AQA · GCSE · Chemistry

All substances are made of atoms 原子 — the smallest part of an element that can exist. Each element has a chemical symbol (O, Na, …); about 100 elements exist, shown in the periodic table.

Compounds 化合物 form when elements combine chemically in fixed proportions; they are represented by formulae and can only be separated back into elements by chemical reactions. Chemical reactions always form one or more new substances, often with a detectable energy change. Equations: word equations and symbol equations with balanced formulae; (HT) balanced half-equations and ionic equations.

Mixtures 混合物: two or more elements or compounds not chemically combined; each substance keeps its properties. Separated by physical processes only — no new substances:

• filtration 过滤 — insoluble solid from liquid;
• crystallisation 结晶 — dissolved solid from solution;
• simple distillation 蒸馏 简单蒸馏 — liquid from dissolved solid (and solvents);
• fractional distillation 分馏 — liquids with different boiling points;
• chromatography 色谱法 — soluble substances in a mixture.

Development of the atom model: atoms were first thought to be indivisible spheres → the electron's discovery gave the plum pudding model 布丁模型 (ball of positive charge with negative electrons embedded) → the alpha-scattering experiment showed mass and positive charge concentrated in a central nucleus (nuclear model) → Bohr: electrons orbit at specific distances → protons identified in the nucleus → Chadwick: the neutron 中子. New evidence changes or replaces models.

In an atom protons = electrons, so no overall charge. Atomic number = protons; mass number = protons + neutrons. Atoms of the same element with different neutron numbers are isotopes 同位素. Atom radius ≈ 0.1 nm (1 × 10⁻¹⁰ m); the nucleus is less than 1/10 000 of that. Almost all mass is in the nucleus.

Relative atomic mass (Ar) averages over the isotopes' abundance — calculate it from percentage abundances. Electronic structure: electrons fill the lowest levels first — sodium is 2,8,1; represent the first twenty elements both as numbers and diagrams.

The table orders elements by atomic (proton) number 原子序数, so that elements with similar properties fall in groups (columns). For main-group elements, group position reflects outer-shell electrons 最外层电子 and similar chemical properties; helium has two outer electrons, while the other Group 0 elements have eight. Explain an element's position from its electronic structure; predict probable reactivity from position.

Development: early tables ordered by atomic weight — incomplete, with some elements misplaced. Mendeleev left gaps for undiscovered elements and sometimes changed the order; his predicted elements were found, supporting his table. Isotopes later explained why atomic-weight order was sometimes wrong.

Metals and non-metals: metals usually lose electrons to form positive ions; many non-metals gain electrons to form negative ions or share electrons in covalent bonds. Metals sit left and lower; non-metals right and upper. Know the characteristic physical and chemical differences, and link atomic structure to position.

Group 0 — noble gases: unreactive — stable outer-shell arrangements (8 outer electrons; helium 2), so they do not easily form molecules. Boiling points increase down the group (with relative atomic mass).

Group 1 — alkali metals: one outer electron. Reactions of Li, Na, K with oxygen, chlorine and water (e.g. 2 Na + 2 H₂O → 2 NaOH + H₂). Reactivity increases down the group — the outer electron is lost more easily further from the nucleus.

Group 7 — halogens: seven outer electrons; non-metals, diatomic molecules (Cl₂, Br₂, I₂). Reactivity decreases down the group; melting and boiling points increase. A more reactive halogen displaces 置换 a less reactive one from a salt solution (chlorine displaces bromine from potassium bromide).

Compared with Group 1, the transition elements (exemplify with Cr, Mn, Fe, Co, Ni, Cu) have higher melting points, densities, strength and hardness, and are less reactive with oxygen, water and halogens.

Typical properties: ions with different charges (Fe²⁺/Fe³⁺), coloured compounds, and use as catalysts 催化剂 (iron in the Haber process).

Three strong chemical bonds, all explained by electrostatic forces:

• Ionic 离子键 — a metal atom transfers outer electrons to a non-metal: metal atoms lose electrons to become positive ions; non-metal atoms gain them to become negative ions; Groups 1/2 metals and 6/7 non-metals form ions with noble-gas electronic structures. Draw the electron transfer with dot and cross diagrams; deduce ion charges from group number (Group 1 → +1, Group 2 → +2, Group 6 → −2, Group 7 → −1).
• Covalent 共价键 — non-metal atoms share pairs of electrons. Know dot-and-cross diagrams for H₂, Cl₂, O₂, N₂, HCl, H₂O, NH₃, CH₄, and line representations for small molecules, polymer repeating units and giant covalent structures.
• Metallic 金属键 — a giant lattice of metal atoms with delocalised outer electrons 游离电子 free to move through the whole structure; the sharing of these electrons gives strong metallic bonding.

