CH01 Core Principles of Chemistry | 化学CH01核心原理

📚 CH01 Core Principles of Chemistry | 化学CH01核心原理

The International AS Chemistry Unit 1 (CH01) lays the foundation for all further study in chemistry. It covers the structure of atoms, the ways atoms bond, how we measure amounts of substance, the energy changes in reactions, and the fundamentals of organic chemistry. These core principles are essential for understanding the behaviour of matter, from simple salts to complex biological molecules. Mastering this unit gives you the tools to analyse reactions quantitatively, predict molecular shapes, and explain physical properties such as melting points and solubility.

国际AS化学第一单元（CH01）为化学的后续学习奠定基础。它涵盖原子结构、原子间的成键方式、物质的量的计量方法、反应中的能量变化以及有机化学的基本原理。这些核心原理对于理解从简单盐类到复杂生物分子的物质行为至关重要。掌握本单元能够让你定量分析反应、预测分子形状并解释熔点和溶解度等物理性质。

1. Atomic Structure and Isotopes | 原子结构与同位素

Atoms consist of a central nucleus containing protons and neutrons, surrounded by electrons in shells. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. The atomic number (Z) is the number of protons, which defines the element. The mass number (A) is the total number of protons and neutrons. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. For example, carbon-12 (¹²C) has 6 protons and 6 neutrons, while carbon-13 (¹³C) has 6 protons and 7 neutrons. Isotopes have identical chemical properties because they have the same electron configuration, but slightly different physical properties due to differences in mass.

原子由含有质子和中子的中心原子核以及核外分层排布的电子组成。质子带正电，中子不带电，电子带负电。原子序数（Z）是质子数，它定义了元素种类。质量数（A）是质子与中子的总数。同位素是指质子数相同而中子数不同的同种元素的原子。例如，碳-12（¹²C）有6个质子和6个中子，而碳-13（¹³C）有6个质子和7个中子。同位素具有相同的化学性质，因为它们具有相同的电子排布，但由于质量的差异，物理性质略有不同。

The relative atomic mass (Aᵣ) of an element is the weighted average mass of its isotopes relative to 1/12th the mass of a carbon-12 atom. The relative isotopic mass is simply the mass of one isotope on the same scale. Mass spectrometry can be used to determine the abundance of isotopes and to calculate Aᵣ. A typical mass spectrum shows peaks corresponding to each isotope, with relative intensity giving the abundance.

元素的相对原子质量（Aᵣ）是其各同位素相对于碳-12原子质量的1/12的加权平均质量。相对同位素质量仅指某一同位素在该标度下的质量。质谱法可用于测定同位素丰度并计算Aᵣ。典型的质谱图显示出对应每种同位素的峰，其相对强度表示丰度。

Isotope	Protons	Neutrons	% Abundance
³⁵Cl	17	18	75.8
³⁷Cl	17	20	24.2

Aᵣ(Cl) = (35 × 75.8 + 37 × 24.2) / 100 = 35.5

2. Electron Arrangement and Ionisation Energies | 电子排布与电离能

Electrons occupy atomic orbitals in shells and subshells. The principal quantum number n defines the shell. Subshells are labelled s, p, d, f. An s subshell holds a maximum of 2 electrons, p holds 6, d holds 10. Electrons fill orbitals starting from the lowest energy level, following the Aufbau principle. The order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d. For example, the electronic configuration of calcium (Z = 20) is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². The notation using noble gas shorthand is [Ar] 4s². Orbital box diagrams represent each orbital as a box and electrons as arrows with opposite spins (Hund’s rule).

电子占据原子轨道，这些轨道分属不同的电子层和亚层。主量子数n决定电子层。亚层标记为s、p、d、f。s亚层最多容纳2个电子，p亚层容纳6个，d亚层容纳10个。电子根据能量最低原理填充轨道，即从最低能级开始，顺序为：1s，2s，2p，3s，3p，4s，3d。例如，钙（原子序数20）的电子排布为1s² 2s² 2p⁶ 3s² 3p⁶ 4s²。用稀有气体简化写法表示为[Ar] 4s²。轨道方框图将每个轨道画为一个方框，电子用相反自旋的箭头表示（洪特规则）。

Ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge. First ionisation energy (IE₁) trends across a period generally increase due to increasing nuclear charge and similar shielding, which draws electrons more tightly. Down a group, IE₁ decreases because outer electrons are further from the nucleus and experience more shielding. Successive ionisation energies provide evidence for electron shells: a large jump indicates the removal of an electron from a new inner shell.

