Fundamental Concepts of Atoms and Molecules | 原子与分子基本概念梳理

📚 Fundamental Concepts of Atoms and Molecules | 原子与分子基本概念梳理

Understanding the basic building blocks of matter—atoms and molecules—is essential for studying chemistry. These fundamental concepts explain the composition, structure, and behavior of all substances.

理解物质的基本构建单元——原子和分子，对于学习化学至关重要。这些基本概念解释了所有物质的组成、结构和行为。

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1. What is an Atom? | 什么是原子？

An atom is the smallest unit of an element that retains the chemical properties of that element. It consists of a dense nucleus surrounded by a cloud of electrons.

原子是元素的最小单元，它保持了该元素的化学性质。它由一个致密的原子核和围绕它的电子云组成。

Atoms are extremely small; their diameters are typically around 10⁻¹⁰ meters. They cannot be seen with ordinary light microscopes, but can be imaged using special techniques like scanning tunneling microscopy.

原子极其微小；它们的直径通常在 10⁻¹⁰ 米左右。它们无法用普通光学显微镜看到，但可以使用扫描隧道显微镜等特殊技术进行成像。

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2. Early Atomic Theory: Dalton’s Model | 早期原子理论：道尔顿模型

In 1808, John Dalton proposed his atomic theory, stating that all matter is made of indivisible atoms, atoms of the same element are identical, compounds form by combining atoms of different elements, and chemical reactions involve rearrangement of atoms.

1808 年，约翰·道尔顿提出了他的原子论，声称所有物质都由不可分割的原子组成，同一元素的原子完全相同，化合物由不同元素的原子结合形成，化学反应涉及原子的重新排列。

Although some of Dalton’s ideas have been modified (atoms can be divided into subatomic particles, and isotopes exist), his theory laid the foundation for modern chemistry.

尽管道尔顿的某些观点已经被修正（原子可再分为亚原子粒子，并且存在同位素），但他的理论为现代化学奠定了基础。

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3. Subatomic Particles | 亚原子粒子

Atoms are composed of three main subatomic particles: protons (positively charged), neutrons (neutral), and electrons (negatively charged). Protons and neutrons make up the nucleus, while electrons orbit around it.

原子由三种主要的亚原子粒子组成：质子（带正电）、中子（不带电）和电子（带负电）。质子和中子组成原子核，电子则围绕原子核运行。

The relative masses of these particles are: proton ≈ 1 atomic mass unit (u), neutron ≈ 1 u, and electron ≈ 1/1836 u. The electron’s mass is negligible for most calculations. The charges are: proton +1, neutron 0, electron –1, in units of elementary charge.

这些粒子的相对质量为：质子 ≈ 1 原子质量单位 (u)，中子 ≈ 1 u，电子 ≈ 1/1836 u。在大多数计算中，电子的质量可以忽略不计。电荷以基本电荷为单位：质子 +1，中子 0，电子 –1。

Understanding these particles is key to explaining why atoms are neutral and how they can become charged.

理解这些粒子是解释原子为何呈电中性以及如何变成带电粒子的关键。

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4. Structure of the Atom and Atomic Number | 原子结构及原子序数

The nucleus is tiny compared to the overall volume of the atom, yet it contains almost all the mass. The number of protons in the nucleus is called the atomic number (Z), which uniquely defines an element.

与原子整体体积相比，原子核极小，但却包含了几乎所有的质量。原子核中质子的数量称为原子序数 (Z)，它唯一地定义了一种元素。

For a neutral atom, the number of protons equals the number of electrons, so the net charge is zero. The mass number (A) is the total number of protons and neutrons in the nucleus.

对于中性原子，质子数等于电子数，因此净电荷为零。质量数 (A) 是原子核中质子与中子的总数。

Neutrons = Mass number (A) – Atomic number (Z)

中子数 = 质量数 (A) – 原子序数 (Z)

This simple relationship allows us to determine the number of neutrons in any atom.

这一简单关系让我们可以确定任何原子中的中子数。

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5. Isotopes | 同位素

Atoms of the same element always have the same number of protons, but they can have different numbers of neutrons. Such varieties are called isotopes.

同一元素的原子总是具有相同数量的质子，但它们的中子数可以不同。这些变种称为同位素。

For example, carbon has three naturally occurring isotopes, as shown in the table below. They all have 6 protons (thus atomic number 6), but differ in the number of neutrons and mass number.

例如，碳有三种天然存在的同位素，如下表所示。它们都有 6 个质子（因此原子序数为 6），但中子数和质量数不同。

Isotope	Protons	Neutrons	Mass Number (A)
Carbon-12 (¹²C)	6	6	12
Carbon-13 (¹³C)	6	7	13
Carbon-14 (¹⁴C)	6	8	14

Isotopes exhibit identical chemical properties because chemical behavior is determined by the electron arrangement, which depends only on the number of protons (and thus electrons in a neutral atom). Their physical properties and nuclear stability may differ.

同位素表现出相同的化学性质，因为化学行为由电子排布决定，而电子排布仅取决于质子数（以及中性原子中的电子数）。它们的物理性质和核稳定性可能不同。

Many elements consist of a mixture of isotopes. The relative atomic mass of an element takes the abundance of each isotope into account.

许多元素是同位素的混合物。元素的相对原子质量考虑了每种同位素的丰度。

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6. Ions: Charged Particles | 离子：带电粒子

When an atom gains or loses electrons, it becomes an ion. If it loses one or more electrons, it becomes a positively charged cation (e.g., Na⁺, Ca²⁺). If it gains electrons, it becomes a negatively charged anion (e.g., Cl⁻, O²⁻).

当原子获得或失去电子时，它就变成离子。如果失去一个或多个电子，它就变成带正电的阳离子（例如 Na⁺, Ca²⁺）。如果得到电子，就变成带负电的阴离子（例如 Cl⁻, O²⁻）。

The charge of an ion is written as a superscript: for a single charge, use + or –; for multiple charges, use the number followed by the sign, e.g., Mg²⁺, N³⁻. The number of protons remains unchanged, so the identity of the element does not change.

离子的电荷写成上标形式：单电荷用 + 或 –；多个电荷则用数字后跟符号，例如 Mg²⁺, N³⁻。质子数保持不变，因此元素的身份不变。

Ions play a crucial role in forming ionic compounds,

Published by TutorHao | Chemistry Revision Series | aleveler.com

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