JC2 Chemistry Tutor Hougang

Why does Group 2 carbonate thermal stability increase down the group while Group 17 oxidising power decreases? JC2 students often know both trends but confuse the explanations: carbonate stability depends on how strongly a metal cation polarises the carbonate ion, whereas halogen oxidising power relates to redox tendencies and appropriate standard electrode potentials. Treating every periodic trend as simply ‘atomic radius gets bigger’ is not enough to earn a convincing H2 Chemistry explanation.

For JC2 Chemistry tuition in Hougang, H2 A-Level syllabus 9476 asks students to compare Group 2 reducing ability, Group 17 oxidising strength, carbonate decomposition and hydrogen halide thermal stability. It also includes Group 17 volatility, where stronger induced-dipole attractions down the group explain changes in physical state and boiling point. These topics are connected by periodicity but need different models for different observations.

This is a guide to the chemistry, the exam language and the scientific judgement behind the trends. eduKateSG’s three-student small-group tutorials operate from our centre at 8 Fourth Avenue near Sixth Avenue MRT, rather than a Hougang classroom. Parents should confirm current class placement, timetable and travel before making tuition plans.

The 2027 syllabus defines which groups to compare

The official SEAB H2 Chemistry 9476 syllabus for 2027 describes the relevant Group 2 elements from magnesium to barium and Group 17 elements from chlorine to iodine. It requires explanation of trends in radius, ionisation energy and electronegativity, the Group 17 volatility trend, and comparative redox reactivity using electrode potentials. Its chemical stability objectives include Group 2 carbonates and Group 17 hydrides, whose explanations involve different structural principles.

Students should not automatically bring fluorine or beryllium trends into an explanation aimed at the specified range. Those elements can be scientifically interesting, but the school syllabus chooses particular comparisons. Label any extra enrichment clearly and learn the named syllabus examples first. A short, accurate explanation of the required range is more useful than a broad list of half-remembered facts.

Across a period is not down a group

Moving down Group 2 or Group 17 adds occupied electron shells, increases shielding and generally increases the size of the atoms or relevant ions. That differs from the across-period pattern where increasing proton number changes attraction within a common outer shell. Before writing any explanation, the learner should check whether the question moves down a vertical group or across the horizontal Period 3 row.

This matters because ‘greater nuclear charge’ can sound persuasive while failing to account for increased shielding and distance. A correct trend discussion identifies the competing effects and which is dominant for the property being considered. The number of protons is only one part of the explanation. Use the actual quantity—ionisation energy, ionic size or electronegativity—rather than a generic phrase about atoms becoming more reactive.

Why Group 2 atoms become larger down the group

Magnesium, calcium, strontium and barium occupy successively lower periods. Their valence electrons are in shells with increasing principal quantum number, and there is greater shielding by inner electrons. The average distance of the outer electrons from the nucleus increases. Atomic radius therefore generally increases down the group, despite the concurrent rise in nuclear charge.

Students should say which electrons are being considered. The size of a neutral atom is not identical to the radius of its doubly charged cation, although both can show related trends. If a problem asks about carbonate stability, it is the polarising influence of M²⁺ that matters, so the relevant radius is the metal cation radius rather than only the neutral atomic radius.

Why Group 2 first ionisation energy generally decreases

The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous singly charged cations. Going down Group 2, the outer electron is further from the nucleus and more shielded, making it easier to remove despite the higher nuclear charge. The overall first ionisation energy therefore generally decreases from magnesium to barium.

That does not mean every chemical property can be explained solely by the first ionisation energy. Reduction potentials and aqueous reactions also involve other energy contributions such as atomisation and hydration. The value of the ionisation trend is to explain one step in electron removal, not to replace a complete thermodynamic comparison of metal reactivity.

Group 2 metals as reducing agents

A reducing agent donates electrons and is itself oxidised. For Group 2 metals, a useful half-equation is M(s) → M²⁺(aq) + 2e⁻, representing oxidation. A metal whose relevant standard reduction potential M²⁺/M is more negative is thermodynamically more capable of reducing suitable oxidants under the standard-state model. The syllabus asks students to deduce relative reducing ability from appropriate electrode-potential data.

A positive or negative number should always be read with the half-reaction as written. Electrode tables normally list reductions, so a highly negative reduction potential corresponds to a favourable tendency in the reversed oxidation direction relative to suitable couples. It does not directly tell the reaction rate or whether a metal’s protective surface prevents visible reaction in a particular experiment.