Know the limitations of models: dot-and-cross, ball-and-stick, 2D and 3D diagrams all simplify — no forces shown, fixed bond lengths, giant structures drawn as small fragments. Deduce empirical formulae from lattice models; molecular formulae from molecule diagrams.

States of matter: solid, liquid, gas; melting/freezing at the melting point, boiling/condensing at the boiling point. Particle theory (small solid spheres) explains the changes; the stronger the forces between particles, the higher the melting/boiling points. (HT) The simple model's limits: no forces shown, all spheres, solid particles. State symbols: (s), (l), (g), (aq).

Larger molecules → stronger intermolecular forces → higher melting/boiling points. Alloys 合金 are harder than pure metals because different-sized atoms distort the layers, stopping them sliding.

• Diamond — a giant covalent structure 巨型共价结构 in which each carbon forms four covalent bonds: very hard, very high melting point, does not conduct.
• Graphite — each carbon forms three bonds, layers of hexagonal rings with no covalent bonds between layers (soft, slippery — lubricant); one delocalised electron per atom → conducts electricity like a metal.
• Graphene — a single layer of graphite: one atom thick, strong, conducts — electronics and composites.
• Fullerenes — hollow molecules of carbon hexagons (plus 5- or 7-membered rings); Buckminsterfullerene C₆₀ 富勒烯 is spherical. Carbon nanotubes 碳纳米管 — cylindrical fullerenes with huge length-to-diameter ratios: nanotechnology, electronics, materials.

Nanoscience = structures 1–100 nm (a few hundred atoms). Nanoparticles 纳米颗粒 are smaller than fine particles (PM2.5, 100–2500 nm), which are smaller than coarse particles/dust (PM10, 1 × 10⁻⁵–2.5 × 10⁻⁶ m).

Surface area : volume: as a cube's side decreases 10×, SA:V increases 10×. Nanoparticles may have different properties from the bulk material because of this high ratio — catalysts (smaller quantities work), medicine delivery, cosmetics, electronics. Concerns: effects inside the body and in the environment are not fully known.

Conservation of mass 质量守恒: no atoms are lost or made, so the mass of products equals the mass of reactants. Symbol equations are balanced in atom numbers; know the difference between a multiplier before a formula (numbers of units) and a subscript within it (atoms in the unit).

Relative formula mass (Mr) 相对分子质量 = sum of the relative atomic masses in the numbers shown. In a balanced equation, ΣMr of reactants = ΣMr of products. Percentage by mass of an element = (Ar × number of atoms ÷ Mr) × 100 %.

Mass changes with gases: metal + oxygen → oxide gains mass; thermal decomposition of a carbonate loses the escaped CO₂ — no law is broken once the gas is counted.

Uncertainty: every measurement carries uncertainty; use the range of repeated measurements about the mean as its estimate (and mean ± range/2 in calculations).

The mole 摩尔: the mass of one mole of a substance in grams is numerically its Mr. One mole contains the Avogadro constant 阿伏伽德罗常数 of particles — 6.02 × 10²³ — the same count of stated particles (atoms, molecules, ions) as a mole of any other substance.

Equations as mole ratios: Mg + 2 HCl → MgCl₂ + H₂ reads "1 mol Mg reacts with 2 mol HCl → 1 mol MgCl₂ + 1 mol H₂". Given any one mass, calculate all others: mass → moles → ratio → moles → mass.

Balancing from masses: convert each mass to moles, divide by the smallest, clear fractions to whole numbers.

Limiting reactant 限量反应物: the reactant completely used up limits the product; an excess of the other ensures completion. Calculate the product from the limiting reactant's moles only.

Concentration 浓度: in g/dm³ for all tiers — mass of solute in a given volume; (HT) also mol/dm³: moles = concentration × volume(dm³), rearranged as needed.

Percentage yield 产率 is below 100 % because: the reaction is reversible; product is lost on separation; reactants react in unwanted ways.