电离能是指从一摩尔气态原子中移去一摩尔电子形成一摩尔带单个正电荷的气态离子所需的能量。第一电离能（IE₁）在同周期中一般随着核电荷增加和相似的屏蔽效应而增大，使电子被束缚得更紧密。在同族中自上而下，第一电离能减小，因为外层电子离核更远且受到更多的屏蔽。逐级电离能为电子层的存在提供了证据：出现大幅跳跃意味着电子开始从新的内层移去。

3. Ionic, Covalent and Metallic Bonding | 离子键、共价键与金属键

Ionic bonding occurs between metals and non-metals by the transfer of electrons from the metal to the non-metal. The resulting positive and negative ions are held together by strong electrostatic forces in a giant ionic lattice. For example, sodium chloride (NaCl) consists of Na⁺ and Cl⁻ ions. Ionic compounds have high melting points, are brittle, and conduct electricity only when molten or dissolved because ions are free to move.

离子键形成于金属与非金属之间，由金属向非金属转移电子而形成。形成的正离子和负离子通过强大的静电引力结合成巨型离子晶格。例如，氯化钠（NaCl）由Na⁺和Cl⁻离子组成。离子化合物熔点高、脆性大，只有在熔融或溶解时才能导电，因为此时离子可以自由移动。

Covalent bonding involves the sharing of pairs of electrons between non-metal atoms. A single covalent bond (e.g., H–H) shares one pair of electrons; a double bond (e.g., O=O) shares two pairs; a triple bond (e.g., N≡N) shares three pairs. Covalent substances can exist as simple molecules (e.g., H₂O, CO₂) with weak intermolecular forces and low melting points, or as giant covalent structures (e.g., diamond, graphite, silicon dioxide) with strong covalent bonds throughout, giving very high melting points.

共价键涉及非金属原子之间共享电子对。单键（如 H–H）共享一对电子；双键（如 O=O）共享两对电子；三键（如 N≡N）共享三对电子。共价物质可以简单分子（如H₂O、CO₂）存在，分子间作用力弱，熔点低；也可以巨型共价结构（如金刚石、石墨、二氧化硅）存在，整个结构中遍布强共价键，因而熔点非常高。

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons. This bonding model explains the high electrical and thermal conductivity of metals (free electrons move), their malleability and ductility (layers of ions can slide over each other), and their high melting points.

金属键是正金属离子晶格与离域电子海之间的静电引力。这种键模型解释了金属的高导电性和导热性（自由电子移动）、延展性和可锻性（离子层可相互滑动）以及高熔点。

4. Electronegativity and Bond Polarity | 电负性与键的极性

Electronegativity is the ability of an atom to attract the bonding pair of electrons in a covalent bond. Fluorine is the most electronegative element (value 4.0 on the Pauling scale). In a bond between two identical atoms, the electron pair is shared equally – a non-polar covalent bond. When atoms of different electronegativities bond, the electron pair is pulled towards the more electronegative atom, creating a polar covalent bond with partial charges δ⁺ and δ⁻.

电负性是指原子在共价键中吸引成键电子对的能力。氟是电负性最大的元素（鲍林标度值为4.0）。在两个相同原子间形成的键中，电子对平等共享，即为非极性共价键。当电负性不同的原子成键时，电子对被拉向电负性较大的原子，形成带部分电荷δ⁺和δ⁻的极性共价键。

A dipole moment exists in a molecule if the bond polarities do not cancel out. Carbon dioxide (CO₂) has two polar C=O bonds, but the molecule is linear and symmetrical, so the dipoles cancel – it is non-polar overall. Water (H₂O) has bent shape and the O–H bond dipoles do not cancel, making it a polar molecule. Polarity affects physical properties such as solubility and boiling point.