The trend in reducing power needs context

Group 2 metals generally become stronger reducing agents down the specified range under the usual periodic comparison. Their outer electrons are more readily removed as shielding and distance increase, but the quantitative aqueous standard potentials involve several thermodynamic steps. A careful H2 response should use the given E° data when supplied instead of assuming a numerical order from ionisation energies alone.

Students often use the word ‘reactive’ without saying whether they mean reduction potential, visible reaction speed, reaction with water or ease of oxidation. Those are different measures. In an examination, identify whether the instruction asks for thermodynamic reducing ability or a practical reaction observation. A tutor should train students to explain what the data can actually establish.

Thermal decomposition of Group 2 carbonates

On sufficiently strong heating, Group 2 metal carbonates can decompose as MCO₃(s) → MO(s) + CO₂(g), producing the corresponding oxide and carbon dioxide. The decomposition conditions vary among the carbonates. The syllabus asks for the trend in thermal stability, which generally increases down the group from magnesium toward barium. A more thermally stable carbonate resists decomposition until more demanding conditions.

Do not confuse this process with melting. Thermal decomposition creates new chemical substances; melting changes the physical state without changing the formula of the material itself. The reaction equation helps identify which type of change is being discussed. An unchanged sample that simply liquefies cannot be described as having produced CO₂ without further evidence.

Why a smaller Group 2 cation destabilises carbonate

Each Group 2 cation carries a 2+ charge, but its radius increases down the group. A smaller cation such as Mg²⁺ has higher charge density and exerts a greater polarising effect on the large carbonate anion. This distortion can make the carbonate’s bonding more susceptible to decomposition into the oxide and carbon dioxide when heated. Down the group, the larger cations are less polarising, so the carbonates tend to be more thermally stable.

A weak explanation says ‘barium is bigger, so its carbonate is stronger’. A better one names the metal cation, charge density, distortion of CO₃²⁻ and the resulting resistance to thermal decomposition. The student’s reasoning should link a microscopic electrostatic feature to the chemical trend being measured. That is what separates an explanation from a remembered direction arrow.

MgCO₃ versus BaCO₃: the exam comparison

Magnesium carbonate is typically less thermally stable than barium carbonate under the relevant comparison. The Mg²⁺ cation is smaller and more strongly polarising, so it distorts the carbonate ion more strongly; Ba²⁺ is larger and less strongly polarising, making the carbonate relatively more resistant to decomposition. Both contain carbonate and both metal ions have charge +2, so cation charge does not change across the comparison.

Students who write ‘Ba²⁺ has a higher charge’ have invented a distinction that does not exist. A useful exercise is to underline the variable that truly differs: ionic radius. Then write a two-sentence explanation linking radius to polarising power and thermal stability. This removes excess words while preserving the chemistry required by an H2 marking point.

Carbonate decomposition and an evidence table

A practical-data question might compare the temperatures or heating conditions at which different carbonates begin to give detectable CO₂. The student should interpret the reported evidence carefully and recognise that apparatus, sample size and heating conditions affect observations. A qualitative trend can be deduced when the data genuinely support it, but an isolated temperature reading does not automatically provide a precise thermodynamic value.

Ask whether the question reports a decomposition temperature, the proportion decomposed after a fixed time or simply whether gas was observed. Those are different measurements. An effective conclusion mentions the actual variable measured, and an explanation supplies the relevant carbonate polarisation model. This habit prevents students from converting a broad stability principle into an unjustified numerical prediction.

Why Group 17 elements are oxidising agents

A halogen molecule can accept electrons to form halide ions, for example Cl₂ + 2e⁻ → 2Cl⁻. Because the halogen gains electrons, it acts as an oxidising agent, while the other reacting species loses electrons and is oxidised. The comparative oxidising ability of chlorine, bromine and iodine can be understood from their appropriate standard reduction potentials under the specified conditions.

Do not confuse the oxidation of a halide ion with oxidation by a halogen molecule. I⁻ can behave as a reducing agent when it loses electrons to form I₂; I₂ can act as an oxidising agent when it gains electrons to form I⁻. The relevant species and direction determine the label, not the word iodine by itself.

Oxidising power of chlorine, bromine and iodine

Under the standard school comparison, oxidising power decreases from Cl₂ through Br₂ to I₂. Their reduction potentials for X₂/2X⁻ become less positive down the group. Chlorine is therefore capable of oxidising bromide and iodide ions under appropriate conditions, while bromine can oxidise iodide. The reverse displacement directions are not favoured under the same standard thermodynamic argument.

