Doc Brown's Chemistry  Answers to the Periodic Table Worksheet of structured questions

ANSWERS TO SOME OF THE KS4 Science GCSE/IGCSE TASK SHEET of structured QUESTIONS on the Periodic Table

Revision KS4 Science IGCSE/O level/GCSE Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science  (revise courses equal to US grades 9-10)

1. The Historic Development of the Periodic Table

2. The Periodic Table, a basic exercise

3. Group 7 Halogens - properties & uses of elements/compounds

4. The Extraction-purification of Metals - iron, aluminium and copper

1. The Historic Development of the Periodic Table

(original task sheet and the answers should be discussed and thought about in an open-minded way)

Detailed GCSE revision notes on the Periodic Table

• Q1 Based on Antoine Lavoisier's classification of 1789

  • (a) (i) Substance can't be spit into simpler substances, (ii) one or more elements chemically combined to form a new substance.

  • (b) 'light' and 'caloric', not substances at all!

  • (c) Sort of!, mainly the element carbon, but is a mixture, but not bad for 1789?

  • (d) There oxides are soluble in water forming acids eg litmus turns red.

  • (e) Yes all metallic elements, doubt if they were pure though!

  • (f) Basically yes, judging from the first three columns listed, 4th column is a problem!

  • (g) The 'earthy elements', which are compounds, a chemical combination of a metal plus oxygen or sulfur (both in case of barium).

  • (h) He didn't have the high temperature, reactive metal or electrolysis 'knowledge' to 'separate' the elements in some way eg extract a reactive metal. In other words the wrong classification was due to a lack of chemical technical knowledge.

• Q2 Based on the 1829 work of Johann Döbereiner

  • (a) The 'group' idea of chemically very similar elements.

  • (b) (i) Group 1 Alkali Metals, (ii) Group 2 Alkaline Earth Metals, (iii) Group 7 Halogens.

• Q3 Based on the work of John Newlands 1864

  • (a) eg almost completely genuine elements (Di was a mix of two elements), classified roughly into groups of similar elements, 1st real recognition of 'periodicity'

  • (b) Wider range of elements 'quoted' in 'groups', recognised that the 'groups' had more than 3 elements, correct to mix up metals and non-metals in same group eg 5th column.

  • (c) Not precisely BUT be 'fair' to him, half of column 2 is Group 1, half of column 3 is Group 2, half of column 5 is Group 4, half of column 6 is Group 5, half of column 7 is Group 6. (If he had put his column 1 as column 7, quite a lot would match today!

  • (d) None of his vertical column groups match completely but from (c) above, the basic pattern was emerging. However column's 1 and 7 do seem particularly mixed up compared to the modern periodic table.

  • (e) Column 4 has B and Al, column 5 C and Si with Sn, column 6 has N and P with Sb and Bi.

  • (f) The 'Group' and 'Period' (see answer to (a))

• Q4 Based on Dmitri Mendeleev's Periodic Table of 1869

  • (a) In order of 'atomic weight' (we know call relative atomic mass).

  • (b) Group 0 (or 8) The Noble Gases. These were not completely found and characterised until the 1890's.

  • (c) Above Y is Sc, below Al is Ga, below Si is Ge

  • (d) (i) pattern from looking at the properties of the elements above and below 'x'. (ii) and (iii) Sc a metal, Sc₂O₃ and ScCl₃ (like Al), Ga metal Ga₂O₃ and GaCl₃ (like Al), Ge a metal GeO₂, GeCl₄  (like C). (BUT at a 'deeper' level Ga and Ge  are semi-metals with intermediate properties overall).

  • (e) Increased number of known elements, groups becoming more clearly defined (he used a double column approach which is not incorrect, i.e. a sort of group xA and xB classification), order across a period much better, sufficiently accurate to predict missing elements and their properties.

• Q5 Based on a typical modern version of the Periodic Table

  • (a) In order of atomic (proton) number.

  • (b) Due to isotopic masses, the relative atomic mass does go 'down' occasionally (there is no obvious 'nuclear' rule that applies). BUT chemically Te is S and Se etc. and I is like Cl and Br etc. This is now backed up by modern knowledge of electron structure.

  • (c) Most importantly, it is complete bar newly 'man-made' elements (see (d) below). We now know the electronic structure of elements and can understand sub-levels and the 'rules' in electron structure eg 2 in shell 1 (period 1, 2 elements H to He), 8 in shell 2 (period 2, 8 elements Li to Ne), there is a sub-level which allows an extra 10 elements (the transition metals) in period 4 (18 elements, K to Kr). this also explains the sorting out of Mendeleev's A and B double columns in a group (but that's for much more advanced chemistry!). The periods are complete now that we know about Noble Gases.

