📚 Elements and Atoms | 元素与原子
In A-level Chemistry, the concepts of elements and atoms form the foundation of all chemical understanding. An element is a pure substance made of only one type of atom, while an atom is the smallest unit of an element that retains its chemical properties. This article examines atomic structure, isotopes, relative atomic mass, mass spectrometry, electron configurations, and periodic trends.
在A-level化学中，元素与原子的概念是所有化学理解的基础。元素是由同一种原子组成的纯净物，而原子是保留元素化学性质的最小单元。本文探讨原子结构、同位素、相对原子质量、质谱、电子排布和周期趋势。
1. Elements and Atoms: Core Definitions | 元素与原子：核心定义
An element is a substance that cannot be broken down into simpler substances by chemical means. Each element consists of atoms with the same number of protons in the nucleus, known as the atomic number (Z).
元素是无法通过化学方法分解为更简单物质的物质。每种元素由原子核中质子数相同的原子组成，这个数目称为原子序数（Z）。
An atom is the smallest particle of an element that can take part in a chemical reaction. Atoms are electrically neutral because the number of protons equals the number of electrons.
原子是元素能参与化学反应的最小粒子。原子呈电中性，因为质子数等于电子数。
2. Subatomic Particles | 亚原子粒子
Atoms consist of three main subatomic particles: protons, neutrons, and electrons. Protons carry a positive charge (+1) and have a relative mass of 1. Neutrons are neutral (0) with a relative mass of 1. Electrons carry a negative charge (−1) and have a negligible mass of 1/1836 relative to a proton.
原子由三种主要亚原子粒子组成：质子、中子和电子。质子带正电荷（+1），相对质量为1。中子不带电（0），相对质量为1。电子带负电荷（−1），质量极小，约为质子的1/1836。
Protons and neutrons are located in the central nucleus, while electrons occupy regions of space called orbitals surrounding the nucleus. The nucleus is extremely dense and contains nearly all the mass of the atom.
质子和中子位于中心的原子核内，而电子占据原子核外称为轨道的空间区域。原子核密度极高，几乎包含原子的全部质量。
3. Atomic Number and Mass Number | 原子序数与质量数
The atomic number (Z) is the number of protons in the nucleus and defines the identity of the element. In a neutral atom, Z also equals the number of electrons.
原子序数（Z）是原子核中的质子数，决定了元素的种类。在中性原子中，Z也等于电子数。
The mass number (A) is the total number of protons and neutrons in the nucleus. It is an integer close to the relative atomic mass but not identical for elements with multiple isotopes.
质量数（A）是原子核中质子和中子的总数。它是一个整数，接近相对原子质量，但对于存在多种同位素的元素并不相同。
Nuclide notation is written as AZX, for example 126C for carbon-12, where 12 is the mass number and 6 is the atomic number.
核素符号写作 AZX，例如 126C 表示碳-12，其中12是质量数，6是原子序数。
4. Isotopes | 同位素
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties because electron arrangements are the same, but their physical properties such as mass and density differ.
同位素是同一元素中质子数相同但中子数不同的原子。由于电子排布相同，它们具有相同的化学性质，但质量和密度等物理性质不同。
For example, carbon has three naturally occurring isotopes: carbon-12 (12C), carbon-13 (13C), and carbon-14 (14C). All have 6 protons, but 6, 7, and 8 neutrons respectively.
例如，碳有三种天然同位素：碳-12（12C）、碳-13（13C）和碳-14（14C）。三者都有6个质子，但分别有6、7、8个中子。
Some isotopes are radioactive and decay over time, such as 14C used in radiocarbon dating. Stable isotopes like 12C and 13C do not undergo radioactive decay.
一些同位素具有放射性并会随时间衰变，例如用于放射性碳定年的14C。像12C和13C这样的稳定同位素不会发生放射性衰变。
5. Relative Atomic Mass and Relative Isotopic Mass | 相对原子质量与相对同位素质量
Relative isotopic mass is the mass of one atom of an isotope compared to 1/12 the mass of a carbon-12 atom. Since carbon-12 is assigned a mass of exactly 12 u, relative isotopic masses are close to the mass number.
相对同位素质量是一个同位素原子的质量与碳-12原子质量的1/12之比。由于碳-12被指定为恰好12 u，相对同位素质量接近质量数。
Relative atomic mass (Aᵣ) is the weighted average mass of an element's isotopes relative to 1/12 the mass of carbon-12. It accounts for the natural abundance of each isotope.
相对原子质量（Aᵣ）是元素各同位素相对于碳-12质量的1/12的加权平均质量。它考虑了每种同位素的天然丰度。
Aᵣ = Σ (isotopic mass × % abundance) / 100
For example, chlorine has two main isotopes: 35Cl (75%) and 37Cl (25%). Aᵣ = (35 × 75 + 37 × 25) / 100 = 35.5.
例如，氯有两种主要同位素：35Cl（75%）和37Cl（25%）。Aᵣ =（35 × 75 + 37 × 25）/ 100 = 35.5。
6. Mass Spectrometry | 质谱法
A mass spectrometer is used to determine the relative atomic mass of an element and the abundance of its isotopes. The sample is vaporised, ionised, accelerated, deflected by a magnetic field, and detected.