This is a different trend from the Group 17 elements’ rising boiling temperatures. Oxidising power describes electron acceptance in a redox process, whereas boiling point depends strongly on intermolecular attraction in the molecular element. A student who explains both with one vague word ‘reactivity’ has failed to choose the correct model.

Worked chlorine–bromide displacement

The reaction Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ is an oxidation–reduction process. Bromide ions lose electrons to become bromine, while chlorine molecules gain electrons to become chloride. Charge and atom balance should be checked: two bromides on the left, one Br₂ on the right, two chlorines on both sides, and overall charge −2 on both sides.

An illustrative standard-potential comparison uses E°(Cl₂/Cl⁻) around +1.36 V and E°(Br₂/Br⁻) around +1.07 V, giving E°cell approximately +0.29 V for chlorine reduction coupled with bromide oxidation. Use the question’s supplied values and conventions rather than memorised approximations. A positive potential supports thermodynamic favourability under standard conditions, not a guarantee of an instantaneous visible colour change.

Worked bromine–iodide displacement

The reaction Br₂ + 2I⁻ → 2Br⁻ + I₂ shows bromine oxidising iodide ions. With approximate standard reduction potentials of +1.07 V for Br₂/Br⁻ and +0.54 V for I₂/I⁻, the calculated standard cell potential for the direction shown is around +0.53 V. The direction is supported by the relative potentials. The exact values and conditions in the exam should control the calculation.

Students sometimes subtract the numbers in the wrong direction because they treat both half-equations as reduction steps in the overall reaction. Identify which species actually gains electrons and which loses them. Write the overall balanced reaction first, then use the cathode-reduction minus anode-reduction potential relationship. The same method works for unfamiliar redox couples.

Halide reducing strength increases down Group 17

Whereas halogen oxidising power decreases down the group, the halide ions generally become stronger reducing agents from chloride to iodide in the relevant comparison. I⁻ can lose electrons more readily relative to suitable oxidants than Cl⁻ under the model, consistent with the contrasting redox potentials. This reversal of the trend is not a contradiction: halogen molecules and halide ions are different chemical species participating in opposite electron-transfer directions.

When a student sees ‘chlorine’, they should check whether the formula means Cl₂ or Cl⁻. If the paper asks which substance is oxidised in a displacement reaction, it is often the halide ion. If it asks which is the oxidising agent, it is the electron-accepting halogen molecule. Correct species identification comes before every verbal comparison.

Group 17 volatility and induced-dipole attractions

Chlorine, bromine and iodine are simple molecular substances whose molecules become larger and more polarisable down the group. The magnitude of instantaneous dipole–induced dipole attractions generally increases, requiring more energy to separate molecules. Their melting and boiling temperatures consequently tend to rise, and their ordinary room-condition appearances progress from gas through liquid to solid in the familiar sequence.

Do not claim that the covalent X–X bond inside a halogen molecule is broken during boiling. The phase change primarily overcomes attractions between molecules. This distinction between intramolecular bonding and intermolecular forces is an essential explanation skill and helps prevent transferring bond-energy logic to the wrong physical process.

Why iodine is less volatile than chlorine

I₂ has a larger, more easily polarised electron cloud than Cl₂, so stronger dispersion attractions can form between its molecules. More energy is needed to separate iodine molecules into the gas phase under comparable conditions, giving its lower volatility and higher boiling and sublimation tendencies. The explanation requires the link between polarisability and intermolecular attraction, not merely the statement that iodine has more electrons.

A student who writes ‘iodine has stronger covalent bonds, so it is solid’ has selected the wrong attraction. The covalent bond holds iodine atoms within an I₂ molecule, while the relevant physical-state comparison concerns attractions among different I₂ molecules. Ask the learner to draw two separate molecules and indicate which interaction is overcome during boiling.

Hydrogen halide thermal stability

The hydrogen halides HCl, HBr and HI have different bond energies. Moving down from HCl to HI, the H–X bond becomes longer and generally weaker, so the thermal stability of the hydrogen halide decreases. The relevant explanation concerns the covalent hydrogen–halogen bond that must be broken in decomposition. This is not the same physical process as boiling Cl₂, Br₂ or I₂.