Atom economy 原子经济 measures how much of the starting material ends up in the useful product — high atom economy matters for sustainability and cost:

(HT) calculate the theoretical mass from the balanced equation, then the yield.

Concentration in mol/dm³ links moles, mass and volume: moles = C × V; from a titration 滴定, knowing the volumes of both solutions and one concentration gives the other — moles of acid = moles of alkali at neutralisation (respect the ratio in the equation).

• Metals differ in how easily they lose electrons — the reactivity series 活动性顺序 orders them, drives displacement 置换 and decides how each is extracted.
• Acids donate H⁺; alkalis donate OH⁻; their reaction makes a salt 盐 — and the salt's name reads off the acid and the base.
• Electrolysis forces ions to give up or take electrons at electrodes — extracting the most reactive metals and splitting solutions.

Reactivity series (learn the order): potassium, sodium, lithium, calcium, magnesium, [carbon], zinc, iron, [hydrogen], copper. Reactivity = the metal's tendency to form positive ions.

• With water: K, Na, Li, Ca react ( fizzing, hydroxide + hydrogen); Mg very slow; Zn/Fe/Cu no reaction.
• With dilute acids: Mg, Zn, Fe react → salt + hydrogen; Cu does not.
• A more reactive metal displaces a less reactive one from its compound: Zn + CuSO₄ → ZnSO₄ + Cu.

Extraction: unreactive metals (gold) occur native; metals below carbon are extracted by reduction 还原 with carbon (loss of oxygen); metals above carbon need electrolysis 电解. Identify oxidation 氧化 (gain of oxygen) and reduction (loss of oxygen).

(HT) Redox in electrons: oxidation is loss of electrons, reduction is gain — OIL RIG. Write ionic equations for displacement: Zn + Cu²⁺ → Zn²⁺ + Cu.

Acids neutralised by alkalis (soluble hydroxides) and bases (insoluble oxides/hydroxides) → salt + water; by metal carbonates → salt + water + carbon dioxide. The acid decides the salt's negative ion: hydrochloric → chlorides, nitric → nitrates, sulfuric → sulfates; the base supplies the positive ion. Predict products and write salt formulae from ion charges.

Making a soluble salt (RP1): add the insoluble solid (metal oxide/carbonate) to warm dilute acid until no more dissolves (excess solid proves completion), filter off the excess, evaporate to the crystallisation point and leave to crystallise; dry the crystals.

pH scale: 0–14, measured with universal indicator or a pH probe; 7 neutral, <7 acid, >7 alkaline. Acids give H⁺(aq); alkalis give OH⁻(aq). Neutralisation 中和: H⁺ + OH⁻ → H₂O.

(Chem) Titrations 滴定 (RP2): measure reacting volumes of a strong acid and strong alkali accurately — burette, pipette, indicator; (HT) calculate concentrations in mol/dm³ and g/dm³ (topic 3.4 methods).

(HT) Strong and weak acids: strong acids (HCl, HNO₃, H₂SO₄) are completely ionised; weak acids (ethanoic, citric, carbonic) are partially ionised. Same concentration → stronger acid → lower pH. Each pH unit down multiplies [H⁺] by 10. Dilute/concentrated = amount of substance per volume — different axis from strong/weak.

Electrolytes 电解质: molten or dissolved ionic compounds — ions free to move, so they conduct. Positive ions → cathode (negative); negative ions → anode (positive); ions are discharged as elements.

• Molten binary compounds (lead bromide): metal at the cathode, non-metal at the anode.
• Extraction (aluminium): electrolysis of molten Al₂O₃ + cryolite — the mixture lowers the melting point, saving energy; carbon anode burns away (with the oxygen produced) and must be replaced. Electrolysis is used when the metal is too reactive for carbon reduction.
• Aqueous solutions (RP3): at the cathode, hydrogen is produced if the metal is more reactive than hydrogen (else the metal deposits); at the anode, oxygen — unless halide ions are present, when the halogen forms.

(HT) Half-equations 半方程 — balance charge with electrons:

• cathode: Cu²⁺ + 2e⁻ → Cu; 2H⁺ + 2e⁻ → H₂
• anode: 2Cl⁻ → Cl₂ + 2e⁻; 4OH⁻ → O₂ + 2H₂O + 4e⁻

• Exothermic 放热 reactions give energy out — the surroundings warm; endothermic 吸热 reactions take it in — they cool.
• Reaction profile 反应能量图s show the activation energy 活化能 and the overall change; (HT) bond energies add up the same story.
• Chemical cells and fuel cell 燃料电池s (chemistry only) turn reaction energy into electricity.

