📚 Particle Theory Worksheet: Solids, Liquids and Gases | 粒子理论练习题：固体、液体和气体
This worksheet-style guide covers the particle theory of matter for KS3 CIE science. Read each section carefully, then test yourself with the quick-check questions at the end. The particle model is a powerful idea: it explains the behaviour of solids, liquids and gases using only tiny moving particles.
本练习式指南涵盖 KS3 CIE 科学中物质的粒子理论。请仔细阅读每个部分，然后用文末的快速检测题自测。粒子模型是一个强大的概念：它只用微小运动粒子就能解释固体、液体和气体的行为。
1. The Particle Model of Matter | 物质的粒子模型
All matter is made of very small particles. These particles can be atoms, molecules or ions, depending on the substance. In the particle model, we imagine particles as tiny spheres that are always moving.
所有物质都由非常小的粒子组成。这些粒子可以是原子、分子或离子，具体取决于物质种类。在粒子模型中，我们把粒子想象成总是在运动的微小圆球。
The properties of a material depend on how these particles are arranged and how strongly they attract one another. The main states of matter are solid, liquid and gas.
材料的性质取决于这些粒子如何排列以及它们之间的吸引力有多强。物质的主要状态是固态、液态和气态。
The particle model is a scientific model, so it simplifies reality but still makes useful predictions.
粒子模型是一种科学模型，因此它简化了现实，但仍能做出有用的预测。
2. Solids: Fixed Shape and Volume | 固体：形状和体积固定
In a solid, particles are packed closely together in a regular, repeating pattern. They are held tightly by strong forces of attraction, so they can only vibrate around fixed positions.
在固体中，粒子紧密排列成规则、重复的结构。它们被强大的吸引力紧紧束缚，因此只能在固定位置附近振动。
Because the particles cannot move past one another, solids have a fixed shape and a fixed volume. They cannot be compressed because there is very little space between particles.
由于粒子无法彼此滑动，固体具有固定的形状和固定的体积。固体不能被压缩，因为粒子之间的空间非常小。
3. Liquids: Fixed Volume, Changing Shape | 液体：体积固定，形状可变
In a liquid, particles are still close together but are arranged irregularly. They have enough energy to slide past one another, which allows a liquid to flow and take the shape of its container.
在液体中，粒子仍然彼此靠近，但排列不规则。它们有足够的能量相互滑动，因此液体能够流动并呈现容器的形状。
Liquids have a fixed volume because the particles remain roughly the same distance apart. They are almost impossible to compress because there is little free space between particles.
液体具有固定的体积，因为粒子之间的距离大致保持不变。液体几乎不能压缩，因为粒子之间几乎没有自由空间。
4. Gases: No Fixed Shape or Volume | 气体：没有固定形状或体积
In a gas, particles are very far apart and move rapidly in all directions. The forces of attraction between gas particles are very weak, so they spread out to fill the whole container.
在气体中，粒子相距很远，并朝各个方向快速运动。气体粒子之间的吸引力非常弱，因此它们会扩散并充满整个容器。
Gases have no fixed shape and no fixed volume. They can be compressed easily because there is a lot of space between particles, which can be reduced under pressure.
气体没有固定的形状和体积。气体容易被压缩，因为粒子之间有大量空间，在压力下这些空间可以减小。
5. Kinetic Energy and Temperature | 动能与温度
Temperature is a measure of the average kinetic energy of particles. The faster the particles move, the higher the temperature of the substance.
温度是粒子平均动能的量度。粒子运动越快，物质的温度就越高。
Heating a substance transfers energy to its particles, making them move faster. Cooling removes energy, so the particles slow down.
加热物质会将能量传递给其粒子，使它们运动得更快。冷却则会带走能量，使粒子运动减慢。
Eₖ ∝ T
At absolute zero (0 K or -273 °C), particles have the minimum possible energy and almost stop moving.