Students who use increasing dispersion forces to explain hydrogen-halide thermal decomposition are confusing intermolecular attraction with intramolecular bond strength. A good comparison explicitly names H–Cl, H–Br and H–I bonds and connects decreasing bond energy to easier decomposition when sufficiently heated. The syllabus expects this bond-energy explanation, not a claim that larger molecules always decompose faster under all circumstances.

Hydrogen halide thermal stability is not aqueous acid strength

Thermal stability concerns resistance to decomposition of the hydrogen halide molecule under heating. Aqueous acid strength concerns proton donation in water and involves solvation and equilibrium. HCl, HBr and HI behave as strong acids in ordinary aqueous school contexts, while their H–X bond strengths differ markedly. One topic should not be substituted for the other merely because both contain an H–X bond.

Read the actual question: is it asking for bond dissociation, stability on heating, or hydronium concentration in solution? The model and available evidence differ. A one-line memorised ordering may point in the right direction but still fail to explain the named property. Teaching students to identify the property first can save marks across much of physical and inorganic Chemistry.

A comparison of three trends using one table

Make three distinct columns: Group 17 molecular boiling points increase down the group, halogen oxidising power decreases, and hydrogen-halide thermal stability decreases. Under each heading write the cause. Boiling points: increased polarisability and stronger induced-dipole attractions. Oxidising power: relative reduction tendencies and E° values. Thermal stability: weaker H–X bonds. The directions may be memorised, but the chemical explanations must remain separate.

Then remove the cause column and ask the learner to rebuild it from the measured quantity. If they choose a bond-energy explanation for molecular boiling, correct the attraction type. If they choose dispersion-force language for E° values, return to electron transfer. This exercise reveals exactly why generic trend slogans are dangerous.

Comparing Group 2 and Group 17 electron transfer

Group 2 metals act as reducing agents by donating electrons, while Group 17 molecules act as oxidising agents by accepting them. An illustrative overall reaction between a suitable Group 2 metal and a halogen produces an ionic metal halide, with electron transfer from the metal to the halogen. The relative tendencies are influenced by the specific substances and conditions, and standard potentials are useful evidence for thermodynamic comparisons.

Do not assume an intensely exothermic reaction is necessarily safe or fast under every physical condition. Some metal–halogen reactions require strict control and can be hazardous. At JC2 the learning goal is to balance electron transfer, recognise the roles and use suitable evidence rather than perform unsupervised reactions.

Carbonates and the environmental context

Thermal decomposition of carbonates is relevant to industrial mineral processing and production of materials such as lime from limestone. For example, CaCO₃ → CaO + CO₂ generates carbon dioxide and requires heat input. Understanding the reaction connects stoichiometry and energetics with the question of industrial emissions. It does not mean every discussion can be reduced to a single claim that all carbonate products are bad for the environment.

Real sustainability assessment includes energy sources, process efficiency, capture or use of CO₂, alternative materials and the service provided by the final product. JC2 learners can practise a disciplined approach: first state the balanced reaction, then identify where emissions arise, and finally describe what extra evidence is needed to compare solutions. Chemistry informs public decisions when its limitations are made visible.

Worked carbonate mass calculation

Suppose 0.100 mol of CaCO₃ decomposes completely according to CaCO₃(s) → CaO(s) + CO₂(g). The balanced equation predicts 0.100 mol of CO₂. Using an approximate molar mass of 44.0 g mol−1 for CO₂, that corresponds to 4.40 g of carbon dioxide. If a gas volume is requested, the student must additionally use the stated temperature and pressure, not automatically insert an unlabelled molar gas volume.

This elementary calculation matters because an integrated H2 problem may combine Group 2 stability with gas-law or emissions data. The decomposition reaction gives the mole ratio, and a separate physical model translates moles into mass or volume. Students who understand the sequence can handle unfamiliar industrial contexts without memorising a special formula for each one.

A seven-session revision route

Session one covers Group 2 electron configurations, radii and ionisation trends. Session two tackles reducing power and electrode potentials. Session three focuses on the carbonate decomposition equation and cation polarisation explanation. Session four treats halogen displacement and half-equations. Session five compares volatility and dispersion attractions. Session six covers hydrogen-halide bond strengths and thermal stability. Session seven integrates unseen data requiring the student to select among the models.

The plan can be extended over two weeks if JC2 subjects and school commitments demand it. Each session should include an altered question without a chapter label. A student who can explain a new comparison after several days is demonstrating more durable learning than one who reads the same trend table immediately before answering.