质谱仪用于测定元素的相对原子质量及其同位素丰度。样品经过气化、电离、加速、在磁场中偏转和检测。
The key stages are: ionisation (electron impact or electrospray), acceleration through an electric field, deflection by a magnetic field where lighter and more highly charged ions deflect more, and detection producing a mass spectrum.
关键步骤是：电离（电子轰击或电喷雾）、通过电场加速、在磁场中偏转（较轻和带电荷更多的离子偏转更大）以及检测产生质谱图。
In the mass spectrum, each peak corresponds to an isotope. The m/z value gives the mass-to-charge ratio, and peak heights indicate relative abundance.
在质谱图中，每个峰对应一种同位素。m/z值给出质荷比，峰高表示相对丰度。
Relative atomic mass is calculated from the mass spectrum by multiplying each m/z value by its relative abundance, summing these products, and dividing by the total relative abundance.
相对原子质量由质谱图计算，将每个m/z值乘以其相对丰度，求和后除以总相对丰度。
7. Electron Arrangement and Orbitals | 电子排布与轨道
abelled s, p, d, and f. Each subshell has a fixed number of orbitals: s has 1, p has 3, d has 5, f has 7. Each orbital holds a maximum of two electrons with opposite spins.
电子占据原子核外的电子层和亚层。主层（n = 1, 2, 3, ...）包含标为s、p、d、f的亚层。每个亚层有固定数目的轨道：s有1个，p有3个，d有5个，f有7个。每个轨道最多容纳两个自旋相反的电子。
The order of filling orbitals follows the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc. Hund's rule states that electrons fill degenerate orbitals singly before pairing.
轨道填充顺序遵循构造原理：1s、2s、2p、3s、3p、4s、3d、4p等。洪特规则指出，电子在简并轨道中先单独填充再配对。
s² 2s² 2p⁶ 3s¹. For ions, electrons are added or removed from the highest energy subshell.
电子排布用上标表示电子数，例如钠（Z=11）的排布为1s² 2s² 2p⁶ 3s¹。对于离子，电子从最高能级亚层中添加或移除。
8. Ionisation Energy | 电离能
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 1+ ions. It is an endothermic process.
第一电离能是从一摩尔气态原子中移除一摩尔电子形成一摩尔气态1+离子所需的能量。这是一个吸热过程。
Trends in first ionisation energy across a period show a general increase because nuclear charge increases while shielding remains similar, pulling outer electrons more strongly. Down a group, ionisation energy decreases because outer electrons are further from the nucleus and experience more shielding.
第一电离能在同一周期中总体呈上升趋势，因为核电荷增加而屏蔽效应相似，对外层电子吸引更强。沿族向下，电离能降低，因为外层电子离核更远并受到更多屏蔽。
Dips in the trend, such as between groups 2 and 3, arise from electron repulsion in a new subshell of higher energy. Dips between groups 5 and 6 arise from spin-pair repulsion in an orbital.
趋势中的下降，例如第2族与第3族之间，是由于电子进入能量更高的新亚层产生排斥。第5族与第6族之间的下降是由于轨道中电子自旋配对排斥。
9. The Periodic Table and Element Classification | 元素周期表与元素分类
The periodic table arranges elements in order of increasing atomic number. Elements with similar chemical properties fall into the same group (vertical column) because they have the same number of outer-shell electrons.
元素周期表按原子序数递增的顺序排列元素。具有相似化学性质的元素位于同一族（竖列），因为它们具有相同的外层电子数。
Periods (horizontal rows) correspond to the filling of successive main electron shells. The block of an element (s, p, d, f) is determined by the subshell in which the highest-energy electrons reside.
周期（横行）对应着逐级填充的主电子层。元素的区（s、p、d、f）由最高能级电子所在的亚层决定。
Metals, non-metals, and metalloids are classified based on properties such as conductivity, ionisation energy, and electronegativity. Metals tend to lose electrons to form cations, while non-metals gain electrons to form anions.
金属、非金属和类金属根据导电性、电离能和电负性等性质进行分类。金属倾向于失去电子形成阳离子，而非金属倾向于获得电子形成阴离子。
10. Elements and Atoms in Stoichiometry | 化学计量中的元素与原子
constant (6.02 × 10²³) of atoms and has a mass equal to its relative atomic mass in grams.
摩尔概念将元素的质量与原子数联系起来。一摩尔任何元素包含阿伏伽德罗常数（6.02 × 10²³）个原子，其质量以克为单位等于其相对原子质量。
ount in moles, m is mass in grams, and M is molar mass in g mol⁻¹, calculations can be performed.
例如，12克碳-12恰好含有6.02 × 10²³个碳原子。使用公式 n = m / M（n为物质的量，m为质量，M为摩尔质量）可进行计算。
Empirical and molecular formulae are derived from the ratios of atoms in a compound. Combustion analysis and mass spectrometry help determine these formulae.
经验式和分子式由化合物中原子的比例推导得出。燃烧分析和质谱法有助于确定这些化学式。
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