Energy is conserved: energy transferred to the surroundings comes off the products' store. An exothermic reaction transfers energy out — the surroundings' temperature rises (combustion, many oxidations, neutralisation; uses: hand warmers, self-heating cans). An endothermic reaction takes energy in — the temperature falls (thermal decomposition, citric acid + sodium hydrogencarbonate; uses: sports injury packs). Judge each from the temperature change of the surroundings; ΔH calculations are not required.

Reaction profiles: reactions need colliding particles with at least the activation energy. Draw and read energy-level diagrams — relative energies of reactants and products, the activation energy arrow from the reactants' level, the overall energy change, curved line between. Exothermic: products below reactants; endothermic: products above.

(HT) Bond energies 键能: energy is supplied to break reactant bonds and released when product bonds form:

• exothermic — forming releases more than breaking costs;
• endothermic — breaking costs more than forming releases.

Overall change = Σ(bond energies broken) − Σ(bond energies formed). A catalyst lowers the activation energy — it does not change the overall energy change.

RP4: investigate the variables affecting temperature changes in reacting solutions (e.g. volume/concentration) — plan variables, measure ΔT, plot, conclude.

Cells contain chemicals that react to produce electricity. The voltage depends on the type of electrode and electrolyte; a simple cell is two different metals in an electrolyte — the more reactive metal produces the higher voltage (it releases electrons more readily). Batteries = cells in series for greater voltage.

Non-rechargeable 可充电 (alkaline) cells stop when a reactant runs out; rechargeable cells reverse their reactions when an external current is supplied.

Fuel cells: fuel (e.g. hydrogen) + oxygen supplied continuously; the fuel is oxidised electrochemically to give a potential difference. Overall: hydrogen → water. Evaluate against rechargeable batteries: no pollutants at point of use, continuous refuel; but hydrogen storage, production and cost weigh against. (HT) half-equations for the hydrogen fuel cell:

• negative electrode: 2 H₂ → 4 H⁺ + 4e⁻ (or 2 H₂ + 4 OH⁻ → 4 H₂O + 4e⁻)
• positive electrode: O₂ + 4 H⁺ + 4e⁻ → 2 H₂O (or O₂ + 2 H₂O + 4e⁻ → 4 OH⁻)

• Rate is a quantity per second — read it off tables, graphs and tangents; collision theory 碰撞理论 explains every factor that changes it.
• Reversible reactions settle into dynamic equilibrium 动态平衡; (HT) Le Chatelier predicts how each condition shifts it.
• Industry optimises rate and yield together — compromise conditions.

Calculating rates: rate of reaction 反应速率 = quantity of reactant used ÷ time, or product formed ÷ time — in g/s or cm³/s (HT also mol/s). Interpret product-vs-time graphs (steeper start, flattening as reactant runs out); draw tangents 切线 and use their gradient as the rate at that instant (HT calculate it).

Factors affecting rate: concentration (solution), pressure (gas), surface area (solid), temperature, catalyst 催化剂s. RP5: investigate concentration by (a) measuring the volume of gas produced and (b) observing a colour/turbidity change — hypothesis, variables, repeats.

Collision theory: reactions occur only when particles collide with at least the activation energy 活化能. Raising concentration/pressure crowds particles — more frequent collisions; smaller solid pieces raise the surface-area-to-volume ratio — more exposed surface, more frequent collisions; raising temperature gives particles more energy — more collisions AND more collisions that pass the activation energy.

Catalysts: change the rate but are not used up; each reaction has its own catalyst; enzymes are biological catalysts. A catalyst offers an alternative pathway with lower activation energy — identify it by speeding the reaction yet never appearing in the equation. Its reaction profile keeps the same overall energy change with a lower hump:

Reversible reactions 可逆反应: the products can react back to the reactants — written with the ⇌ arrow. If exothermic one way, endothermic the other, transferring the same amount of energy.

Equilibrium: in a closed system, equilibrium is reached when the forward and reverse rates are equal — the concentrations stop changing though both reactions continue (dynamic).

(HT) Le Chatelier's principle 勒夏特列原理: a system at equilibrium responds to counteract any change:

• concentration ↑ of a reactant → more product forms (and vice versa);
• pressure ↑ → the position moves to the side with fewer gas molecules;
• temperature ↑ → the position moves in the endothermic direction (↓ for exothermic direction).