如果键的极性不能相互抵消，分子就具有偶极矩。二氧化碳（CO₂）存在两个极性C=O键，但分子呈直线形对称，因此偶极相互抵消，整体为非极性分子。水（H₂O）分子呈弯曲形，O–H键的偶极不能抵消，使其成为极性分子。极性会影响溶解度和沸点等物理性质。

5. Intermolecular Forces and Physical Properties | 分子间作用力与物理性质

Intermolecular forces are forces between molecules. They are much weaker than covalent, ionic or metallic bonds. The three main types are: London (dispersion) forces, permanent dipole–dipole interactions, and hydrogen bonding. London forces arise from temporary fluctuations in electron distribution, creating instantaneous dipoles that induce dipoles in neighbouring molecules. They increase with the number of electrons and the surface area of the molecule, hence larger molecules have higher boiling points.

分子间作用力是分子之间的力，比共价键、离子键或金属键弱得多。主要有三种类型：伦敦（色散）力、永久偶极-偶极相互作用和氢键。伦敦力源于电子分布的瞬时涨落，形成瞬时偶极，并在相邻分子中诱导出偶极。它们随分子中的电子数和分子表面积的增加而增强，因此较大分子的沸点更高。

Permanent dipole–dipole forces occur between polar molecules and are additional to London forces. Hydrogen bonding is an especially strong type of dipole–dipole interaction that occurs when hydrogen is bonded to a very electronegative atom (N, O, or F) and is attracted to a lone pair on another such atom. Hydrogen bonding explains the unusually high boiling points of H₂O, NH₃ and HF compared to other hydrides in their groups, and is responsible for the structure of ice and the shape of DNA.

永久偶极-偶极力存在于极性分子之间，是伦敦力之外的作用力。氢键是一种特别强的偶极-偶极相互作用，当氢原子与一个电负性很强的原子（N、O或F）成键，并被另一个此类原子上的孤电子对所吸引时，便形成氢键。氢键解释了H₂O、NH₃和HF与其同族氢化物相比异常高的沸点，并决定了冰的结构和DNA的双螺旋形状。

6. The Mole Concept and Chemical Equations | 摩尔概念与化学方程式

The mole is the SI unit for amount of substance. One mole contains exactly 6.022 × 10²³ elementary entities (Avogadro constant). The molar mass (M) is the mass of one mole of a substance, with units g mol⁻¹, and is numerically equal to the relative atomic or formula mass. Using the mole concept, we can calculate reacting masses: n = m / M, where n is amount in mol, m is mass in g, M is molar mass.

摩尔是物质的量的国际单位。一摩尔恰好包含6.022 × 10²³个基本单元（阿伏伽德罗常数）。摩尔质量（M）是一摩尔物质的质量，单位为g mol⁻¹，其数值等于相对原子质量或相对式量。利用摩尔概念，我们可以计算反应中的质量：n = m / M，其中n为物质的量（mol），m为质量（g），M为摩尔质量。

A balanced chemical equation shows the stoichiometric ratios of reactants and products. For example, 2Mg(s) + O₂(g) → 2MgO(s) tells us that 2 mol of magnesium react with 1 mol of oxygen to produce 2 mol of magnesium oxide. Using these ratios, the mass of any reactant or product can be found. Percentage yield and atom economy are key indicators of reaction efficiency. Atom economy = (molar mass of desired product / sum of molar masses of all products) × 100%.

配平的化学方程式表示了反应物和生成物之间的化学计量比。例如，2Mg(s) + O₂(g) → 2MgO(s) 告诉我们2摩尔镁与1摩尔氧气反应生成2摩尔氧化镁。利用这些比例，可求出任何反应物或生成物的质量。产率和原子利用率是衡量反应效率的关键指标。原子利用率 =（目标产物的摩尔质量 / 所有产物摩尔质量之和）× 100%。

7. Empirical and Molecular Formulae from Combustion Data | 由燃烧数据求实验式与分子式

The empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule. Combustion analysis is a common method to determine empirical formula. A weighed sample of a hydrocarbon or organic compound is burned completely in excess oxygen. The masses of CO₂ and H₂O produced are measured. From these, the masses (and moles) of carbon and hydrogen can be calculated. The mass of any other element (e.g., oxygen) is found by difference.

