📚 Unit 803: Particle Model and States of Matter | 单元803：粒子模型与物态
Everything around us – from the air we breathe to the water we drink – is made of tiny particles. In Edexcel IGCSE Science, understanding the particle model is essential because it explains the properties of solids, liquids and gases, as well as how changes of state and phenomena like diffusion and gas pressure occur. This article covers all the key ideas you need, from the arrangement of particles to the Kelvin temperature scale and Boyle's law.
我们周围的一切——从呼吸的空气到饮用的水——都是由微小的粒子构成的。在爱德思IGCSE科学中，理解粒子模型至关重要，因为它能解释固体、液体和气体的性质，以及状态变化、扩散和气压等现象是如何发生的。本文涵盖了你需要掌握的所有关键概念，从粒子的排列方式到开尔文温标和波义耳定律。
1. The Building Blocks of Matter | 物质的构成基石
All substances are made up of very small particles – atoms, molecules or ions. These particles are in constant motion, and the way they are arranged and move determines whether the substance is a solid, a liquid or a gas. In a particle diagram, we represent them as tiny spheres. The spaces between the particles are much larger than the particles themselves, which explains why most substances can be compressed to some degree and why matter is mostly empty space.
所有物质都由极小的粒子组成——原子、分子或离子。这些粒子一直在不停地运动，而它们的排列和运动方式决定了该物质是固体、液体还是气体。在粒子示意图中，我们用微小的球体来表示它们。粒子之间的空隙比粒子本身大得多，这就解释了为什么大多数物质在一定程度上可被压缩，以及为什么物质大部分是空的。
2. Arrangement and Movement in the Three States | 三态中粒子的排列与运动
In a solid, particles are packed closely together in a fixed, regular pattern. They vibrate around fixed positions but do not move from place to place. This gives solids a definite shape and a fixed volume. In a liquid, particles are still close together but are arranged randomly; they can slide past one another, allowing liquids to flow and take the shape of their container while keeping a constant volume. In a gas, particles are far apart, arranged randomly and move rapidly in all directions. Gases have no fixed shape or volume and will completely fill any container.
在固体中，粒子紧密地堆积在一起，形成固定、规则的排列。它们在固定的位置上振动，但不会从一个位置移动到另一个位置。这赋予了固体确定的形状和固定的体积。在液体中，粒子仍然靠得很近，但排列不规则；它们可以相互滑动，使液体能够流动并呈现容器的形状，同时保持恒定的体积。在气体中，粒子相距很远，排列杂乱，并且向各个方向快速运动。气体没有固定的形状和体积，会完全充满任何容器。
- Solid: fixed shape, fixed volume, least energy / 固体：形状固定，体积固定，能量最低
- Liquid: no fixed shape, fixed volume, more energy / 液体：形状不固定，体积固定，能量较高
- Gas: no fixed shape, no fixed volume, most energy / 气体：形状不固定，体积不固定，能量最高
3. Comparative Properties in a Table | 用表格比较三态性质
| Property / 性质 | Solid / 固体 | Liquid / 液体 | Gas / 气体 |
|---|---|---|---|
| Particle arrangement / 粒子排列 | Regular, close / 规则紧密 | Random, close / 不规则紧密 | Random, far apart / 不规则稀疏 |
| Particle movement / 粒子运动 | Vibrate about fixed positions / 固定位置振动 | Slide past each other / 相互滑动 | Move fast in all directions / 向各方向快速运动 |
| Forces between particles / 粒子间作用力 | Strong / 强 | Weaker / 较弱 | Very weak / 非常弱 |
| Density / 密度 | Usually high / 通常高 | High, but often lower than solid / 高但常低于固体 | Very low / 非常低 |
| Compressibility / 可压缩性 | Very difficult / 非常难 | Slightly / 略微 | Easy / 容易 |
4. Changes of State | 物态变化
When a solid is heated, particles gain kinetic energy and vibrate more vigorously. At the melting point, the particles have enough energy to break out of their fixed positions, and the solid turns into a liquid. This process is called melting. Further heating gives particles even more energy; at the boiling point, liquid particles break free from each other completely to form a gas – this is boiling or evaporation. The reverse processes are freezing (liquid to solid) and condensation (gas to liquid). Sublimation is the change directly from solid to gas, as seen with dry ice (solid carbon dioxide).