A catalyst does not shift the position — it reaches equilibrium faster. Industry picks compromise conditions balancing rate, yield, safety and cost (e.g. the Haber process in topic 10).

• 原油 — 古代プランクトン生物量 — は分馏によって分離され、アルカン (CₙH₂ₙ₊₂) は燃料として燃焼する；クラッキングにより大きな分子を小さなアルカンと反応性の高いアルケン (CₙH₂ₙ) に変換する。
• アルケン、アルコール、カルボン酸（化学のみ）は、予見可能な反応を持つ官能基ファミリーである。
• ポリマー — 付加重合（アルケン単量体）および(HT) 縮重重合 — 自然由来のもの：タンパク質、デンプン、セルロース、DNA。

原油は岩石中に存在する有限資源であり、主に泥に埋没した古代の生物量（プランクトンなど）の遺骸である。ほぼ炭化水素（水素＋炭素のみ）からなる混合物であり、主としてアルカンで、一般式は CₙH₂ₙ₊₂：メタン、エタン、プロパン、ブタン（名称と化学式をすべての表記法で理解すること）。

分餾：画分は炭素数類似の分子を含み、塔の異なる高さにおける蒸発および凝縮によって分離される—小分子は上部（低沸点）、大分子は底部に位置する。画分は燃料（ガソリン、ディーゼル、灯油、重油、LPG）およびペトロchemicalsの原料—溶媒、潤滑油、ポリマー、洗剤—となる。

性質は分子サイズに依存：大きな分子 → 高い沸点、高い粘性、低い可燃性—各画分の用途に対応させる。

クラッキング：大きな炭化水素をより小さく有用な分子に分解する—触媒クラッキング（高温＋触媒）またはスチームクラッキング（高温＋蒸気）。生成物：小さなアルカン（燃料）＋アルケン（ポリマー原料）。アルケンは反応性が高く、臭素水を脱色する（橙色→無色）—アルケンの検出反応。与えられた化学式からクラッキングの化学方程式を平衡させる。

アルケン CₙH₂ₙ は C=C二重結合を含む—不飽和（同じ炭素数のアルカンより水素が2つ少ない）。成员：エチレン、プロピレン、ブテン、ペンテン。官能基の反応がそのファミリー全体の反応を与える：

• 燃焼 — だが 煙を伴う炎（不完全燃焼）；
• 水素との反応 → アルカン（ニッケル触媒）；水との反応 → アルコール（蒸気、ホスホン酸触媒）；ハロゲンとの反応 →ジハロアルカン（臭素水の試験）。

アルコール –OH：メタノール、エタノール、プロパノール、ブタノール。反応：ナトリウムとの反応（泡立ち、水素発生）；空気中での燃焼（清浄燃焼—燃料）；水への溶解；酸化（空気／酸化剤）→ カルボン酸。用途：燃料、溶媒、アルコール飲料。発酵：糖＋酵母 → 温かく、酸素のない条件でのエタノール水溶液。

カルボン酸 –COOH：メタノ酸、酢酸、プロパン酸、ブタン酸。炭酸塩と反応（泡立ち、CO₂発生）、水に溶解（弱酸性—HT：部分的に電離するため、強酸よりpHが高い）、アルコールと反応 → エステル（酢酸エチル）＋水。

付加重合：多くのモノマー（アルケン、C=Cを持つ）が一つに結合してポリマーになる—エチレンからポリエチレン、プロピレンからポリプロピレン。繰り返し単位はちょうど単体分子の原子をそのまま持つ—他は何も生成されない。描く：単体分子 → 二重結合を開いた繰り返し単位。

(HT) 縮合重合：各モノマーが2つの官能基を持ち、結合時に小さな分子（通常は水）を失う。2種類の異なるモノマーでそれぞれ同じ官能基が2つあるもの：例：エタン二醇＋ヘキサンジオ酸 → ポリエステル。アミノ酸（H₂N…COOH）が縮合 → ポリペプチド；一本鎖内で異なるアミノ酸 → タンパク質（グリシンが例示）。

