• Index of links for this GCSE/IGCSE TRANSITION METALS page:

  • Where are the Transition Metals Series in the Periodic Table?

  • (a)-(c) Physical properties of transition Metals - strength, melting/boiling points, density

  • (d) Chemical-reactions properties

  • (e) Use as catalysts

  • (f) More on uses of Transition Metals/compounds/alloys

  • (g) Note on uses of other non-transition metals/alloys e.g. aluminium/duralumin (Al is NOT a transition metal)

The basic structure of the Periodic Table and where are the '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 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).
• On Period 4 is a horizontal row of ten elements between Group 2 and Group 3, and from Sc to Zn are called the 1st Transition Metals Series of Elements ...
  • ... bottom-middle of the partial diagram of the Periodic Table above,
  • directly below them, but not shown, are further transition metal series,
  • so the Transition Metals Series are just a horizontal section of a period of the Periodic Table.

(a) Some General Physical Characteristics

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

• Good conductors of heat and electricity (there have many free electrons per atom to carry thermal or electrical energy ).They are easily hammered and bent into shape. They are typically lustrous/shiny solids (or liquids).

(b) High Melting Point and Boiling Point

• 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 compare with Group 1 Alkali Metals).
• Mercury is in another transition metal, but unusually, it has a very low melting point of -39^oC.
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.

(c) 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).

THE CHEMISTRY OF TRANSITION METALS

Their chemical properties and chemical reactions

(d)(i) Form coloured compounds and ions in solution

They tend to be much less reactive than the Alkali Metals. They do not react as quickly with water or oxygen so do not corrode as quickly. Transition metals tend to form more coloured compounds more than 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 coloured ions/compounds often have quite a complex structure and indeed called complexes.

1. Sc - scandium salts, such as the chloride, ScCl_3, are colourless and are not typical of transition metals
2. Ti - titanium(III) chloride, TiCl₃, is purple
3. V - vanadium(III) chloride, VCl₃, is green
4. Cr - chromium(III) sulphate, Cr₂(SO₄)₃, is dark green (chromate(VI) salts are yellow, dichromate(VI) salts are orange)
5. Mn - manganese compound -  potassium manganate(VII), KMnO₄, is purple (manganese(II) salts eg MnCl₂ are 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.
7. Co - cobalt sulphate, CoSO₄, is pinkish
8. Ni - nickel chloride, NiCl₂, is green
9. Cu - copper(II) sulphate, CuSO₄, is blue.
   • 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) sulphate, CuSO₄, from dilute sulphuric 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.
     • 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) sulphate, Cu₂SO₄, a white solid.
10. Zn - zinc salts such as zinc sulphate, ZnSO₄, are usually colourless and are not typical of transition metals.

• 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 hydroxide precipitates when mixed with aqueous sodium hydroxide solution.

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

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

• ionically the precipitation reaction is :

  • metal ion + hydroxide ion ==> hydroxide precipitate

  • M²⁺_(aq) + 2OH^-_(aq) ==> M(OH)_2(s) 

  • M can be for the ...

    • 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

    ,

    • e.g.

    • 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)

  • or for the copper(II) ion Cu²⁺, blue in aqueous solution,

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

    • e.g.

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

      • 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 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.

  • and for the iron(III) ion Fe³⁺:

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

    • e.g.

    • 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)

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

• 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.
• Many 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.
• For catalysts - see above. Their strength and hardness makes them very useful as structural materials.

IRON, Fe

• Cast iron is used for man-hole covers because it is so hard wearing but it is brittle due to a high carbon content.
• When alloyed with 1% 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.

• CHROMIUM, Cr
  • Chromium steel (stainless steel, mixing and melting together Fe + Cr and maybe Ni too) with good anti-corrosion properties, used for cutlery and chemical plant reactors.

COPPER, Cu

• 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.
• 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.
• Copper is used in domestic hot water pipes because it is relatively unreactive to water and therefore doesn't corrode easily.
• 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 is formed on corrosion.
• The alloy BRONZE is a mixture of copper and tin (Sn) and is stronger than copper and just as corrosion resistant, e.g. used for sculptures.
• 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 sulphate 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.

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 sulphate 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.

Transition metal compounds (often oxides) of copper, iron, chromium and cobalt are used to pigments for artwork, and give bright colours to stained glass and ceramic/pottery glazes e.g.

• 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: cobalt oxide CoO blue, iron oxide/carbonate green, Cu metal red, CuO turquoise.

• 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!). The other main metal used in these
• 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.
• There is a note about the bonding in metals and structure of alloys on another page.

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(g) What about the uses of non-transition metals?

Note on Aluminium

• Aluminium is NOT a transition 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.
  • It is rather weak BUT when alloyed with copper, manganese and magnesium and  it forms a much stronger alloy called duralumin.
  • It does not readily corrode due to a permanent Al₂O₃ aluminium oxide layer on the surface which does not flake off and protects the aluminium from further oxidation.
  • Because of its alloyed strength, lightness and anti-corrosion properties it is used in aircraft construction, window frames, hifi chassis etc.
  • 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.

More on aluminium and iron - Examples of how metals be made more useful

• Aluminium is a reactive metal but it is resistant to corrosion. This is because aluminium reacts in air to form a layer of aluminium oxide which then protects the aluminium from further attack.

  • This is why it appears to be less reactive than its position in the reactivity series of metals would predict.

• For some uses of aluminium it is desirable to increase artificially the thickness of the protective oxide layer in a process is called anodising.

  • This involves removing the oxide layer by treating the aluminium sheet with sodium hydroxide solution.

  • The aluminium is then placed in dilute sulphuric acid and is made the positive electrode (anode) used in the electrolysis of the acid.

  • Oxygen forms on the surface of the aluminium and reacts with the aluminium metal to form a thicker protective oxide layer. 

• Aluminium can be alloyed to make 'Duralumin' by adding copper (and smaller amounts of magnesium, silicon and iron), to make a stronger alloy used in aircraft components (low density = 'lighter'!), greenhouse and window frames (good anti-corrosion properties), overhead power lines (quite a good conductor and 'light'), but steel strands are included to make the 'line' stronger and poorly electrical conducting ceramic materials are used to insulate the wires from the pylons and the ground.

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

• 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, or 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.

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

  • Economics of recycling scrap steel or ion: 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 or overseas transport costs 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!)

• Different steels for different uses:

  • High % carbon steel is strong but brittle.

  • Low carbon steel or 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.

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

  • Titanium alloys are amongst the strongest 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)