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Advanced Level Inorganic Chemistry Periodic Table Revision Notes

Part 8. The p-block elements: 8.4 Group 6/16 oxygen and sulfur in particular

The physical and chemical properties of the group 6/16 elements, in particular, oxygen and sulphur are described and explained in detail. Data table, symbol equations, oxidation states, formulae of oxides & chlorides etc.

For non-A level students  ...

 (c) doc b KS4 Science GCSE/IGCSE Periodic Table notes links

INORGANIC Part 8 The p-block elements page sub-index: 8.1 Group 3/13 Introduction - Boron & Aluminium * 8.2 Group 4/14 Introduction - Carbon & Silicon - semi-metals e.g Ge * 8.3 Group 5/15 Introduction - Nitrogen & Phosphorus * 8.4 Group 6/16 Introduction - Oxygen & Sulfur * 8.5 Group 0/18 The Noble Gases * 9. Group 7/17 The Halogens (separate section pages)

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots

 

Group 6/16 Introduction

 

Pd s block d blocks and f blocks of metallic elements p block elements
Gp1 Gp2 Gp3/13 Gp4/14 Gp5/15 Gp6/16 Gp7/17 Gp0/18
1

1H

2He
2 3Li 4Be The modern Periodic Table of Elements

ZSymbol, z = atomic or proton number

highlighting position of Group 6/16 elements

5B 6C 7N 8O

oxygen

9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S

sulfur

17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se

selenium

35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te

tellurium

53I 54Xe
6 55Cs 56Ba 57-71 72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po

polonium

85At 86Rn
7 87Fr 88Ra 89-103 104Rf 105Db 106Sg 107Bh 108Hs 109Mt 110Ds 111Rg 112Cn 113Uut 114Fl 115Uup 116Lv

livermorium

117Uus 118Uuo

 

down group 6/16 ===>
property\Zsymbol, name 8O Oxygen 16S Sulphur 34Se Selenium 52Te Tellurium 84Po Polonium (radioactive)
Period 2 3 4 5 6
Appearance (RTP) colourless gas yellow solid (monoclinic/rhombic allotropes) silver metalloid or non-metallic red powder allotropes silver white metalloid radioactive silvery solid
melting pt./oC -218 117 217 450 254
boiling pt./oC -183 445 685 990 962
density/gcm-3 <0.1 2.1 4.8 6.2 9.3
1st IE/ kJmol-1 1314 1000 941 869 812
atomic covalent or metallic radius/pm 73 (cov) 102 (cov) 117 (cov), 190 (met) 135 (cov), 210 (met) 167 (met)
X2- ion radius/pm 140 184 198 221 230
electronegativity 3.44 2.58 2.55 2.10 2.00
simple electron config. 2,6 2,8,6 2,8,8,6 2,8,18,18,6 2,8,18,32,18,6
electron configuration [He]2s22p4 [Ne]3s23p4 [Ar]3d104s24p4 [Kr]4d105s25p4 [Xe]4f145d106s26p4
principal oxidation states -2, +1, (+2) -2, +2, +4, +6 -2, +2, +4, +6 -2, +2, +4, +6 -2, +2, +4, +6
property\Zsymbol, name 8O Oxygen 16S Sulphur 34Se Selenium 52Te Tellurium 84Po Polonium

 

Pd s block d blocks and f blocks of metallic elements p block elements
Gp1 Gp2 Gp3/13 Gp4/14 Gp5/15 Group 6/16 Gp7/17 Gp0/18
1

1H 1s1

2He 1s2
2 3Li [He]2s1 4Be [He]2s2 Electronic structure of selected elements of the periodic table

