal alloy mixture often has superior desired properties compared to a pure transition metal i.e. the alloy has its own unique properties and a more useful metal.
• Many transition metals are used in alloys, with a wide range of applications and uses.
  • An ALLOY is mixture of metal with at least one other metallic or non–metallic substances – usually other elements.
  • By mixing metal with metal (and sometimes non–metals) together to make alloys you can improve the metal's properties to better suit a particular purpose.
  • Quite often the presence of different atoms stops the layers of the metal sliding over each other when stressed so making the metal tougher (see Metal Structure for more details about metal properties and alloy behaviour under stress).
  • The point about using alloys is that you can make up, and try out, all sorts of different compositions until you find the one that best suits the required purpose in terms of tensile/compression strength, malleability, electrical conductivity or corrosion resistance etc.
• For catalysts – see above. Their strength and hardness makes them very useful as structural materials.

IRON, Fe

• Iron is a good conductor of heat and can be bent or hammered into shape (malleable), quite strong physically – made stronger when alloyed with other materials.

• This makes iron useful as structural material and for making things that must allow heat to pass through easily and useful construction materials.

• Why make the alloy steel?

  • Most metals in everyday use are alloys.

    • The theory of alloys is explained in the metallic bonding notes.

    • Steel alloys of varying strength and anti–corrosion properties are used in thousands of products and constructions e.g. reinforcing rods in concrete buildings, bridge girders, car engines, domestic appliances from washing machines to electric kettles, saucepans, tools like chisels, ship hulls and superstructure, very hard drill bits,

  • Steel is an alloy because it is a mixture of a metal (iron) with other elements (carbon and perhaps other metals too).

  • Iron from the blast furnace contains about ~96% iron with ~4% of impurities including carbon, silica and phosphorus.

  • In this state the cast iron is too hard and too brittle for most purposes.

  • Cast iron is hard and can be used directly for some purposes eg manhole covers, railings because of its strength in compression and is hard wearing.

  • However, if all the impurities are removed, the resulting very pure iron is too soft for any useful purpose.

  • Therefore, strong useful steel is made by controlling the amount of carbon and selected metals to produce an alloy mixture with the right physical properties fit for a particular application e.g. steel for car bodies, chrome stainless steel, extremely hard and tough tungsten–iron steel alloys etc.

  • The real importance of alloys is that they can be designed to have properties for specific uses.

  • eg low–carbon steels are easily shaped for car bodies, high–carbon steels are hard, and stainless steels are resistant to corrosion etc.

  • Versatile steel is used in building and bridge construction, car bodies, railway lines and countless other objects that need to have a high tensile strength.
  • Cooking pans made of stainless steel are good conductors of heat, strong with good anti–corrosion properties and steel has a high melting point!
  • Compared to iron itself, stainless steel cutlery is stronger AND will not corrode easily in contact with food fluids and washing up water!
• When alloyed with 0.01 to 0.3% carbon iron forms mild steel which is not brittle, but is more malleable and corrosion resistant than cast iron. Mild steel is used for food cans, car bodies (but galvanising and several coats of paint help it to last!) and machinery etc.
• Steel is an alloy based on iron mixed with carbon and usually other metals added too. There are huge number of steel 'recipes' which can be made to suit particular purposes by changing the % carbon and adding other metals e.g. titanium steel for armour plating.

  • Low–carbon steels (0.01 to 0.3% carbon) are easily shaped for car bodies

  • High–carbon steels (0.3 to 2.5% carbon, often with other metals too) are hard wearing and inflexible (but more brittle than low carbon steels) and can be used for cutting tool blades, bridge construction.

  • Stainless steels have chromium (and maybe nickel) added and are rust–resistant to corrosion (from contact with  oxygen & water) than iron or plain steel which readily rust. Stainless steel is corrosion-resistant and hard wearing and is used where the steel is exposed to water and air e.g. for cutlery and 'chrome' parts of road vehicles.

  • Objects made of iron or plain steel, particularly those exposed to the weather, regularly have to be painted or coated with some other protective layer from the effects of water and oxygen.

• Remember! If iron or steel becomes badly corroded, there is no strength in rust!, and, the thicker the rust layer, the thinner and weaker the supporting iron or steel layer, hence the possibility of structural failure.

  • Therefore, most iron and steel structures exposed to the outside weather are maintained with a good coating of paint which may be regularly replaced.

  • Most metals and their alloys will corrode over time, some fast like cast iron, some moderately like copper, others very slow like titanium or aluminium, stainless steel.

  • For chemical details of rusting and its prevention see notes on Corrosion of Metals and Rust Prevention.