天然ポリマー：DNA — 4種のヌクレオチドからなる2本のポリマー鎖による二重らせん；タンパク質（アミノ酸モノマー）、デンプン（糖）、セルロース（糖）。

• アルカンの名称/化学式 C1–C4；沸点・粘性・可燃性の傾向に基づく分餾の順序。
• クラッキングの条件、生成物および平衡化学方程式；臭素水の試験と変色。
• （化学）アルケンの官能基とその3つの付加反応；アルコールの4つの反応＋発酵の条件；カルボン酸の3つの反応。
• 単量体からの付加重合と逆反応；(HT)ポリエステルにおける縮合の原理；DNAヌクレオチド＋他の3つの天然ポリマーの単量体。

• 化学における純物質とは、元素または化合物のいずれか一つを指し、融点・沸点が一定であることで証明されます；調合（フォーミュレーション）は意図的な混合物です。
• クロマトグラフィーは相間での分配によって分離され、Rf値でスポットを同定します。
• 気体試験（H₂, O₂, CO₂, Cl₂）および（化学のみ）イオン試験——炎色反応、水酸化物沈殿、炭酸塩、ハロゲン化物、硫酸塩——これらが分析者のツールキットを構成します。

純物質 — 単一の元素または化合物であり、他と混合していません。純物質は特定の sharp（鋭い）温度で融解・沸騰します；混合物は範囲で融解します。融点・沸点データを用いて区別してください。（日常会話での「純粋」は不純物なしを意味するため、異なる用法です。）

調合（フォーミュレーション） — 有用な製品として設計された混合物で、各成分は目的に応じて厳密に計量されています：燃料、洗浄剤、塗料、医薬品、合金、肥料、食品。与えられた情報から一つを同定してください。

クロマトグラフィー — 固定相（紙）と移動相（溶媒）があります。分離は各物質の相間での分配に依存し、固定相への親和性が高いものほど低い位置に留まります。測定法：

異なる化合物は異なる溶媒で異なるRf値を示すため、同定に利用できます。純化合物はあらゆる溶媒で単一スポットを与えます。

炎色反応（陽イオン）：リチウム — 紅；ナトリウム — 黄色；カリウム — ラベンダー；カルシウム — オレンジレッド；銅 — 緑。混合物では色が互いに覆い隠される場合があります。

金属水酸化物（水酸化ナトリウム溶液）：Al³⁺, Ca²⁺, Mg²⁺は白色沈殿を生じますが、過剰のNaOHにおいてAl(OH)₃のみ溶解します；Cu²⁺ 青、Fe²⁺ 緑、Fe³⁺ 茶褐色の沈殿を生じます。

炭酸塩: 希酸を加える — 泡立ち；そのガスは石灰水を白く濁らせる。

ハロゲン化物: 希硝酸を加えてから硝酸銀を加える — **AgCl（白色）、AgBr（クリーム色）、AgI（黄色）**の沈殿が生成する。

硫酸塩: 希塩酸を加えてから塩化バリウムを加える — BaSO₄の白色沈殿ができる。

(HT) 炎発光分光法: 機器が線発光スペクトルを記録する。線の位置で金属を同定し、強度で濃度を判定する。炎色反応との違い：非常に感度が高く、混合物にも適用でき、迅速である点。

• 融点による純物質と混合物の区別；5つの配合物の名称を列挙せよ。
• クロマトグラムからRf値を計算せよ。なぜ純化合物は1つのスポットしか示さないのか説明せよ。
• ガスの4つの検出試験とそれぞれの結果。
• (Chem) 炎色反応；アルミニウム过量時の水酸化物色；炭酸塩／ハロゲン化物／硫酸塩の試薬と沈殿の色；(HT) 分光法の利点。

• The early atmosphere came from volcanic activity — its CO₂ steam-cooled to the oceans; photosynthesis 光合作用 (algae, plants) raised oxygen and buried carbon.
• Greenhouse gases — CO₂ and methane — trap radiation; human activity raises them and the global climate change 全球气候变化s.
• Pollutants from fuels — CO, SO₂, NOₓ, particulates 颗粒物 — each with a source, a chemistry and a consequence.

Theories: the early atmosphere cannot be known for certain — evidence comes from gases trapped in ancient ice and from other planets' atmospheres today. Intense volcanic activity released gases: mostly carbon dioxide, with water vapour, nitrogen and traces of methane and ammonia — little or no oxygen.