ZSymbol, Z = atomic/proton number = total electrons in neutral atom

elec. config. abbreviations: [He] = 1s2 [Ne] = 1s22s22p6

[Ar] = 1s22s22p63s23p6     [Kr] = 1s22s22p63s23p63d104s24p6

5B [He]2s22p1 6C [He]2s22p2 7N [He]2s22p3 8O

[He]2s22p4

9F [He]2s22p5 10Ne [He]2s22p6
3 11Na [Ne]3s1 12Mg [Ne]3s2 13Al [Ne]3s23p1 14Si [Ne]3s23p2 15P [Ne]3s23p3 16S

[Ne]3s23p4

17Cl [Ne]3s23p5 18Ar [Ne]3s23p6
4 19K [Ar]4s1 20Ca [Ar]4s2 21Sc [Ar] 3d14s2 22Ti [Ar] 3d24s2 23V [Ar] 3d34s2 24Cr [Ar] 3d54s1 25Mn [Ar] 3d54s2 26Fe [Ar] 3d64s2 27Co [Ar] 3d74s2 28Ni [Ar] 3d84s2 29Cu [Ar] 3d104s1 30Zn [Ar] 3d104s2 31Ga [Ar] 3d104s24p1 32Ge [Ar] 3d104s24p2 33As [Ar] 3d104s24p3 34Se

[Ar] 3d104s24p4

35Br [Ar] 3d104s24p5 36Kr [Ar] 3d104s24p6
5 37Rb [Kr]5s1 38Sr [Kr]5s2 39Y [Kr] 4d15s2 40Zr [Kr] 4d25s2 41Nb [Kr] 4d45s1 42Mo [Kr] 4d55s1 43Tc [Kr] 4d55s2 44Ru [Kr] 4d75s1 45Rh [Kr] 4d85s1 46Pd [Kr] 4d10 47Ag [Kr] 4d105s1 48Cd [Kr] 4d105s2 49In [Kr] 4d105s25p1 50Sn [Kr] 4d105s25p2 51Sb [Kr] 4d105s25p3 52Te

[Kr] 4d105s25p4

53I [Kr] 4d105s25p5 54Xe [Kr] 4d105s25p6
6 55Cs [Xe]6s1 56Ba [Xe]6s2 4f–block and 5d–block in period 6 including Lanthanide Series 81Tl [Xe] 4f145d106s26p1 82Pb [Xe] 4f145d106s26p2 83Bi [Xe] 4f145d106s26p3 84Po

[Xe] 4f145d106s26p4

85At [Xe] 4f145d106s26p5 86Rn [Xe] 4f145d106s26p6
7 87Fr [Rn]7s1 88Ra [Rn]7s2 5f–block & 6d–block including Actinide Series of Metals in period 7 113Uut [Rn] 5f146d107s27p1 114Fl [Rn] 5f146d107s27p2 115Uup [Rn] 5f146d107s27p3 116Lv

[Rn] 5f146d107s27p4

117Uus [Rn] 5f146d107s27p5 118Uuo [Rn] 5f146d107s27p6
  **************************  

 

  • Generally speaking down a p block group the element becomes more metallic in chemical character.

  • Oxygen and sulphur are non-metals, selenium and tellurium are semi-metals, polonium is essentially a metal


OXYGEN - brief summary of a few points

  • The structure of the element:

    • Non-metal existing as diatomic molecule, O2, with a double covalent bond.

    • It has two allotropes: 'normal oxygen' O2 (dioxygen above) and the highly unstable and reactive gas ozone, O3 (trioxygen).

  • Physical properties of the element

    • O2 is a colourless gas; mpt -218oC; bpt -183oC;  poor conductor of heat/electricity.

      • O3 is a pale blue gas.

  • Group, electron configuration (and oxidation states)

    • Gp6; e.c. 2,6  or 1s22s22p4;  Normally (-2) e.g. H2O, CO2 etc. but can have other oxidation states ...

    • e.g. H2O2 (-1), F2O (+2).

  • Reaction of element with oxygen

    • O2 molecules won't react with themselves BUT in the upper atmosphere oxygen atoms are formed by high energy radiation/particle collision with oxygen molecules causing homolytic bond fission to produce free oxygen atom (free radicals). These combine with oxygen molecules to form ozone. Ozone can be synthesised by an electric discharge through oxygen.