• TITANIUM is a strong metal that has a low density and a high resistance to corrosion which makes a good structural material.

• Titanium alloys are amongst the strongest lightest of metal alloys and used in aircraft production.

• As well as its use in aeroplanes it is an important component in nuclear reactor alloys and for replacement hip joints because of its light and strong nature AND doesn't corrode easily.

• Titanium alloys are superior to aluminium alloys, but titanium alloys are more expensive.

• It is one of the main components of Nitinol 'smart' alloys. Nitinol belongs to a group of shape memory alloys (SMA) which can 'remember their original shape'. For example they can regain there original shape on heating (e.g. used in thermostats in cookers , coffer makers etc.) or after release of a physical stress (e.g. used in 'bendable' eyeglass frames, very handy if you tread on them!). The other main metal used in these very useful intermetallic compounds is nickel.

  • Nitinol is an acronym for 'Nickel Titanium Naval Ordinance Laboratory' betraying, like so many technological developments, its military origins, but now acquiring many 'peaceful' uses.

COPPER, Cu

• Copper has properties that make it useful for electrical wiring and plumbing.
  • Copper is a good conductor of electricity and heat, can be bent but is hard enough to be used to make water pipes or tanks and does not readily react with water - good anti-corrosion properties.
• The alloy BRASS is a mixture copper and zinc.
  • It is a much more hard wearing metal than copper (too soft) and zinc (too brittle) and is more malleable than bronze for 'stamping' or 'cutting' it into shape.
  • There is less friction involved in shaping brass so its easily bent and works easier than bronze when used in valves or taps.
  • Brass is used to make fixtures and fittings like door knobs, water taps, screws, hinges, springs and musical instruments like trumpets, trombones, French horns.
  • Bronze is an alloy of copper and tin, harder than brass and is used to make sculptures, medals, ornaments.
• Copper is used in electrical wiring because it is a good conductor of electricity but for safety it is insulated by using poorly electrical conductors like PVC plastic.
  • Like other transition metals, copper is malleable and ductile, easily drawn out into wire, and, more so than most other metals, copper is an excellent conductor of electricity, which is why it is widely used in electrical circuitry.
• Copper is used in domestic hot water pipes because it is relatively unreactive to water and therefore doesn't corrode easily.
  • It is very malleable and copper piping readily bent, so widely used in plumbing.
  • Also, copper being an excellent heat conductor, is useful in heat exchange systems including the immersion cylinder of domestic central heating systems.
  • More on METAL CORROSION
• Copper is used for cooking pans because it is relatively unreactive to water and therefore doesn't corrode easily, readily beaten or pressed into shape but strong enough, it is high melting and a good conductor of heat.
• Copper is also used as a roof covering and weathers to a green colour as a surface coating of a basic carbonate (a green compound) is formed on corrosion.
• The alloy BRONZE is a mixture of copper (Cu) and tin (Sn) and is harder and stronger than copper or tin (both easily bent metals) and just as corrosion resistant. Bronze is used to make springs, motor bearings, bells and sculptures.
• The alloy cupronickel is made by mixing copper and nickel and is a hard wearing metal used in 'silver' coinage.
• Iron and steel are used for boilers because of their good heat conduction properties and high melting point.
• Copper compounds are used in fungicides and pesticides e.g. a traditional recipe is copper sulfate solution plus lime is used to kill greenfly.
• Copper is alloyed with nickel to give 'cupro–nickel', an attractive hard wearing 'silvery' metal for coins.

• Steel, iron or copper are used for cooking pans because they are malleable, good heat conductors and high melting.

• NICKEL is alloyed with copper to give 'cupro–nickel', an attractive hard wearing 'silvery' metal for coins.
• NICHROME is an alloy of chromium and nickel. It has a high melting point and a high electrical resistance and so it is used for electrical heating element wires.
• NITINIOL: Titanium and nickel are the main components of Nitinol 'smart' alloys which are very useful intermetallic compounds. Nitinol belongs to a group of shape memory alloys (SMA) which can 'remember their original shape'. For example they can regain there original shape on heating (e.g. used in thermostats in cookers , coffer makers etc.) or after release of a physical stress (e.g. used in 'bendable' eyeglass frames, very handy if you tread on them!).
  • For more details and examples see SHAPE MEMORY ALLOYS & MAGNETIC SHAPE MEMORY ALLOYS

ZINC

• Zinc is used to galvanise (coat) iron or steel to sacrificially protect them from corrosion. The zinc layer can be put on the iron/steel object by chemical (see electroplating and below) or physically dipping it into a bath of molten zinc.
  • Zinc sulfate solution can be used as the electrolyte for electroplating/galvanising objects with a zinc layer.
  • Zinc is used as a sacrificed electrode in a zinc–carbon battery. It slowly reacts with a weakly acidic ammonium chloride paste, converting chemical energy into electrical energy.
  • The alloy BRASS is a mixture copper and zinc. It is a much more hard wearing metal than copper (too soft) and zinc (too brittle) but is more malleable than bronze for 'stamping' or 'cutting' it into shape.