实验式表示化合物中各原子最简整数比，而分子式表示一个分子中各元素原子的实际数目。燃烧分析是测定实验式的常用方法。精确称量的碳氢化合物或有机物样品在过量氧气中完全燃烧，测量生成的CO₂和H₂O的质量。由此可计算出碳和氢的质量（和物质的量），其他元素（如氧）的质量通过差减法求得。

After obtaining the moles of each element, divide by the smallest number of moles to get the empirical ratio. To find the molecular formula, the relative molecular mass (Mᵣ) of the compound is needed. This can be obtained from mass spectrometry or by using the ideal gas equation (for gases). The molecular formula is a whole-number multiple of the empirical formula: molecular formula = (empirical formula)ₙ, where n = Mᵣ / empirical formula mass.

得到各元素的物质的量后，除以最小物质的量，即得实验式的最简比。为了得到分子式，需要知道化合物的相对分子质量（Mᵣ），这可以通过质谱或气体理想气体方程获得。分子式是实验式的整数倍：分子式 = (实验式)ₙ，其中 n = Mᵣ / 实验式量。

8. Amount of Substance: Solutions and Gases | 物质的量：溶液与气体

Concentration of a solution is expressed in mol dm⁻³. The amount of solute (n) can be calculated using n = c × V, where c is concentration in mol dm⁻³ and V is volume in dm³. Stock solutions can be diluted using the dilution formula: c₁V₁ = c₂V₂. In titrations, the equivalence point is reached when the reactants have reacted in their stoichiometric ratio, and the unknown concentration can be found. Indicators or pH meters are used to detect the end point.

溶液的浓度以mol dm⁻³表示。溶质的物质的量（n）可用n = c × V计算，其中c为浓度（mol dm⁻³），V为体积（dm³）。储备溶液可用稀释公式c₁V₁ = c₂V₂进行稀释。在滴定中，当反应物按化学计量比完全反应时到达等当点，即可求出未知浓度。使用指示剂或pH计来检测滴定终点。

For gases, the ideal gas equation is pV = nRT, where p is pressure (Pa), V is volume (m³), n is amount of gas (mol), R is the gas constant (8.31 J K⁻¹ mol⁻¹), and T is temperature (K). At room temperature and pressure (RTP, 298 K and 101 kPa), one mole of any gas occupies approximately 24 dm³ (molar volume). This can be used to calculate the volume of gas produced in a reaction or to determine the Mᵣ of a volatile liquid.

对于气体，使用理想气体状态方程 pV = nRT，其中p为压力（Pa），V为体积（m³），n为气体物质的量（mol），R为摩尔气体常数（8.31 J K⁻¹ mol⁻¹），T为温度（K）。在常温常压下（RTP，298 K，101 kPa），一摩尔任何气体的体积约为24 dm³（摩尔体积）。利用这一关系可以计算反应生成的气体体积，或测定挥发性液体的相对分子质量。

9. Enthalpy Changes and Hess’s Law | 焓变与盖斯定律

Enthalpy change (ΔH) is the heat energy transferred in a reaction at constant pressure. Standard enthalpy changes are measured under standard conditions (100 kPa, 298 K, all substances in their standard states). Exothermic reactions release heat (ΔH is negative), while endothermic reactions absorb heat (ΔH is positive). The standard enthalpy of combustion (ΔH_c^⦵) is the enthalpy change when one mole of a substance is completely burned in excess oxygen. The standard enthalpy of formation (ΔH_f^⦵) is the enthalpy change when one mole of a compound is formed from its elements.