      • (i) O2 = hv => 2O. (ii) O. + O2 ==> O3 

  • Reaction of oxide with water, acids or bases/alkalis: Not applicable.

  • Reaction of element with chlorine

    • None, but unstable chlorine(I) oxide (chlorine monoxide) can be made indirectly and there are other chlorine oxides. (see chlorine)

  • Reaction of chloride with water:

    • Slowly hydrolyses to form weak chloric(I) acid.

      • Cl2O(g) + H2O(l) ==> 2HClO(aq)

  • Reaction of element with water:

    • Slightly soluble but no reaction.

  • Other comments:

    • Formed in plant photosynthesis. Consumed in respiration.

  • Links to other pages on site


SULFUR/SULPHUR - brief summary of a few points

  • The structure of the element:

    • Three solid allotropes. Two are crystalline lattices based on S8 molecules (rhombic and monoclinic sulfur). A 3rd form is an unstable dark brown-black polymeric form called plastic sulphur, formed when boiling sulphur is poured onto cold water, great fun, but of little use!

  • Physical properties

    • Colourless gas; mpt 117oC; bpt 445oC; poor conductor of heat/electricity.

  • Group, electron configuration (and oxidation states)

    • Gp6; e.c. 2,6  or 1s22s22p63s23p4; ranges from (-2 to +6) e.g.

    • Na2S (-2), S2Cl2 (+1), SO2 (+4) and H2SO4, SF6, SO3 (all +6).

  • Reaction of element with oxygen

    • Burns in air with a pale blue flame to form sulphur dioxide (sulphur(IV) oxide), with a little sulphur trioxide.

      • S(s) + O2(g) ==> SO2(g) 

    • Sulphur trioxide (sulphur(VI) oxide) has to be made by the industrial Contact Process.

      • 2SO2(g) + O2(g) == V2O5 catalyst, 450oC ==> 2SO3(g) 

  • Reaction of the oxides with water: Both dissolve to form acid solutions.

    • Sulphur dioxide forms the weak 'fictitious' sulphurous acid.

      • SO2(g) + H2O(l) ==> H2SO3(aq) 

        • the reaction is better represented ionically as ..

        • SO2(aq) + H2O(l) H+(aq) + HSO3-(aq) 

    • Sulphur trioxide reacts very violently and exothermically to form the oily liquid, strong sulphuric acid.

      • SO3(g) + H2O(l) ==> H2SO4(l) 

      • In water, the sulphuric acid is almost fully ionised.

        • H2SO4(aq) + 2H2O(l) ==> 2H3O+(aq) + SO42-(aq) 

  • Reaction of oxide with acids:

    • None, only acidic in nature.

  • Reaction of oxide with bases/alkalis:

    • Sulphur dioxide dissolves in strong bases to form sulphites/sulphate(IV)s

    • 2NaOH(aq) + SO2(g) ==> Na2SO3(aq) + H2O(l) formation of sodium sulphite/sulphate(IV)

    • ionic equation: 2OH-(aq) + SO2(g) ==> SO32-(aq) + H2O(l)

    • You would NOT attempt to react sulphur trioxide with water, the reaction is very violent and exothermic.

    • but theoretically: 2NaOH(aq) + SO3(g) ==> Na2SO4(aq) + H2O(l)

  • Reaction of element with chlorine

    • When chlorine is passed over molten sulphur a variety of chlorides are formed.

    • The main product is disulphur dichloride

    • 2S(s) + Cl2(g) ==> S2Cl2(l) (also SiCl2, SiCl4)

  • Reaction of chloride with water:

    • Slowly hydrolyses in water, via a complex reaction, to form an acid solution of several products (not meant to be a balanced equation).

      • S2Cl2(g) + H2O(l) ==> HCl(aq), S(s), SO2(aq), H2SO3(aq),  H2SO4(aq), H2S(aq)

        • a rather complex redox/hydrolysis reaction! 

