📚 Chemistry for the IB Diploma: Core Principles | IB化学文凭课程核心原理
The IB Diploma Programme Chemistry course develops a deep understanding of matter and its interactions through a coherent set of core concepts. Mastering these fundamentals – atomic structure, bonding, stoichiometry, energetics, kinetics, equilibrium, acids and bases, redox, and organic chemistry – provides the essential framework for both Standard and Higher Level studies. This article walks through the key core principles, linking theory to the quantitative and qualitative skills required by the syllabus.
IB文凭课程化学通过一系列连贯的核心概念，培养学生对物质及其相互作用的深刻理解。掌握原子结构、化学键合、化学计量、能量学、动力学、平衡、酸碱、氧化还原和有机化学这些基本内容，为标准和高级水平的学习构建起必要的知识框架。本文将梳理关键核心原理，将理论与教学大纲要求的定量和定性技能联系起来。
1. Atomic Structure | 原子结构
Atoms consist of a central nucleus containing protons and neutrons, surrounded by electrons in discrete energy levels. The atomic number Z defines the element, while the mass number A is the total number of nucleons. Isotopes of an element differ in neutron number and can be identified using mass spectrometry. Electrons occupy orbitals described by quantum numbers, with the electron configuration following the Aufbau principle, Hund’s rule and the Pauli exclusion principle. The electromagnetic spectrum provides evidence for quantized energy levels, as absorption and emission lines correspond to electron transitions between shells.
原子由包含质子和中子的中心原子核以及分立的能级上的电子组成。原子序数 Z 定义了元素，质量数 A 是核子的总数。元素的同位素因中子数不同而异，可通过质谱进行鉴定。电子占据由量子数描述的原子轨道，电子排布遵循构造原理、洪德规则和泡利不相容原理。电磁波谱为量子化能级提供了证据，因为吸收和发射谱线对应于电子在壳层之间的跃迁。
- Subatomic particles: proton (p, relative mass 1, charge +1), neutron (n, mass 1, charge 0), electron (e⁻, mass 1/1836, charge –1)
- 次原子粒子：质子 (p, 相对质量 1, 电荷 +1), 中子 (n, 质量 1, 电荷 0), 电子 (e⁻, 质量 1/1836, 电荷 –1)
- Emission spectra: lines converge at higher energy; E = hν connects energy and frequency
- 发射光谱：谱线在高能端收敛；E = hν 联系能量和频率
- Orbitals: s (spherical), p (dumbbell, 3 orientations), d (5 orbitals) – each holds max 2 electrons
- 轨道：s (球形), p (哑铃形, 3种取向), d (5个轨道) – 每个最多容纳2个电子
2. Stoichiometric Relationships | 化学计量关系
f substance containing exactly 6.02214076 × 10²³ entities, links the particle scale to measurable masses. Empirical and molecular formulas are derived from percentage composition and molar mass data. Balanced equations provide the mole ratios needed for limiting reactant, theoretical yield and percentage yield calculations. Solution stoichiometry involves concentration (mol dm⁻³), and gas stoichiometry applies the ideal gas equation PV = nRT.
化学计量学处理化学反应中反应物与产物之间的定量关系。摩尔定义为精确含有 6.02214076 × 10²³ 个微粒的物质的量，将粒子尺度与可测质量联系起来。实验式和分子式可从百分组成和摩尔质量数据推导得出。配平的方程式提供了计算限量反应物、理论产量和产率所需的摩尔比。溶液化学计量涉及浓度 (mol dm⁻³)，气体化学计量则应用理想气体方程 PV = nRT。
| Concept | Formula / Relation |
| Molar mass M | M = m / n (g mol⁻¹) |
| Number of particles N | N = n × L (L = 6.02×10²³ mol⁻¹) |
| Concentration c | c = n / V (mol dm⁻³) |
| Ideal gas equation | PV = nRT |
| Percentage yield | (actual yield / theoretical yield) × 100% |
3. Chemical Bonding and Structure | 化学键合与结构
Chemical bonding determines the structure and properties of substances. Ionic bonding involves electrostatic attraction between oppositely charged ions formed by electron transfer, often between metals and non‑metals. Covalent bonding arises from the sharing of electron pairs between non‑metal atoms, described by Lewis structures, VSEPR theory and hybridization. Metallic bonding is a lattice of positive ions delocalised in a sea of electrons. Intermolecular forces – London dispersion, dipole‑dipole and hydrogen bonding – govern physical properties such as boiling points and solubility. The structure of solids can be giant (network covalent, ionic, metallic) or simple molecular, which directly affects volatility and conductivity.