焓变（ΔH）是恒压条件下反应中传递的热能。标准焓变在标准条件下（100 kPa，298 K，所有物质处于标准状态）测定。放热反应释放热量（ΔH为负值），吸热反应吸收热量（ΔH为正值）。标准燃烧焓（ΔH_c^⦵）是一摩尔物质在过量氧气中完全燃烧时的焓变。标准生成焓（ΔH_f^⦵）是由元素生成一摩尔化合物时的焓变。

Hess’s law states that the total enthalpy change for a reaction is independent of the route taken. It allows us to calculate enthalpy changes that cannot be measured directly by combining known enthalpy changes. Enthalpy level diagrams and Born–Haber cycles are visual tools. Bond enthalpies can also be used to estimate ΔH for gas-phase reactions: ΔH ≈ Σ (bond enthalpies broken) − Σ (bond enthalpies formed). Mean bond enthalpies are average values over a range of compounds.

盖斯定律指出，一个反应的总焓变与所采取的路径无关。它使我们能够通过组合已知焓变，计算出无法直接测定的焓变。焓级图与玻恩-哈伯循环是可视化的工具。键焓也可用于估算气相反应的ΔH：ΔH ≈ Σ（断裂键的键焓）− Σ（形成键的键焓）。平均键焓是在一系列化合物中取的平均值。

ΔH = Σ ΔH_f^⦵(products) − Σ ΔH_f^⦵(reactants)

10. Introduction to Organic Chemistry: Alkanes, Alkenes and Halogenoalkanes | 有机化学导论：烷烃、烯烃与卤代烷

Organic chemistry is the chemistry of carbon compounds. Carbon forms four covalent bonds and can catenate to form chains and rings. Functional groups determine the chemical properties of organic molecules. The IUPAC system provides rules for systematic naming based on the longest carbon chain and the position of functional groups. Isomerism arises when molecules have the same molecular formula but different structures (structural isomers) or different arrangement in space (stereoisomers, e.g., E/Z isomers in alkenes).

有机化学是碳化合物的化学。碳可以形成四个共价键并能自相连结成链和环。官能团决定了有机分子的化学性质。IUPAC系统提供了基于最长碳链和官能团位置的系统命名规则。当分子具有相同的分子式但结构不同（结构异构体）或空间排列不同时（立体异构体，例如烯烃的E/Z异构），就会产生同分异构现象。

Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They undergo combustion (complete: CO₂ + H₂O; incomplete: CO + H₂O) and free-radical substitution with halogens in the presence of UV light. The mechanism involves initiation (Cl₂ → 2Cl•), propagation (Cl• + CH₄ → •CH₃ + HCl; •CH₃ + Cl₂ → CH₃Cl + Cl•) and termination steps. Alkenes contain a C=C double bond and are unsaturated. They undergo electrophilic addition reactions with hydrogen, halogens, hydrogen halides, and steam. The mechanism involves the attack of an electrophile on the electron-rich double bond, forming a carbocation intermediate. Markovnikov’s rule predicts the major product when adding unsymmetrical reagents.

烷烃是通式为CₙH₂ₙ₊₂的饱和碳氢化合物。它们能发生燃烧（完全燃烧：CO₂ + H₂O；不完全燃烧：CO + H₂O）以及在紫外光照射下与卤素发生的自由基取代反应。反应机理包括链引发（Cl₂ → 2Cl•）、链传递（Cl• + CH₄ → •CH₃ + HCl; •CH₃ + Cl₂ → CH₃Cl + Cl•）和链终止步骤。烯烃含有C=C双键，是不饱和烃。它们与氢气、卤素、卤化氢和水蒸气发生亲电加成反应。机理是亲电试剂进攻电子云丰富的双键，形成碳正离子中间体。与不对称试剂加成时，马氏规则可预测主要产物。

Halogenoalkanes contain a polar C–X bond. They undergo nucleophilic substitution reactions with hydroxide ions, cyanide ions and ammonia, as well as elimination reactions with hot ethanolic KOH to form alkenes. The rate of hydrolysis of halogenoalkanes depends on the carbon–halogen bond strength, decreasing in the order C–I > C–Br > C–Cl > C–F.

卤代烷含有极性的C–X键。它们能与氢氧根离子、氰根离子和氨发生亲核取代反应，也能在热乙醇KOH溶液中发生消除反应生成烯烃。卤代烷水解的速率取决于碳-卤键的强度，顺序为C–I > C–Br > C–Cl > C–F。

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CH01 Core Principles of Chemistry | 化学CH01核心原理