  • Reaction of element with water:

    • None.


 

 Shapes and bond angles of molecules and ions of oxygen and sulfur

 

(c) doc boxygen molecule O2

(c) doc b(c) doc b(c) doc belectrons: two bond pairs and two lone pairs, ANGULAR or BENT shape: e.g. hydrogen sulphide, H2S, or water H2O, i.e. H2X with H-X-H bond angle of approximately 109o and similarly ions like NH2-. Note: the exact H-O-H angle is 104.5o due to the extra repulsion of two lone pairs. (Q = H, X = O, S etc. in group 6)

 

(c) doc b(c) doc b

electrons: 6 bond pairs, OCTAHEDRAL SHAPE: e.g. sulfur(VI) fluoride (sulphur hexafluoride molecule) SF6 with Q-X-Q bond angles of 90o and 180o (Q = F, X = S)

 

selected molecule/ion shapes based on sulfur

Sulfur(IV) oxide/sulphur(VI) oxide, SO2 (sulphur dioxide/sulfur dioxide) molecule is a bent shape (angular), O-S-O bond angle ~120o due to two groups of bonding electrons and one non-bonding lone pair of electrons.

The sulfate(IV) ion/sulphate(IV) ion, SO32- (sulfite ion/sulphite ion) is a trigonal pyramid shape, O-S-O bond angle ~109o due to three groups of bonding electrons and one lone pair of electrons.

Sulphur(VI) oxide/sulfur(VI) oxide, SO3 (sulfur trioxide/sulphur trioxide), is a trigonal planar shape, O-S-O bond angle of 120o due to three bonding groups of electrons and no lone pairs of electrons.

Sulfate(VI) ion/sulfate(VI) ion, SO42- (sulphate ion/sulfate ion) is tetrahedral in shape, O-S-O angle of 109.5o. due to four groups of bonding electrons and no lone pairs of electrons.

The shapes are deduced below using dot and cross diagrams and VSEPR theory and illustrated valence bond dot and cross diagrams below.

-


 

Why is sulphuric acid a useful material? How is it made? Contact Process

Because sulfuric acid has so many uses the industrial development of a country is sometimes measured by the amount of sulphuric acid that is used each year. Sulphuric acid is made starting from the element sulphur which is found in the Earth's crust.

  • Sulphuric acid is used as car battery acid and is used to make fertilisers,  dyes and detergents.

    • e.g. ammonia + sulphuric acid ==> ammonium sulphate (a fertiliser salt)

    • 2NH3(aq) + H2SO4(aq) ==> (NH4)2SO4(aq) => evaporation to get crystals

    • Its acid action make it good for cleaning metal surfaces in industry.

  • Sulphuric acid is manufactured from the raw materials sulphur, air and water and involves the production of sulphur trioxide in the Contact Process.

  • (1) Sulfur is burned in air to form sulphur dioxide (exothermic).

    • In the reaction the sulphur is oxidised (O gain)  (1a) S(s) + O2(g) ==> SO2(g)

    • Sulfur dioxide can also be indirectly obtained from the process of extracting copper from copper sulphide ores e.g. in a copper smelter: (1b) Cu2S(s) + O2(g) ==> 2Cu(l) + SO2(g)

  • Note: Sulphur dioxide itself is a useful chemical in its own right:

    • It is used as a bleach in the manufacture of wood pulp for paper manufacture

    • and its toxic nature makes it useful as a food preservative by killing bacteria.

  • (2) The Contact Process of sulphur trioxide production must be economically efficient for the manufacture of the important industrial chemical sulphuric acid.

    • In the Contact Process reactor the sulphur dioxide is mixed with air (the required stoichiometric volume/mole SO2:O2 ratio is 2:1, in practice 1-2:1 is used) and the mixture passed over a catalyst of vanadium(V) oxide V205 at a relatively high temperature of about 450°C and at a pressure of between 1-2 atm.