在绝对零度（0 K 或 -273 °C）时，粒子具有尽可能低的能量，几乎停止运动。
6. Changes of State | 状态变化
Changing state involves adding or removing energy. Melting, boiling and sublimation need energy input; freezing, condensation and deposition release energy.
状态变化涉及能量的输入或输出。熔化、沸腾和升华需要输入能量；凝固、凝结和凝华则释放能量。
During a change of state, the temperature stays constant even though energy is still being transferred. This energy is used to break attractive forces between particles rather than to raise the temperature.
在状态变化过程中，即使能量仍在传递，温度也保持不变。这些能量用于克服粒子之间的吸引力，而不是升高温度。
solid ⇌ liquid ⇌ gas
Melting point is the temperature at which a solid becomes a liquid. Boiling point is the temperature at which a liquid becomes a gas throughout the liquid.
熔点是固体变为液体的温度。沸点是液体内部到处都变为气体的温度。
7. Expansion and Contraction | 热胀冷缩
When a substance is heated, its particles gain kinetic energy and move further apart. This makes the substance expand. Cooling makes particles move less and move closer together, so the substance contracts.
物质受热时，粒子获得动能并彼此远离，因此物质膨胀。冷却时粒子运动减少并彼此靠近，因此物质收缩。
Expansion is most noticeable in gases, less in liquids and very small in solids. Bridges and railway tracks have expansion gaps to allow for expansion in hot weather.
膨胀在气体中最明显，液体次之，固体中非常微小。桥梁和铁轨留有伸缩缝，以应对高温天气中的膨胀。
Water is an unusual exception: ice is less dense than liquid water, so ice floats. This happens because water particles form an open structure when they freeze.
水是一个特殊例外：冰的密度小于液态水，因此冰会漂浮。这是因为水结冰时粒子形成开放结构。
8. Diffusion | 扩散
Diffusion is the movement of particles from a region of high concentration to a region of low concentration. It happens because particles move randomly and spread out.
扩散是粒子从高浓度区域向低浓度区域运动的过程。它之所以发生，是因为粒子随机运动并逐渐分散。
Diffusion is fastest in gases, slower in liquids and extremely slow in solids. For example, the smell of perfume spreads quickly across a room because gas particles move fast and collide often.
扩散在气体中最快，液体中较慢，固体中极其缓慢。例如，香水的香味能迅速在房间中扩散，因为气体粒子运动快且频繁碰撞。
Heating speeds up diffusion because particles gain more kinetic energy and move faster.
加热会加速扩散，因为粒子获得更多动能，运动更快。
9. Gas Pressure | 气体压强
Gas pressure is caused by gas particles colliding with the walls of their container. Each collision exerts a small force; many collisions produce a steady pressure.
气体压强是由气体粒子撞击容器壁引起的。每次碰撞都施加一个微小的力；大量碰撞就产生稳定的压强。
If the temperature of a gas increases while the volume stays the same, the particles move faster and collide more often and harder, so the pressure increases.
如果气体温度升高而体积保持不变，粒子运动更快，碰撞更频繁、更有力，因此压强增大。
If the volume of a gas is decreased, the particles hit the walls more often, so the pressure increases. This is why squeezing a sealed syringe feels harder.
如果气体体积减小，粒子撞击器壁更频繁，因此压强增大。这就是挤压密封注射器时会感觉更费力的原因。
10. Density and the Particle Model | 密度与粒子模型
Density is the mass of a substance divided by its volume. The particle model explains density: the closer the particles, the greater the mass in a given space.
密度是物质的质量除以其体积。粒子模型可解释密度：粒子越紧密，给定空间内的质量就越大。
ρ = m ÷ V
Solids are usually denser than liquids, and liquids are usually denser than gases, because particles are packed more tightly in solids and liquids.
固体通常比液体密度大，液体通常比气体密度大，因为固体和液体中的粒子排列更紧密。
Ice floats on water because solid water is less dense than liquid water. This is unusual
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