GOLD

• Gold is also a transition metal and used in jewellery because it doesn't corrode and relatively rare - expensive and conveys high status in many societies.
  • However, pure gold is much too soft and readily wears away.
  • Metals are added e.g. zinc, copper, nickel, palladium and silver are used to make harder wearing gold alloys.
  • Gold has the advantage of never corroding (always nice and shiny), readily shaped and used to make attractive (and costly!) jewellery.
  • Gold alloys are used in dentistry for tooth fillings (you wouldn't want the rotten tooth replaced by one that also corrodes!).
  • Gold is also used in electrical circuits, excellent conductor of electricity and does NOT corrode.
  • Gold has the greatest resistance to corrosion of any element and probably most (if not all?) alloys, so even after thousands of years, archaeologists keep on finding gold objects in good condition!
  • Gold and carat ratings – a measure of gold's purity. Pure gold is described as 24 carat.
    • If gold is described as 16 carat, it means 16 parts of the metal is gold and 8 parts are other metals
    • i.e. 16 carat means 16/24ths gold i.e. 66.7% gold.
  • More on METAL CORROSION

• Paint pigments: chromium oxide Cr₂O₃ green, iron oxide (haematite) Fe₂O₃ red–brown, manganese oxide MnO₂ black, copper hydroxide–carbonates (malachite–green, azurite–blue) and titanium dioxide TiO₂ white.
• Stained glass pigments: cobalt oxide CoO blue, iron oxide/carbonate green, Cu metal red, CuO turquoise.
• TUNGSTEN is used as the filament in light bulbs because its melting point is so high.
• Transition metals like platinum and rhodium are used as metal catalysts in the catalytic converters used in car vehicle exhausts to reduce carbon monoxide and nitrogen oxide polluting emissions.
• Bright, shiny and relatively unreactive copper, silver and gold are used in jewellery - good anti-corrosion properties.
• There is a note about the bonding in metals and structure of alloys on another page.

• Metals can become weakened when repeatedly stressed and strained leading to changes in the crystal structure of the metal and it becomes more brittle. These faults developing in the metal structure is called 'metal fatigue' or 'stress fractures'. If the metal fatigue is significant it can lead to the collapse of a metal structure. So it is important develop alloys which are well designed, well tested and will last the expected lifetime of the structure whether it be part of an aircraft (eg titanium aircraft frame) or a part of a bridge (eg steel suspension cables).

• ALUMINIUM is NOT a transition metal, but is a very useful metal !
  • e.g. it does not form coloured compounds, it does not act as a catalyst etc.
  • BUT it is high melting, of low density and one of the most used and useful non–transition metals.
  • Aluminium is rather weak BUT when alloyed with copper, manganese and magnesium and  it forms a much stronger alloy called duralumin.

  • Magnalium alloys have small amounts of magnesium (~ 5% Mg, ~95% Al) giving the aluminium greater strength, greater corrosion resistance, and lower density than pure aluminium. Therefore these are lighter stronger material and are more malleable and easier to weld than pure aluminium.

    • These tougher aluminium alloys are used in aircraft construction and parts for automobiles.

  • It does not readily corrode due to a permanent Al₂O₃ aluminium oxide layer that rapidly forms on the surface and does not flake off like rust does from iron, and so protects the aluminium from further oxidation.
  • More on METAL CORROSION
  • Because the strength, low density and anti–corrosion properties, aluminium alloys are used in aircraft frame construction and other fittings, window and greenhouse frames, hifi chassis etc.
    • Titanium alloys have superior properties BUT they are more expensive.
  • Its a good conductor of heat and can be used in radiators.
  • Its quite a good conductor of electricity, and also because its light, it is used in conjunction with copper (excellent electrical conductor) in overhead power lines (don't want them too heavy when iced up!).
    • The cables however do have a steel core for strength!
    • Poorly electrical conducting ceramic materials are used to insulate the wires from the pylons and the ground.

  • Steel or aluminium for making car bodies?

    • Aluminium is much more costly to produce than steel.

    • BUT aluminium is less dense (lighter) than steel and saves on fuel and therefore the car economy.

    • ALSO, aluminium car bodies will not corrode like steel and will therefore last longer.