当固体受热时，粒子获得动能，振动得更剧烈。在熔点时，粒子拥有了足够的能量，能够摆脱固定的位置，固体就变成了液体。这个过程叫做熔化。继续加热使粒子的能量进一步提高；在沸点，液体粒子彼此完全挣脱，形成气体——这就是沸腾或蒸发。相反的过程是凝固（液体变固体）和冷凝（气体变液体）。升华是直接从固体变成气体的过程，例如干冰（固体二氧化碳）所表现的那样。
Melting: solid → liquid / 熔化：固体 → 液体
Boiling: liquid → gas / 沸腾：液体 → 气体
Condensing: gas → liquid / 冷凝：气体 → 液体
Freezing: liquid → solid / 凝固：液体 → 固体
Sublimation: solid → gas / 升华：固体 → 气体
5. Energy, Temperature, and Kinetic Theory | 能量、温度与分子动理论
The temperature of a substance is a measure of the average kinetic energy of its particles. Heating a substance increases the kinetic energy of its particles, making them move faster. During a change of state, however, the temperature remains constant even while heat is being supplied. This is because the energy is used to overcome the attractive forces between particles rather than to raise their kinetic energy. This hidden energy is called latent heat. For example, the specific latent heat of fusion for ice is 334 J/g.
物质的温度是其粒子平均动能的量度。加热物质会增加粒子的动能，使它们运动得更快。然而，在状态变化过程中，即使持续供热，温度也保持恒定。这是因为能量被用来克服粒子之间的吸引力，而不是用来增加粒子的动能。这部分隐藏的能量称为潜热。例如，冰的熔化比潜热为334焦耳/克。
6. Brownian Motion – Evidence for Particles | 布朗运动——粒子存在的证据
Brownian motion is the random, jerky movement of tiny particles suspended in a fluid (liquid or gas). It was first observed by the botanist Robert Brown while looking at pollen grains in water. This motion is caused by the many smaller, invisible particles of the fluid bombarding the larger visible particles from all sides. Brownian motion provides direct evidence for the kinetic particle model and shows that particles in fluids are in constant, random motion.
布朗运动是悬浮在流体（液体或气体）中的微小粒子所做的不规则、急动的运动。植物学家罗伯特·布朗在观察水中的花粉粒时首次发现了这种现象。这一运动是由流体中无数更小的、看不见的粒子从各个方向撞击较大的可见粒子所造成的。布朗运动为分子动理论提供了直接证据，并表明流体中的粒子处于持续不断的随机运动之中。
7. Diffusion – Particles on the Move | 扩散——运动中的粒子
Diffusion is the net movement of particles from a region of high concentration to a region of low concentration, due to the random motion of particles. It is fastest in gases, slower in liquids and exceptionally slow in solids. For example, when a perfume bottle is opened at one corner of a room, the scent gradually spreads until it can be smelled everywhere. Diffusion is speeded up by higher temperatures because particles have greater kinetic energy and move faster. The relative molecular mass of the gas also affects the rate of diffusion – lighter gases diffuse more quickly than heavier ones.
扩散是粒子由于随机运动而从高浓度区域向低浓度区域净移动的过程。扩散在气体中最快，在液体中较慢，在固体中则极慢。例如，当在房间一角打开一瓶香水时，香气逐渐扩散，直至整个房间都能闻到。较高的温度会加快扩散速度，因为粒子的动能更大，运动更快。气体的相对分子质量也会影响扩散速率——较轻的气体比较重的气体扩散得更快。
8. Gas Pressure Explained by Particles | 用粒子解释气体压强
Gas pressure is caused by the collisions of gas particles with the walls of a container. Each collision exerts a tiny force; the total force per unit area is the pressure. If the temperature of a gas is increased (at constant volume), particles move faster and hit the walls more frequently and with greater force, so the pressure rises. Conversely, if the volume of a container is increased (at constant temperature), particles have to travel further to hit the walls, leading to fewer collisions per second and a decrease in pressure. These relationships are summarised by the kinetic theory of gases.