Check the halogen displacement direction before calculating E°

Suppose a question gives the standard reduction potentials for chlorine and iodine and asks whether Cl₂ can oxidise iodide ions. First write the candidate reaction Cl₂+2I⁻→2Cl⁻+I₂. Chlorine undergoes reduction, while iodide undergoes oxidation. Only then calculate the standard cell potential using the two reduction values as tabulated. The higher chlorine reduction potential makes the overall standard potential positive under the stated approximation.

Students who reverse the reaction but keep the same positive cell potential have mixed a chemical direction with its thermodynamic sign. When a reaction is reversed, the cell potential changes sign. Writing the half-equations as reductions in the data table and identifying which is reversed in the actual overall equation makes the logic transparent.

A stronger oxidant does not imply a faster visible reaction

A more positive standard reduction potential can support a greater thermodynamic tendency to accept electrons, but it does not by itself determine the activation barrier or speed of a real reaction. A student may correctly infer that chlorine can oxidise bromide under standard thermodynamic reasoning and still be unable to predict an exact observed reaction time from those potentials alone. Temperature, concentration, mixing and mechanisms can affect kinetics.

This distinction is especially important when the question uses the word ‘reactivity’. Ask whether the paper requests reducing or oxidising *power* from E° values, or the measured *rate* of an observed process. One number cannot answer both questions without additional evidence. The same reasoning helps with fuel cells, batteries and catalysts.

A carbonate stability comparison with a common charge

All the metal cations in the specified Group 2 carbonate comparison are doubly charged. Their charge number does not rise down the group. The important change is ionic radius: Mg²⁺ is relatively small and more strongly polarising, whereas Ba²⁺ is larger and less strongly polarising. This changes the distortion of the carbonate ion and is a key part of the school-level explanation for increasing thermal stability.

If the learner writes that barium carbonate is more stable because the barium ion has ‘more charge’, ask them to identify the actual ionic charges in MgCO₃ and BaCO₃. Both are +2 for the metal and −2 for carbonate. Correcting the fundamental variable before adding more theory often resolves the whole misconception.

The reverse reaction does not have the same enthalpy sign

Thermal decomposition of a carbonate is represented as MCO₃→MO+CO₂. If an energy question provides an enthalpy change for that reaction, forming the carbonate from the oxide and carbon dioxide is the exact reverse process under matching conditions and has the opposite enthalpy sign. The basic Hess’s Law rule remains valid even when the question is dressed in a periodic-trend context.

Students should distinguish the thermodynamic reaction enthalpy from the kinetic temperature at which decomposition becomes observable. A higher practical decomposition temperature is useful evidence of greater thermal stability, but a single data point does not supply every enthalpy term. Identify what was measured before deriving a conclusion.

Group 17 physical state is evidence of molecular forces

At ordinary room conditions, chlorine is a gas, bromine a liquid and iodine a solid. This pattern is consistent with increasing melting and boiling temperatures down the group as dispersion attractions become stronger. The molecules are diatomic, and the relevant phase changes involve interactions between molecules. The observation alone tells us about physical state; the induced-dipole model explains the trend.

Try showing a student only the physical states, then ask for a causal explanation. If they say iodine has more electrons, ask how that affects electron-cloud polarisability and thus intermolecular attraction. That extra causal link is often where explanation marks reside. Accurate Chemistry connects a structural feature to a measured property.

Thermal stability and acid strength must be separated

HCl, HBr and HI differ in H–X bond energies, and their resistance to decomposition on heating decreases down the group. In water, however, they are commonly described as strong acids in the ordinary school context, with proton transfer and hydration relevant to the observed acidity. It is therefore wrong to claim that the most thermally stable hydrogen halide must necessarily produce the highest hydrogen-ion concentration in any aqueous sample.

A well-prepared student starts by naming the property in the question: bond dissociation, thermal stability, equilibrium acidity or solution concentration. Then they use the matching model. This habit allows them to handle questions that deliberately juxtapose two seemingly conflicting orders without falling back on a generic word such as strength.

Halogen molecules and halide ions must not be swapped

The symbol Cl₂ refers to a neutral diatomic molecule; Cl⁻ refers to a negatively charged ion. Their electron-transfer tendencies are opposite sides of a redox couple. A halogen molecule acts as an oxidising agent when reduced; a halide ion can be oxidised by a suitable oxidant, acting as a reducing agent. The specific direction must be shown in an equation.