  • In the reactor the sulphur dioxide is oxidised in the reversible exothermic reaction ...

    •   (2) 2SO2(g) + O2(g) (c) doc b 2SO3(g)

    • Kp =

        pSO32
      -------------------
      pSO22 pO2
  • The reaction forms sulphur trioxide and the equilibrium is very much to the right hand side ...

    • The reaction forms sulphur trioxide and the equilibrium is very much to the right hand side because despite the reaction being exothermic a relatively high temperature is used which favours the reverse reaction R to L, from the energy change equilibrium rule, i.e. increasing temperature shifts the equilibrium in the endothermic direction. However the value of Kp is high enough to give a 99% yield.

    • The reaction is favoured by high pressure (pressure equilibrium rule, 3 => 2 gas molecules, LHS ==> RHS), but only a small increase in pressure is used to give high yields of sulphur trioxide, because the formation of SO3 on the right hand side is so energetically favourable (approx. 99% yield, i.e. only about 1% SO2 unreacted).

    • The use of the V2O5 catalyst ensures a fast reaction without having to use too a higher temperature which would begin to favour the left hand side too much (energy change equilibrium rule), but remember a catalyst does not affect the % yield or equilibrium concentration of SO3, you just get there more economically faster.

    • Multiple reactor beds are used to ensure the maximum % conversion and heat exchange systems are used to control the temperature, and pre-heat incoming reactant gases.

  • (3) The sulphur trioxide is dissolved in concentrated sulphuric acid to form fuming sulphuric acid (oleum).

    • SO3(g) + H2SO4(l) ==> H2S2O7(l)

  • (4) Water is then carefully added to the oleum to produce concentrated sulphuric acid (98%).

    • H2S2O7(l) + H2O(l) ==>  2H2SO4(l)

    • If the sulphur trioxide is added directly to water an acid mist forms which is difficult to contain because the reaction to form sulphuric acid solution is very exothermic!

    • If you 'add' equations (3) + (4) you get

      • (5) SO3(g) + H2O(l) ==>  H2SO4(l)

  • Good anti-pollution measures need to be in place since the sulphur oxides are harmful and would cause local acid rain! To help this situation AND help the economics of the process, any unreacted sulphur dioxide is recycled through the reactor.

  • Concentrated sulphuric acid can be used in the laboratory as a dehydrating agent.

    • Dehydration is the removal of water or the elements of water from a compound and can be described as an elimination reaction. Usually and adjacent H and OH in a molecule are removed to form the water.

    • When added to some organic compounds containing hydrogen and oxygen, e.g. sugar, concentrated sulphuric acid removes the elements of water from the compound leaving a 'spongy' black carbon residue.

    • If alcohols are heated with conc. sulphuric acid, they are dehydrated to alkenes.

      • e.g. ethanol ==> ethene + water

      • CH3CH2OH ==> CH2=CH2 + H2O

    • When added to blue copper sulphate crystals concentrated sulphuric acid removes the water of crystallisation leaving white anhydrous copper sulphate. In this case the water already exists BUT not in a mixture and so the following reaction is classified as a chemical change.

      • CuSO4.5H2O(s) (c) doc b CuSO4(s) + 5H2O(absorbed into the H2SO4 which it reacts with)

    • Conc. H2SO4 catalyses the reaction between an alcohol and carboxylic acid to form an pleasant smelling ester liquid but it isn't considered a dehydration reaction (H comes from one molecule and OH from the other).

      • e.g. the esterification ethanoic acid + ethanol ==> ethyl ethanoate + water

      • CH3COOH + CH3CH2OH ==> CH3COOCH2CH3 + H2O

    • a dreshchel/dreschler bottle (c) doc bConcentrated sulphuric acid can be used as a drying agent e.g. in the preparation of gases.