    • Overall it appears at the present time that steel car bodies are used more than aluminium ones.

  • A ~50% mixture of aluminium and magnesium alloy as fine powder, is used in fireworks and burns brightly to give white flashes, just like pure magnesium, but chemically more stable.

More on iron and steel and examples of how metals can be made more useful

• The properties of iron can be altered by adding small quantities of other metals or carbon to make steel.

• Steels are alloys since they are mixtures of iron with other metals or with non–metals like carbon or silicon.

• Making Steel:

  • (1) Molten iron from the blast furnace iron extraction process is mixed with recycled scrap iron

  • (2) Then pure oxygen is passed into the mixture and the non–metal impurities such as silicon or phosphorus are then converted into acidic oxides (oxidation process) ..

    • e.g. Si + O₂ ==> SiO₂   and    4P + 5O₂ ==> P₄O₁₀

  • (3) Calcium carbonate (a base) is then added to remove the acidic oxide impurities (in an acid–base reaction). The salts produced by this reaction form a slag which can be tapped off separately.

    • e.g. CaCO₃ + SiO₂ ==> CaSiO₃ + CO₂ (calcium silicate slag)

  • Reactions (1)–(3) produce pure iron.

  • Calculated quantities of carbon and/or other metallic elements such as titanium, manganese or chromium are then added to make a wide range of steels with particular properties for specific purposes i.e. match the properties of the steel alloy to its use.

  • Because of the high temperatures the mixture is stirred by bubbling in unreactive argon gas!

  • Economics of recycling scrap steel or iron: Most steel consists of >25% recycled iron/steel and you do have the 'scrap' collection costs and problems with varying steel composition* BUT you save enormously because there is no mining cost, no overseas transport costs, no extraction needed, AND less junk lying around! (NOTE: * some companies send their own scrap to be mixed with the next batch of 'specialised' steel they order, this saves both companies money!)

    • All in all, recycling iron/steel, is good 'green' economics, less energy, less pollution, iron ore reserves go further,

• Different steels for different uses:

  • High % carbon steel (0.3 to 2.5% C) is very strong but brittle. It can be used for blades of cutting tools and bridges.

    • You need to watch the blade on a cutting tool doesn't hit an equally hard object e.g. I've broken a lawn mower blade on a stone!

  • Low carbon steel (0.1-0.3% carbon), mild steel is softer and is easily shaped and pressed e.g. into a motor car body.

  • Stainless steel alloys contain chromium and nickel and are tougher and more resistant to corrosion.

  • Very strong steels can be made by alloying the iron with titanium or manganese metal.

• There is a note about the bonding and structure of alloys on another page.

• However, apart from expensive stainless steels using chromium and nickel mixed with iron, most steel alloys readily rusting leading to potential structural weakness and failure or the extra costs involved in protecting the steel.

Two sculptures made of COR-TEN steel: The Anthony Gormley sculpture "The Angel of the North" near Gateshead, North East England.	One of three "Generation" metal sculptures by Joseph Hillier", Newcastle University
The 'artistic' use of weathered steel. The varied chemical composition of Weathering steel grades (%, besides iron) Element C Si Mn P S Cr Cu V Ni Percentage 0.12-0.16 0.25–0.75 0.20–1.25 0.01–0.20 0.030 0.40–1.25 0.25–0.55 0.0-0.10 0.4-0.65 Weathering steel, trademark COR-TEN steel are a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years exposure to weather. As you can see, it is quite a complicated mixture, but still a steel and an excellent application of chemistry to the world of art.

• Steel can be galvanised by coating in zinc, this is physically done by dipping the object into a bath of molten zinc. On removal and cooling a thin layer of zinc is left on. The zinc chemically bonds to the iron via the free electrons of both metals – its all the same atoms to them! It can also be done by electroplating (details below).

• Steel (and most metals) can be electroplated.

  • The steel object to be plated is made the negative electrode (cathode) and placed in a solution containing ions of the plating metal.

  • The positive electrode (anode) is made of the pure plating metal (which dissolves and forms the fresh deposit on the negative electrode).

  • Nickel, zinc, copper, silver and gold are examples of plating metals.

  • The details of copper purification amount to copper plating, so all you have to do is swap the pure negative copper cathode with the metal you want to coat (e.g. Ni, Ag or Au or any material with a conducting surface). Swap the impure positive copper anode with a pure block of the metal you want to form the coating layer. The electrodes dip into a salt solution of nickel, zinc, copper, silver or gold ions etc. and a low d.c. voltage passed through. If M = Ni, Cu, Zn ....

    • At the positive (+) anode, the process is an oxidation, electron loss, as the metal atoms dissolve to form metal(II) ions.