化学键合决定了物质的结构和性质。离子键是由电子转移形成的带相反电荷的离子之间的静电吸引，通常发生在金属与非金属之间。共价键来自非金属原子之间共享电子对，可通过路易斯结构、VSEPR理论和杂化轨道加以描述。金属键是正离子在电子海中离域形成的晶格。分子间作用力——伦敦色散力、偶极‑偶极力和氢键——决定着沸点和溶解度等物理性质。固体的结构可以是巨型（网络共价、离子、金属）或简单分子，这直接影响揮发性和导电性。
- Electronegativity difference > 1.7 usually implies ionic bonding; smaller difference gives polar covalent bonds
- 电负性差 > 1.7 通常意味着离子键；差值较小则形成极性共价键
- VSEPR: electron pairs repel, leading to shapes such as linear (180°), trigonal planar (120°), tetrahedral (109.5°), bent, and trigonal pyramidal
- VSEPR：电子对互斥，产生直线形 (180°)、三角形 (120°)、四面体形 (109.5°)、弯曲形和三角锥形等形状
- Hydrogen bonding: occurs with N, O, F attached to H; responsible for the unusual properties of water and the secondary structure of proteins
- 氢键：与N、O、F相连的H可形成；是水异常性质和蛋白质二级结构的原因
4. Energetics and Thermochemistry | 能量学与热化学
ΔH°, 298 K, 100 kPa). Exothermic reactions release heat (ΔH negative), while endothermic reactions absorb heat (ΔH positive). Hess’s Law states that the total enthalpy change for a reaction is independent of the pathway, enabling the calculation of ΔH from enthalpy of formation or combustion data. Bond enthalpies provide average values for bond breaking/forming but are less accurate. Calorimetry experiments determine ΔH using q = mcΔT, and standard enthalpy changes of neutralisation, solution, and hydration are examined.
热化学研究化学反应过程中的能量变化。反应的焓变 ΔH 在标准条件下 (ΔH°, 298 K, 100 kPa) 测量。放热反应释放热量 (ΔH 为负)，吸热反应吸收热量 (ΔH 为正)。盖斯定律指出，反应的总焓变与途径无关，因此可以利用生成焓或燃烧焓数据计算 ΔH。键焓提供了断裂和形成化学键的平均能量值，但精确度较低。量热实验通过 q = mcΔT 测定 ΔH，同时还会考察标准中和焓、溶解焓和水合焓。
ΔH°rxn = Σ ΔH°f(products) – Σ ΔH°f(reactants)
q = m c ΔT
- Hess’s Law cycle: construct an enthalpy diagram with alternative routes, keeping arrows in consistent directions
- 盖斯定律循环：构建具有不同路径的焓图，保持箭头方向一致
- Average bond enthalpy: ΔH ≈ Σ(bonds broken) – Σ(bonds formed); less reliable because bond energies depend on molecular environment
- 平均键焓：ΔH ≈ Σ(断裂键的键焓) – Σ(形成键的键焓)；因键能依赖于分子环境而可靠性较低
5. Kinetics | 化学动力学
Chemical kinetics explores the rates of reactions and the factors that influence them. The rate of a reaction is typically expressed as the change in concentration of a reactant or product per unit time. Collision theory states that reacting particles must collide with sufficient energy (greater than activation energy Eₐ) and correct orientation. Factors affecting rate include temperature, concentration (or pressure for gases), surface area of solids, and the presence of a catalyst. A catalyst provides an alternative reaction pathway with a lower activation energy, increasing the rate without being consumed. The Maxwell‑Boltzmann distribution shows the range of kinetic energies and explains why only a fraction of collisions lead to a reaction.
化学动力学探究反应的速率及其影响因素。反应速率通常表示为反应物或产物浓度在单位时间内的变化。碰撞理论指出，反应粒子必须以足够的能量（大于活化能 Eₐ）和正确的取向碰撞。影响速率的因素有温度、反应物浓度（或气体压强）、固体表面积以及催化剂的存在。催化剂提供了一条活化能更低的替代反应途径，从而加快反应速率而本身不被消耗。麦克斯韦‑玻尔兹曼分布显示了分子动能的范围，解释了为什么只有一部分碰撞能引发反应。
- Rate = k [A]ᵐ [B]ⁿ; orders m,n determined experimentally, not from stoichiometry
- 速率方程：速率 = k [A]ᵐ [B]ⁿ；级数 m, n 由实验测定，而非源自化学计量数
- Maxwell‑Boltzmann: increasing temperature shifts the distribution to higher energies, and more molecules exceed Eₐ
- 麦克斯韦‑玻尔兹曼：升高温度使分布向高能区移动，超过 Eₐ 的分子比例增大
- Catalysts: heterogeneous (different phase) and homogeneous (same phase); examples include iron in Haber process and enzymes in biological systems
- 催化剂：多相催化剂（不同相）和均相催化剂（同一相）；实例包括哈伯法中的铁和生物系统中的酶
6. Chemical Equilibrium | 化学平衡
reactions are equal, so macroscopic properties remain constant. The equilibrium constant K꜀ brium. Le Chatelier’s principle predicts the direction of shift when a system at equilibrium is subjected to a change in concentration, pressure or temperature. The magnitude of K indicates the extent of reaction; a very large K favours products. The relationship ΔG° = –RT ln K links equilibrium to thermodynamics.