      • The prepared gas is bubbled through a dreschel/dreschler bottle (illustrated on the right), containing the concentrated sulphuric acid. In this case the water vapour is just a component in a gaseous mixture. Most gases can be dried in this way except the alkaline gas ammonia which will exothermically react to form a solid salt. In this case the water vapour is just a component in a gaseous mixture.

 


 

Analysis of some REDOX reactions

  • The oxidation of sulphur dioxide with bromine

    • SO2(aq) + Br2(aq) + 2H2O(l) ==> SO42-(aq) + 2Br-(aq) + 4H+(aq)

    • (i) the oxidation half reaction is: SO2(aq) + 2H2O(l) ==> SO42-(aq) + 4H+(aq) + 2e-

      • The sulphur changes from ox. state +4 to +6 (SO2 to SO42-).

    • (ii) the reduction half-reaction is: Br2(aq) + 2e- ==> 2Br-(aq)

      • Two bromine atoms (as molecule) change from ox. state 0 to -1.

    • The hydrogen (+1) and oxygen (-2) do not change oxidation state.

      • (i) + (ii) equals the balanced equation, 2 electrons gained and lost or an ox. state rise and fall of 2 units.

      • Bromine is the oxidising agent (gain/accept e-s, lowered ox. state),

      • and sulphur dioxide is the reducing agent (loses e-s, inc. ox. state of S).

    • Sulphur dioxide does ionise to a small extent in water to give the sulphite ion, and adding a strong non-oxidising acid like dilute hydrochloric acid to sodium metabisulphite produces the ion, which means another equation can also adequately describe the redox change in terms of sulphur and bromine.

      • e.g. if the sulphite ion acts as the reducing agent the reaction with chlorine would be written as:

      • SO32-(aq) + Cl2(aq) + H2O(l) ==> SO42-(aq) + 2Cl-(aq) + 2H+(aq)

  • The oxidation of hydrogen sulfide by iron(III) ions

    • If an iron(III) salt (old name, ferric salt) is added to hydrogen sulphide solution a precipitate of sulphur forms and the orange-brown solution turns pale green.

    • H2S(aq) + 2Fe3+(aq) ==> 2Fe2+(aq) + 2H+(aq) + S(s)

    • Oxidation: 1 S at (-2) change to 1 S at (0), H2S ==> S, a loss of 2 electrons, inc. 2 ox. state units.

    • Reduction: 2 Fe at (+3) change to 2 Fe at (+2), gain in total of 2 electrons, decrease in 2 ox. state units.

    • No change in the oxidation state of the 2H's (+1) involved.

    • The iron(III) ion acts as the oxidising agent (gains/accepts e-s, lowered ox. state of Fe) and the hydrogen sulphide is the reducing agent (loses/donates e-s, inc. ox. state of S).

  • The decomposition of hydrogen peroxide

    • Hydrogen peroxide decomposition, catalysed by the black solid manganese(IV) oxide, MnO2.

      • 2H2O2(aq) ==> O2(g) + 2H2O(l)

      • Ox. state changes: 4O at (-1) change to 2O at (0) in O2 and 2O at (-2) in H2O

      • and H is unchanged at (+1).

    • A case of disproportionation where an element in a species simultaneously changes into a higher and lower oxidation state i.e. here two oxygen atoms increase their oxidation state and two oxygen atoms decrease their oxidation state.

    • It also means that hydrogen peroxide simultaneously acts as a reducing agent and oxidising agent.

  • -

 

WHAT NEXT?

INORGANIC Part 8 The p-block elements page sub-index: 8.1 Group 3/13 Introduction - Boron & Aluminium * 8.2 Group 4/14 Introduction - Carbon & Silicon - semi-metals e.g Ge * 8.3 Group 5/15 Introduction - Nitrogen & Phosphorus * 8.4 Group 6/16 Introduction - Oxygen & Sulfur * 8.5 Group 0/18 The Noble Gases * 9. Group 7/17 The Halogens (separate section pages)

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots

 

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