  • (d) In the 1940's Glenn Seaborg was part of a research team developing the materials required to produce the first atomic bombs dropped on Hiroshima and Nagasaki. He specialised in separating all the substances made in the first nuclear reactors and helped discover the series of 'nuclear synthesised' elements beyond the naturally occurring limit of uranium (₉₂U). From element 93 to 109? are now known, so who knot's next year+ ...? Will the structure of the bottom part of the periodic table grow? change? There is plenty of scope for present day, and future Mendeleev's!!!! (will you be one of them'?).

    • Glen Seaborg was a Nobel Prize winner and is considered one of Americas four greatest chemists from a vote by the American Chemical Society: The others are ...

    • Linus Pauling, who nearly beat Crick and Watson to the structure of DNA and was, prior to his death, still happily, and enthusiastically, writing research papers at 85 from his California beach house overlooking the Pacific, (and I've just retired at 58!). He is one of my real chemical hero's and I've got a 2nd hand copy of his 1950 textbook on "Chemical Bonding" and such a revelation to any serious student (in the 60's), probably looks a bit old-fashioned to a modern student!

    • Wallace Carothers who (prior to committing suicide) synthesised Nylon and Neoprene (1st artificial rubber). He suffered from extreme depression and his immense success seems to have offered little comfort for him after the death of his favourite sister. Sad, but, chemists are just another cross-section of society.

    • Robert Woodward was a fantastic organic chemist both 'practically' and 'theoretically'.

2. The Periodic Table - Basic Exercise (original task sheet)

GCSE revision notes on the Periodic Table * Detailed GCSE revision notes on the Group 1 Alkali Metals

Detailed GCSE revision notes on Group 7 The Halogens * Detailed revision notes on Atomic Structure

• Q1 (a) zig zag line 'roughly goes through B\Al, Al\Si, Ge\As, Sb\Te, Bi\Po

  • (b) 3/4 are metals.

• Q2 (a) METALS: high melting/boiling points (all solid at room temperature except mercury), high density, good conductors of heat/electricity, shiny 'lustrous' surface, strong material.

  • (b) NON-METALS: low melting/boiling points (can be gas, liquid or solid at room temperature), low density, poor conductors of heat/electricity (heat and electrical insulators), dull surface and soft or brittle when solid.

• Q3 (a) METALS: (i) form basic oxides which react with acids to form salts, if oxide soluble in water an alkali is formed and turn litmus blue; (ii) react with acids to form a salt solution and hydrogen gas, (iii) readily combine with non-metals to form ionic compounds

  • (b) NON-METALS: (i) form acidic oxides that react with alkalis to form salts, if oxide soluble in water it will turn litmus red; (ii) do not usually react with acids, (iii) readily combine with metals to form ionic compounds, (iv) combine with other non-metals to form covalent compounds.

• Q4 (a) GROUP - vertical column of chemically similar elements eg Li to Cs are the very reactive Alkali Metals

  • (b) PERIOD - a whole horizontal row of elements of varying character eg metals ==> non-metals from left ==> right

  • (c) TRANSITION METALS - a series of similar metals which form part of a period, they are strong, high melting, act as catalysts, form coloured compounds

• Q5 Li-Cs group 1, Be-Ba group 2, B-Tl group 3, C-Pb group 4, N-Bi group 5, O-Po group 6, F-At group 7, He-Rn group 0 or 8

• Q6 (a) horizontally: period 1 is H to He, period 2 is Li to Ne, period 3 is Na to Ar, period 4 is K to Kr etc.

  • (b) period 1 hydrogen to helium, period 2 lithium to neon, period 3 sodium to argon

• Q7 (a) Group 1 - lithium, sodium, potassium etc., (b) Group 7 - fluorine, chlorine, bromine etc., (c) Group 0 or 8 - helium, neon, argon etc., (d) 1st Transition Metal series - scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc

• Q8 Originally placed in order of 'atomic weight' (we now call this 'relative atomic mass')

• Q9 Now placed in order of atomic (proton) number.

• Q10 Potassium is a very reactive metal and chemically very similar to sodium and rubidium etc. and nothing like the unreactive non-metal Noble Gases like neon and krypton.

  • Argon is an unreactive non-metal very similar to neon and krypton, and bears little similarity with sodium or rubidium.

• Q11 (a) 2 electrons in 1st shell, 8 in 2nd, 8 in 3rd

  • (b) Group number equals the number of electrons in the outer shell

    • except hydrogen doesn't readily into a group and helium can only have two electrons due to the 'rules', but it does have a full outer shell like Ne to Rn.