A learner who writes ‘iodine is easily oxidised’ without specifying I₂ or I⁻ has left the chemistry ambiguous. Train them to write the complete formula and charge in every comparative sentence. This small discipline prevents mistakes not only in Group 17 but also in electrochemistry more broadly.

A safe example of evidence from a displacement experiment

In a properly supervised school laboratory, halogen displacement can be studied through observations of the reaction mixture and appropriate controls. Colours can be affected by solvent, concentration and other species, so an observation should be recorded with context rather than reduced to an unqualified one-word rule. The oxidation and reduction half-equations provide a separate check on the inferred process.

A desk-based tutor can work with teacher-supplied observations and ask which redox direction is supported. That teaches deduction without needing to handle reactive halogens. Parents should not interpret a paper exercise as permission for home experimentation; these substances and reagents require laboratory safety procedures.

Three distinct mechanisms behind three Periodic Table trends

Take the carbonate stability, halogen oxidising strength and halogen volatility trends side by side. The first depends on polarising power of cations acting on carbonate; the second concerns electron transfer and standard electrode potentials; the third depends on induced-dipole attractions between molecules. All are related to atomic and electronic structure, but no single one-line rule explains them all.

In an examination, underline the measured property first. Then select the appropriate microscopic explanation. If the property is thermal decomposition of an ionic carbonate, do not begin with dispersion forces. If the property is boiling of a simple molecular halogen, do not rely on the ionisation-energy trend of a metal. Model selection is a major part of chemistry mastery.

How to write an evidence-based ‘deduce’ response

Suppose the question provides standard reduction potentials and asks whether bromine can oxidise iodide. State the overall reaction, select bromine reduction and iodide oxidation, calculate the resulting cell potential from the given values and interpret the positive sign under the appropriate conditions. Merely writing ‘bromine is more reactive’ omits the evidence trail and leaves the type of reactivity unclear.

If the question instead provides carbonate heating data, the response should identify the observed stability order and explain it using charge density and polarisation. Different datasets support different kinds of deduction. Practise matching the response type to the information supplied rather than attaching one memorised paragraph to every question containing a Group number.

A tutor’s error ledger for Group 2 and 17

Use a five-column record: question source, first wrong move, scientific correction, changed follow-up, delayed outcome. Errors might include treating carbonate breakdown as melting, giving the wrong halogen displacement direction, describing iodine boiling in terms of covalent X–X bonds, or claiming Ba²⁺ carries a greater charge than Mg²⁺. Naming each mistake accurately points toward an effective correction.

In a three-student class, different learners can work on different comparisons before explaining them to the group. The tutor should require independent answers after the discussion. A student who can later solve an unfamiliar redox comparison or stability trend without being told which formula to use has gained a transferable skill, not merely a corrected worksheet.

Why understanding is worth more than a perfect trend chart

A trend chart can be useful as a summary, but it is not mastery unless the learner can explain the causation when the order is reversed, extended or embedded in unfamiliar data. Strong JC2 Chemistry revision alternates retrieval of key trends with short explanation questions and changed numerical examples. The student should be able to state not only which way a property moves, but why that model predicts the direction.

Ask them to compare two examples after a few days without notes. If they can identify the appropriate ions, molecules, electron-transfer direction or bond-energy trend, the learning has begun to stick. If they can only remember the arrow direction while the explanation has vanished, revisit the underlying structure instead of enlarging the flashcard collection.

Frequently asked questions about Groups 2 and 17

Why do Group 2 carbonates become more stable down the group? Larger M²⁺ ions have lower charge density and polarise CO₃²⁻ less strongly. Which Group 17 element is the strongest oxidising agent among chlorine, bromine and iodine? Chlorine in the usual standard comparison. Why does iodine have a higher boiling point? Larger, more polarisable molecules experience stronger induced-dipole attractions. Is HCl more thermally stable than HI? Yes, in the relevant H–X bond-energy comparison.

Are halide reducing agents ordered the same as halogen oxidising agents? No; electron donation and electron acceptance are opposite tendencies. Does E° predict reaction speed? No, it addresses thermodynamic tendencies under standard conditions. Does thermal decomposition mean melting? No, chemical species change. Is Group 2 the same as Period 3? No; the direction on the Periodic Table and the underlying comparison differ.

JC2 Chemistry Tutor Hougang | H2 Group 2 Carbonates and Group 17 Halogen Trends