The water vapour condensed to form the oceans; CO₂ dissolved in them and was locked into carbonate sediments (shells). Over ~2.7 billion years, algae and plants photosynthesised, absorbing CO₂ and releasing oxygen — oxygen rose, CO₂ fell; much carbon was buried as fossil fuel 化石燃料s. Nitrogen, unreactive, accumulated to dominate today's air: about four-fifths N₂, one-fifth O₂, plus argon and ~0.04 % CO₂.

Greenhouse gases 温室气体 — carbon dioxide, methane and water vapour — absorb and re-emit some of the long-wavelength infrared radiation that the warm Earth radiates to space, keeping the surface warmer than it would otherwise be. The global climate change hypothesis says rising greenhouse-gas levels raise the average temperature.

Human causes: deforestation (less CO₂ absorbed), burning fossil fuels (more CO₂), cattle/rice and landfill (methane). Consequences discussed in the spec: melting ice, sea-level rise, changing rainfall and extreme weather. The scientific consensus rests on peer-reviewed evidence — interpret given data on temperature, CO₂ and methane over time.

Combustion of fuels releases:

• carbon monoxide (CO) — a toxic gas from incomplete combustion 不完全燃烧 in limited oxygen; binds haemoglobin, reducing oxygen transport;
• carbon particulates (soot) — also from incomplete combustion; worsen respiratory problems and cause global dimming;
• sulfur dioxide (SO₂) and oxides of nitrogen (NOₓ) — from impurities in fuel / nitrogen reacting at engine temperatures; cause acid rain 酸雨 (damaging trees, lakes, buildings) — removed from flue gases by neutralisation with alkalis (e.g. calcium oxide);
• NOₓ also forms at high engine temperatures from N₂ + O₂, and contributes to photochemical smog.

Complete combustion — plenty of oxygen — gives CO₂ and water only.

• Resources are used, reused and recycled; potable water 饮用水 — filtered and sterilised fresh water, or desalinated sea water — is the first essential.
• Life cycle assessment 生命周期评估s weigh a product's environmental cost stage by stage; reduce–reuse–recycle cuts every stage.
• (Chem) corrosion 腐蚀 prevention, alloys, ceramics/polymers/composite 复合材料s, and the Haber process 哈伯法's compromise chemistry.

Humans use the Earth's resources for warmth, shelter, food and transport; finite resources (ores, fossil fuels) are processed for energy and materials; renewable ones replenish. Sustainable development 可持续发展 meets present needs without compromising future generations.

Potable water — safe to drink: low dissolved salts and microbes — but not pure water (it contains dissolved substances).

In the UK, fresh rainwater is made potable by: choosing a source → filter beds → sterilising (with chlorine, ozone or UV light). Where fresh water is scarce, desalination — distillation or reverse osmosis — needs large amounts of energy.

Waste water (sewage) treatment: screening and grit removal → sedimentation (sewage sludge + effluent) → anaerobic digestion of the sludge → aerobic biological treatment of the effluent. Potable water is easiest from ground water, harder from waste, hardest (energy-wise) from salt water.

(HT) Alternative metal extraction — copper ores are scarce: phytomining (plants absorb metal compounds; harvest, burn to ash, extract) and bioleaching (bacteria produce leachate solutions of the metal compounds) avoid moving huge amounts of rock.

Corrosion — destruction of materials by chemical reaction with the environment (e.g. iron + oxygen + water → rust). Prevention: greasing, painting, coating (galvanising with zinc, which gives sacrificial protection 牺牲保护 — it corrodes in place of the iron even when scratched) and alloying (stainless steel). Aluminium resists corrosion by its own protective oxide layer.

Alloys: bronze (copper + tin), brass (copper + zinc); gold jewellery alloyed with silver/copper/zinc — purity in carats (24 = 100 %; 18 = 75 %). Steels — iron + carbon (+ metals): high-carbon steel strong but brittle; low-carbon steel softer, shaped easily; stainless steel (Cr, Ni) hard and corrosion-resistant; aluminium alloys low density (aircraft).

Ceramics, polymers, composites: soda-lime glass (sand + sodium carbonate + limestone), borosilicate glass (sand + boron trioxide — higher melting point); clay ceramics (pottery, bricks — shaped wet clay, then fired). Polymers depend on monomers and conditions — LD and HD poly(ethene) both from ethene. Thermosoftening polymers melt on heating (recyclable chains); thermosetting polymer 热固性聚合物 does not (cross-links). Composites — a matrix/binder surrounding a reinforcement (fibres/fragments); know examples (fibreglass, concrete, carbon-fibre).