  • (c) The number of electron shells used equals the period number eg Na is 2.8.1 in period 3

• Q12 (a) B 4 outer electrons, (b) A in group 7, (c) D 4 shells used, (d) D in Group 1 Alkali Metal, (e) A Group 7 Halogen

• Q13 (a) chlorine, halogen in group 7; (b) a transition metal eg chromium, iron, copper, nickel; (c) group 1 alkali metal eg sodium or potassium; (d) a noble gas eg helium or neon, (e) copper, a transition metal (with gold, they are the only two metals which are not shiny silver-grey); (f) group 1 alkali metals like sodium or potassium; (g) bromine in group 7 halogens; (h) argon, an unreactive noble gas.

3. The Group 7 Halogens the properties and uses of the elements and compounds (original task sheet)

Detailed GCSE revision notes on Group 7 The Halogens

• TASK 1: The properties of the Group 7 Halogens

  • Q1 (a) fluorine, 2.7; chlorine, green gas, -102^oC, -34^oC, 2.8.7; bromine, dark red liquid, -7^oC, 59^oC; iodine, dark/black solid, 114^oC, 184^oC

    • (b) gets darker down the group

    • (c) on heating: bromine gives orange-brown vapour, iodine gives a brilliant purple vapour

  • Q2(a) exist as gas, liquid or solid with low melting/boiling points

    • (b) weak when solid, poor conductors of heat and electricity

  • Q3(a) melting/boiling points increase down the group

    • (b) change from gas ==> liquid ==> solid

  • Q4 The exist as X₂ molecules, 2 X atoms per molecule, where X = F, Cl, Br, I or At

  • Q5(a) form ionic compounds with metals

    • (b) Cl^- single minus, because it gains one extra negative electron more than the number of positive protons, to be electronically stable like a noble gas (from Cl [2.8.7] to Cl^- [2.8.8]^-)

  • Q6 With non-metals they form covalent compounds

  • Q7 Chlorine: turns damp blue litmus red before bleaching it white; iodine gives a dark blue-black colour with starch solution

• TASK 2: The reactivity trend of the halogens

  • Q1a Observations of mixing halogen solutions with halide salt solutions.

    halogen\salt	Potassium chloride	Potassium bromide	Potassium iodide	Water blank (fair test check)
    chlorine water (pale green solution)	very pale green solution - no real colour change	orange colour - change!	dark colour and maybe a black precipitate - change!	very pale green solution
    bromine water (orange solution)	pale orange to yellow solution - no real colour change	pale orange to yellow solution - no real colour change	dark colour and maybe a black precipitate - change!	pale orange to yellow solution
    iodine water (very dark solution)	paler dark coloured solution - no real colour change	paler dark coloured solution - no real colour change	no change (but complicated by the formation of the darkly coloured I3- ion)	paler dark coloured solution

  • Q1b The blanks is to see if there is any colour change due to a reaction, other than the colour observed of chlorine, bromine or iodine solution on dilution. If there is a displacement reaction, a 'darker' colour is observed.

  • Q2a Chlorine displaces bromine and iodine. Q2b Bromine displaces iodine. Q2c Iodine does not displace anything here.

  • Q3a A more reactive element will displaces a less reactive element. This rule applies to a series of non-metals like halogens, or a series of metals.

  • Q3b The most reactive will displace the most number of other elements, therefore the reactivity trend for the Group 7 Halogens, from most to least reactive is chlorine > bromine > iodine

  • Q3c The above trend means that Group 7 Halogens get less reactive down the group with increasing atomic number.

  • Q3d Group 0 Noble Gases have full sub-shells of electrons (e.g. 2.8 or 2.8.8) and therefore are electronically very stable and reluctant to undergo chemical reactions. On the other hand, Group 7 Halogen atoms have one electron short of a Noble Gas electron arrangement (e.g. 2.7 or 2.8.7). These atoms do their best to gain an eighth electron to complete the outer sub-shell either by gaining an electron (ionic bond) or sharing an electron pair (covalent bond). This energetic desire to get that 8th outer electron makes these elements very reactive.

  • Q4 The displacement equations are:

    • chlorine + potassium iodide ===> potassium chloride + iodine

    • Cl_2(aq) +   2KI_(aq) ===>  2KCl_(aq) + I_2(aq)  (balanced)

    • and ....

    • bromine + potassium iodide ===> potassium bromide + iodine

    • Br_2(aq) +   2KI_(aq) ===>  2KBr_(aq) + I_2(aq)  (balanced)

  • Q5 The ionic redox equations are, in terms of words and symbols are:

    • chlorine molecule + iodide ion ===> chloride ion + iodine

    • Cl_2(aq) +  2I^-_(aq) ===> 2Cl^-_(aq) + I_2(aq)  (balanced)

    • The chlorine is reduced by electron gain and the iodide ion is oxidised by electron loss.

    • and ...

    • bromine molecule + iodide ion ==> bromide ion + iodine

    • Br_2(aq) +  2I^-_(aq) ==>  2Br^-_(aq) + I_2(aq)  (balanced!)

    • The bromine molecule is reduced by electron gain and the iodide ion is oxidised by electron loss.