    • M_(s) ==> M²⁺_(aq) + 2e^–

    • at the negative (–) cathode, the process is a reduction, two electron gain by the attracted metal(II) ions to form neutral metal atoms on the surface of the metal being coated.

    • M²⁺_(aq) + 2e^– ==> M_(s)

    • For silver plating it is Ag⁺, Ag and a single electron change.

    • Any conducting (usually metal) object can be electroplated with copper or silver for aesthetic reasons or steel with zinc or chromium as anti–corrosion protective layer.

• Many other metals have countless uses e.g. zinc

  • Zinc is used to make the outer casing of zinc–carbon–weak acid batteries.

  • Zinc is alloyed with copper to make the useful metal brass (electrical plug pins). Brass alloy is stronger and more hardwearing than copper AND not as brittle as zinc.

• Titanium is a transition metal and is strong and resistant to corrosion.

  • Titanium alloys are amongst the strongest and lightest of metal alloys.

  • There is a note about the bonding and structure of alloys on another page.

  • It is used in aeroplanes, in nuclear reactor alloys and for replacement hip joints.

  • It is one of the main components of Nitinol 'smart' alloys. Nitinol belongs to a group of shape memory alloys (SMA) which can 'remember their original shape'. For example they can regain there original shape on heating (e.g. used in thermostats in cookers , coffer makers etc.) or after release of a physical stress (e.g. used in 'bendable' eyeglass frames, very handy if you tread on them!). The other main metal used in these very useful intermetallic compounds is nickel.

    • Nitinol is an acronym for 'Nickel Titanium Naval Ordinance Laboratory' betraying, like so many technological developments, its military origins, but now acquiring many 'peaceful' uses.

• Titanium is extracted from the raw material is the ore rutile which contains titanium dioxide.

• The rutile titanium oxide ore is heated with carbon and chlorine to make titanium chloride

  • TiO₂ + 2Cl₂ + C ==> TiCl₄ + CO₂

• After the oxide is converted into titanium chloride TiCl₄, it is then reacted with sodium or magnesium to form titanium metal and sodium chloride or magnesium chloride. This is an expensive process because sodium or magnesium are manufactured by the costly process of  electrolysis (electricity is the most costly form of energy).

  • This reaction is carried out in an atmosphere of inert argon gas so none of the metals involved becomes oxidised by atmospheric oxygen.

  • TiCl₄ + 2Mg ==> Ti + 2MgCl₂     or    TiCl₄ + 4Na ==> Ti + 4NaCl

  • These are examples of metal displacement reactions e.g. the less reactive titanium is displaced by the more reactive sodium or magnesium.

  • Overall the titanium oxide ore is reduced to titanium metal (overall O loss, oxide => metal)

• Although most metals are relatively good conductors of electricity, all metals do offer electrical resistance.

• When the electric current of electrons meets some resistance in a material, the material heats up and so electrical energy is lost as heat.

• This electrical resistance in metals increases with temperature, so as the wire heats up, even more energy is lost.

• This wasted energy can be minimised if you can operate the circuit at a lower temperature, but not always practicable.

• If you cool a metal down to a sufficiently low temperature, all electrical resistance disappears!

• This is called superconductivity and the metal has become a superconductor.

• If there is no electrical resistance, there is no loss of electrical energy as heat, i.e. energy transfer is 100% efficient.

  • Theoretically in a super–cooled circuit, if you could start a current flowing, it would flow forever, unless you drain some electrical energy off to do some work.

• 

• Transition metals, in the middle of the periodic table (see above) are being used to develop superconducting alloys.

• The potential use of superconductors is enormous e.g.

  • Power cables lose lots of energy, so zero energy loss transmission along power lines would be great.

  • Electrical circuits e.g. in computers, would work faster.

  • The power of electromagnets would be increased with zero resistance flow of electricity through the coils of the magnets.

• Unfortunately there some big technological problems inhibiting the use of superconductors.

  • The main problem is obtaining the really low operating temperature required for superconductivity.

  • In the first experiments, temperatures as low as –265^oC were required.

  • But, using transition metal alloys or oxides and some ceramic materials based on transitional metal compounds it is possible to get the operating temperature up to as high as –130^oC !!!

  • To get these low temperatures requires energy, which is what you are trying to save!

  • In most 'commercial' systems many it is both uneconomic and impractical to operate electrical systems at these very low temperatures to superconduct.

  • Until superconductors are developed that can work at room temperature, only very expensive specialised researched projects can afford to use them.

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Advanced A Level Chemistry Notes on the 3d block & Transition Metals

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