许多反应是可逆的，能达到动态平衡状态，此时正向和逆向反应速率相等，宏观性质保持恒定。平衡常数 K꜀（溶液）或 Kₚ（气体）表示平衡时产物与反应物浓度以其化学计量数为指数的比值。勒夏特列原理可预测平衡体系在受到浓度、压力或温度变化时的移动方向。K 值的大小反映了反应进行的程度；K 值很大时有利于产物。关系式 ΔG° = –RT ln K 将平衡与热力学联系起来。
aA + bB ⇌ cC + dD K꜀ = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ
- Le Chatelier: adding reactant shifts equilibrium to products; for gaseous systems, increasing pressure favours the side with fewer gas moles
- 勒夏特列：增加反应物使平衡向产物方向移动；对于气体体系，增大压强有利于气体分子总数较少的一侧
- Catalysts do not affect equilibrium position; they only speed up the attainment of equilibrium
- 催化剂不影响平衡位置；它们只加快达到平衡的速率
- Temperature change is the only factor that alters the value of K (exothermic: K decreases with T increase)
- 温度变化是唯一能改变 K 值的因素（放热反应：T升高，K减小）
7. Acids and Bases | 酸和碱
The Brønsted– on acceptors. In aqueous solutions, the pH scale reflects hydrogen ion concentration: pH = – ly ionise, establishing an equilibrium described by Kₐ or Kᵦ. The ionic product of water K𝓌 weak base and conjugate acid), resist changes in pH upon addition of small amounts of acid or alkali. Acid‑ uce titration curves, with the equivalence point identified using indicators or pH meters.
布朗斯特‑劳里理论将酸定义为质子 (H⁺) 给予体，碱定义为质子接受体。在水溶液中，pH标度反映氢离子浓度：pH = –lg[H⁺]。强酸和强碱完全解离；弱酸和弱碱部分电离，并建立起由 Kₐ 或 Kᵦ 描述的平衡。水的离子积 K𝓌 = [H⁺][OH⁻] = 1.0×10⁻¹⁴ (298 K) 使得能计算碱性溶液的 pH。缓冲溶液由弱酸及其共轭碱（或弱碱及其共轭酸）组成，能在加入少量酸或碱时抵抗 pH 的变化。酸碱滴定产生滴定曲线，利用指示剂或 pH 计来确定等当点。
| Formula | Relationship |
| pH = –log[H⁺] | pOH = –log[OH⁻]; pH + pOH = 14 (at 25°C) |
| K꜀ = [H⁺][A⁻]/[HA] | pK꜀ = –log K꜀ |
| Henderson–Hasselbalch | pH = pK꜀ + log([A⁻]/[HA]) (for buffer design) |
8. Redox Processes | 氧化还原过程
Redox reactions involve transfer of electrons. Oxidation is loss of electrons; reduction is gain of electrons (OIL RIG). Oxidation states (oxidation numbers) are assigned to atoms to track electron transfer. In a balanced redox reaction, the increase in oxidation number equals the decrease. Half‑equations separate the oxidation and reduction processes. Electrochemical cells convert chemical energy into electrical energy (voltaic cells) or use electrical energy to drive non‑spontaneous reactions (electrolytic cells). The standard electrode potential E° for a half‑cell, measured against the standard hydrogen electrode, predicts the direction of electron flow and the feasibility of a reaction: a positive cell potential E°cell indicates a spontaneous process. The Nernst equation adjusts potentials for non‑standard conditions.