  • Q6 All the elements in a group have the same outer electron configuration which is the main factor in determining an elements chemistry.

  • Q7 When a halogen atom reacts, it gains an electron to form a singly negative charged ion e.g. Cl + e^-  ==> Cl^- which has a stable noble gas electron structure like argon. (2.8.7 ==> 2.8.8)

    • As you go down the group from one Group 7 halogen element down to the next .. F => Cl => Br => I ...

      • the atomic radius gets bigger due to an extra filled electron shell,

      • the outer electrons are further and further from the nucleus and are also shielded by the extra full electron shell of negative electron charge,

      • therefore the outer electrons are less and less strongly attracted by the positive nucleus as would be any 'incoming' electrons to form a halide ion (or shared to form a covalent bond).

    • SO, this combination of factors means to attract an 8th outer electron is more and more difficult as you go down the group, so the element is less reactive as you go down the group, i.e. less 'energetically' able to form the X^- ion (halide ion) with increase in atomic number.

• TASK 3: The electrolysis of sodium chloride solution (brine)

  • Q1a Water is a covalent liquid and there virtually no ions to carry an electric current.

  • Q1b When acids or salts etc. are dissolved in water the solution then contains lots of ions and it is these charged particles which carry an electric current as they move through the solution when a potential difference (voltage) is applied.

  • Q2 With the current ON you will see gas bubbles forming on the electrode. As soon as the current is switched OFF the electrode reactions cease and no bubbling is seen.

  • Q3a Gas 1 (formed at cathode -ve electrode) squeaky pop with a lit splint is the test for hydrogen.

  • Q3b Gas 2 (formed at anode +ve electrode) turns blue litmus red but rapidly bleaches the paper white. This is a simple test for chlorine.

  • Q3c The universal indicator in the solution turns blue-purple, showing an alkali is formed, which must be sodium hydroxide.

  • Q3d (i) Starch solution gives a blue-black colour with iodine. (ii) Since chlorine can be formed by electrolysis of sodium chloride, in principle iodine could be produced by electrolysis of a solution of a salt of iodine e.g. aqueous potassium iodide.

  • Q4a Positive ions move towards the negative electrode (- cathode) and these will be hydrogen ion H⁺ and sodium ion Na⁺. The hydrogen ions become hydrogen gas.

  • Q4b The hydrogen ions are reduced by electron gain to form hydrogen gas molecules.

    • 2H⁺_(aq) + 2e^- ===> H_2(g)

  • Q4c Negative ions move towards the positive electrode (+ anode) and these will be the hydroxide ion OH^- and the chloride ion Cl^-. The chloride ions become chlorine gas.

  • Q4d The chloride ion is oxidised by electron loss to form chlorine gas molecules.

    • 2Cl^- - 2e^- ===> Cl_2(g) or it can be written as 2Cl^- ===> Cl_2(g) + 2e^-

  • Q4e The ions left are hydroxide OH^- and sodium Na⁺, these can be extracted to form the extremely useful alkali sodium hydroxide NaOH.

• TASK 4: The uses of Halogens and their compounds

  • Q1 Chlorine is a powerful disinfectant and kills most all bacteria.

  • Q2 Uses of chlorine: PVC plastic manufacture, chlorinated hydrocarbons (organo-chlorine compounds) are used as solvents, pesticides and disinfectants like TCP (trichlorophenol). It is combined with hydrogen to make hydrogen chloride which is dissolved in water to manufacture hydrochloric acid. Chlorine is used in the manufacture of household bleach, industrial bleaches for cotton, linen, wood pulp and domestic cleaners.

  • Q3 Hydrogen is used in the hydrogenation of unsaturated vegetable oils to make 'solid' margarine. It is combined with chlorine to form hydrogen chloride which is dissolved in water to make hydrochloric acid.

  • Q4 Sodium hydroxide is used in oven cleaners and drain cleaners. detergents, soaps, and making sodium salts from acids including soluble aspirin since aspirin is an insoluble organic acid.

  • Q5a Silver salts are used in photographic film e.g. silver chloride, silver bromide and silver iodide.

  • Q5b/c They are chemically changed by visible light (and ultra-violet and X-rays too) to form silver.

  • Q6a hydrogen + chlorine ==> hydrogen chloride, which is a colourless acidic gas.

  • Q6b When dissolved in water hydrochloric acid is formed and the solution has a pH of about 1.

  • Q6c It is a strong acid and reacts with alkalis to form chloride salts.

  • Q6d Hydrogen bromide and hydrogen iodide.

  • Q6e They will be like hydrogen chloride (Group 7 connection - Periodic Table pattern) i.e. colourless acidic gases that will dissolve in water to form acids. These acids will be neutralised by alkalis to form bromide or iodide salts.

4. The Extraction of Metals (original task sheet)

• Answers not done yet

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