气体压强是由气体粒子与容器壁碰撞引起的。每次碰撞都会产生一个微小的力；单位面积上的总力就是压强。如果在体积不变的条件下升高气体的温度，粒子运动得更快，会更频繁、更有力地撞击器壁，因此压强会升高。相反，如果在温度不变的条件下增大容器的体积，粒子需要移动更远的距离才能撞到器壁，导致每秒钟的碰撞次数减少，压强降低。气体分子动理论概括了这些关系。
9. Kelvin Temperature Scale and Absolute Zero | 开尔文温标与绝对零度
e average kinetic energy of particles. Zero kelvin (0 K) is called absolute zero, which is – lsius to Kelvin, simply add 273: T (K) = θ (°C) + 273. A rise of 1°C equals a rise of 1 K.
在开尔文温标上，温度与粒子的平均动能成正比。零开尔文（0 K）被称为绝对零度，即 –273°C。在绝对零度时，粒子的动能达到可能的最低值，理论上所有运动都会停止。开尔文温标在科学上至关重要，因为它没有负数，并且与能量之间的线性关系是真实的。从摄氏度转换为开尔文，只需加上273：T (K) = θ (°C) + 273。1°C的升高等于1 K的升高。
Absolute zero = 0 K = –273°C / 绝对零度 = 0 K = –273°C
10. Boyle's Law – Pressure and Volume | 波义耳定律——压强与体积
f gas at constant temperature, pressure is inversely proportional to volume. This is Boyle' you squeeze a gas into a smaller volume, the particles hit the walls more often because they have less distance to travel, so the pressure goes up. When the volume is doubled, the pressure halves, provided the temperature stays the same. This relationship can be demonstrated with a syringe connected to a pressure gauge.
对于一定质量的气体，在温度不变的条件下，压强与体积成反比。这就是波义耳定律，通常写作 p₁V₁ = p₂V₂。如果将气体压缩到更小的体积中，粒子运动距离变短，因此它们会更频繁地撞击器壁，使压强升高。当体积增大一倍时，压强就会减半，前提是温度保持不变。这一关系可以用连接着压力计的注射器来演示。
p × V = constant (at constant temperature) / p × V = 常数（恒温下）
11. Evaporation vs Boiling | 蒸发与沸腾的区别
Boiling occurs throughout a liquid at a specific temperature called the boiling point. Evaporation, on the other hand, happens only at the surface of a liquid and can take place at any temperature. During evaporation, the fastest-moving particles near the surface escape, so the average kinetic energy of the remaining liquid drops – this is why evaporation causes cooling. Factors that increase the rate of evaporation include higher temperature, larger surface area and the presence of a draught (moving air).
沸腾发生在一个特定的温度——沸点下，并且在整个液体内部进行。而蒸发只发生在液体表面，可以在任何温度下进行。在蒸发过程中，液面附近运动最快的粒子会逃逸出去，因此剩下液体的平均动能下降——这就是蒸发能导致冷却的原因。提高蒸发速率的因素包括更高的温度、更大的表面积以及气流（空气流动）的存在。
12. Applying the Particle Model in IGCSE Exams | 粒子模型在IGCSE考试中的应用
In Edexcel IGCSE Science papers, you will often be asked to explain everyday observations using the particle model. For instance, why does a balloon inflate when you pump air into it? More particles inside mean more collisions per second on the inner walls, increasing pressure and causing the balloon to expand. Why does a metal lid become easier to open after running it under hot water? The metal expands slightly when heated; particle vibrations increase and the lid loosens. Always link macroscopic properties to the microscopic behaviour of particles when constructing your answers.
在爱德思IGCSE科学的试卷中，你常常会被要求用粒子模型解释日常现象。例如，为什么给气球打气时它会膨胀？因为内部粒子增多，每秒钟对气壁的碰撞次数增加，使压强增大，导致气球膨胀。为什么金属盖子用热水冲淋后更容易拧开？金属受热轻微膨胀；粒子的振动加剧，盖子便松动了。在组织答案时，一定要把宏观性质与粒子的微观行为联系起来。
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