氧化还原反应涉及电子转移。氧化是失去电子，还原是获得电子 (OIL RIG)。为追踪电子转移，可给原子赋予氧化数（氧化态）。配平的氧化还原反应中，氧化数的增加值等于减少值。半反应式将氧化和还原过程分开描述。电化学电池要么将化学能转化为电能（原电池），要么利用电能驱动非自发反应（电解池）。以标准氢电极为参比测得的半电池标准电极电势 E°，可预测电子流向和反应的可行性：正值的电池电势 E°cell 表明过程自发。能斯特方程用于非标准条件下的电势校正。
- Rules for oxidation states: free element = 0; simple ion = charge; oxygen usually –2; hydrogen +1 with non‑metals, –1 with metals
- 氧化数规则：游离态元素为0；简单离子等于电荷数；氧通常为–2；氢与非金属结合为+1，与金属结合为–1
- Electrochemical series: species with more negative E° are stronger reducing agents; those with more positive E° are stronger oxidizing agents
- 电化序：E° 越负的物种还原性越强；E° 越正的物种氧化性越强
- Electrolysis: in aqueous solutions, competing half‑reactions at the electrodes are decided by comparing E° values and considering kinetic factors
- 电解：在水溶液中，电极上竞争性的半反应通过比较 E° 值并考虑动力学因素来确定
9. Organic Chemistry | 有机化学
Organic chemistry focuses on carbon‑based compounds, characterized by functional groups that determine chemical behaviour. The homologous series (alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, amines, etc.) have general formulas and show gradual trends in physical properties. IUPAC nomenclature systematically names organic molecules. Key reaction types include addition (alkenes), substitution (alkanes, alcohols with hydrogen halides), oxidation (primary and secondary alcohols), esterification (carboxylic acid + alcohol) and condensation polymerisation. Stereoisomerism – both geometrical (cis‑trans) and optical isomerism – is crucial in biochemistry and medicines. Reaction mechanisms, such as SN1 and SN2 for nucleophilic substitution, are covered at Higher Level.
有机化学以碳基化合物为核心，其特征官能团决定了化学行为。同系列（烷烃、烯烃、醇、醛、酮、羧酸、胺等）具有通式，物理性质呈现渐变趋势。IUPAC命名法系统命名有机分子。关键反应类型包括：加成（烯烃）、取代（烷烃、醇与卤化氢）、氧化（伯醇和仲醇）、酯化（羧酸 + 醇）和缩聚反应。立体异构——几何异构（顺‑反）和旋光异构——在生物化学和药物中至关重要。像亲核取代的 SN1 和 SN2 等反应机理在高级水平中学习。
- Functional groups: hydroxyl –OH, carbonyl C=O (aldehyde: end carbon, ketone: middle carbon), carboxyl –COOH, amino –NH₂
- 官能团：羟基 –OH，羰基 C=O (醛：末端碳，酮：中间碳)，羧基 –COOH，氨基 –NH₂
- electrophilic addition; bromine water test: decolourisation of orange bromine confirms C=C
- 烯烃发生亲电加成；溴水试验：橙色溴水褪色可确认 C=C 双键
- Primary alcohols oxidize to aldehydes then carboxylic acids; secondary alcohols oxidize to ketones; tertiary alcohols resist oxidation
- 伯醇氧化生成醛再成羧酸；仲醇氧化成酮；叔醇不易被氧化
10. Measurement and Data Processing | 测量与数据处理
cant digit. The number of significant figures reflects precision. Systematic errors affect accuracy, while random errors affect precision. Data can be processed by calculating mean, standard deviation, and percentage error. Graphical analysis frequently involves linearization to determine unknown quantities, e.g., the activation energy from an Arrhenius plot. Spectroscopic techniques, such as IR and mass spectrometry, identify functional groups and determine molecular structure. Uncertainty propagation through calculations must follow the rules for addition/subtraction and multiplication/division.
可靠的实验数据是化学分析的基础。所有测量都带有不确定度，以末位有效数字的±值表示。有效数字的位数反映精密度。系统误差影响准确度，偶然误差影响精密度。可通过计算平均值、标准差和百分误差来处理数据。图形分析常采用线性化方法来测定未知量，例如由阿伦尼乌斯图求算活化能。光谱技术，如红外光谱和质谱，可鉴定官能团并确定分子结构。计算过程中的不确定度传递须遵守加减法和乘除法的规则。
- reading ±0.05 cm³; percentage uncertainty = (absolute uncertainty / measured value) × 100%
- 滴定管的绝对不确定度为 ±0.05 cm³；百分不确定度 = (绝对不确定度 / 测量值) × 100%
- Arrhenius equation: ln k = ln A – Eₐ/(RT); plot ln k vs 1/T gives slope = –Eₐ/R
- 阿伦尼乌斯方程：ln k = ln A – Eₐ/(RT)；作 ln k 对 1/T 图得到斜率 = –Eₐ/R
- IR absorption: O–H broad around 3200–3600 cm⁻¹, C=O sharp around 1700–1750 cm⁻¹, C–O around 1000–1300 cm⁻¹
- 红外吸收：O–H 宽峰约在3200–3600 cm⁻¹，C=O 尖峰约1700–1750 cm⁻¹，C–O 约1000–1300 cm⁻¹
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