Particle Model of Matter and States of Matter | 物质粒子模型与物质状态

📚 Particle Model of Matter and States of Matter | 物质粒子模型与物质状态

The particle model of matter is one of the most powerful tools in physics. It treats every material as a collection of tiny, discrete particles, and it can explain why substances exist as solids, liquids or gases. Understanding this model and how particles behave in each state is essential for describing phase changes, gas pressure and thermal energy.

物质粒子模型是物理学中最有力的工具之一。它将一切物质视为大量微小离散粒子的集合，并用它解释物质为何以固态、液态或气态存在。理解这一模型以及粒子在各状态中的行为，是描述相变、气体压强和热能的必要条件。

1. Fundamentals of the Particle Model | 粒子模型基础

The particle model makes five basic assumptions about matter: all matter is made of tiny particles called atoms, molecules or ions; these particles are always in motion; there is empty space between them; forces act between neighbouring particles; and temperature is a measure of the average kinetic energy of the particles.

粒子模型对物质作出五项基本假设：所有物质都由称为原子、分子或离子的微小粒子构成；这些粒子始终在运动；粒子之间存在空隙；相邻粒子间存在相互作用力；温度是粒子平均动能的量度。

• The diameter of a typical atom or molecule is about 10⁻¹⁰ m. In solids and liquids, the particles nearly touch one another, whereas in a gas the spacing is roughly ten times larger.
• 典型原子或分子的直径约为10⁻¹⁰ m。在固体和液体中，粒子几乎彼此相接；而在气体中，粒子间距约为前者的十倍。
• The forces between particles are attractive at moderate separations but become strongly repulsive when the particles are squeezed too close together. These forces are responsible for the strength of solids and the surface tension of liquids.
• 粒子间力在一定距离上表现为引力，但当粒子被压得过近时则表现为强斥力。正是这些力使固体具有强度、液体具有表面张力。
• When a substance is heated, its particles absorb energy. Their average kinetic energy increases, so the temperature rises; if the energy is large enough, the arrangement of particles breaks down and a phase change occurs.
• 当物质被加热时，粒子吸收能量。它们的平均动能增大，温度随之升高；如果能量足够大，粒子的排列被破坏，于是发生相变。

2. Solids | 固态

In a solid, particles are packed closely together in a regular, repeating lattice structure. Each particle vibrates about a fixed position, but it does not travel from place to place. The strong interparticle forces lock the particles into place, giving solids their rigid shape and fixed volume.

在固体中，粒子紧密堆积成规则、重复的晶格结构。每个粒子都在固定位置附近振动，但不能从一个位置移动到另一个位置。强大的粒子间力将粒子锁定在原位，使固体具有固定的形状和体积。

• Particles in a solid vibrate at very high frequency, typically around 10¹³ Hz, but their average position remains unchanged.
• 固体中粒子的振动频率很高，通常约为10¹³ Hz，但它们的平均位置保持不变。
• Because the particles are so close together, solids are almost incompressible and have high density. The regular lattice also explains why many crystals have flat faces and sharp edges.
• 由于粒子排列非常紧密，固体几乎不可压缩并且密度很大。规则的晶格也解释了为什么许多晶体具有平面和尖锐的棱边。
• When the temperature rises, the amplitude of vibration increases. At the melting point, the vibrations become vigorous enough to break the lattice apart.
• 当温度升高时，粒子振动的幅度增大。在熔点时，振动变得足够剧烈，使晶格分裂。

3. Liquids | 液态

In a liquid, particles remain close together but are no longer locked into a fixed lattice. They can slide past one another and may roll over each other, because the forces between them are weaker than in a solid. This is why a liquid pours and takes the shape of its container.

在液体中，粒子仍然紧密靠近，但不再被锁定在固定的晶格中。由于粒子间力比固体弱，它们可以相互滑动，也能彼此翻滚。这就是液体能够流动并随容器改变形状的原因。

• Liquid particles are in constant motion; they vibrate, slide and collide with their neighbours. There is a short-range order, so small clusters of particles form and break apart constantly.
• 液体粒子不断运动：它们振动、滑动并与邻近粒子碰撞。液体中存在短程有序，因而会不断形成和拆散小团粒子簇。
• Liquids have a fixed volume because the particles remain in close contact, but they have no fixed shape because the particles are free to move relative to one another.
• 液体具有固定体积，因为粒子仍保持紧密接触；但液体没有固定形状，因为粒子可以相对移动。
• Diffusion in a liquid is much slower than in a gas, though it still occurs. For example, a drop of ink spreads through water gradually as dye molecules collide and move randomly.
• 液体中的扩散远比气体慢，但仍然会发生。例如，一滴墨水在水中的扩散，就是染料分子碰撞并随机移动的结果。

4. Gases | 气态

In a gas, particles are far apart and move freely at high speeds in straight lines until they collide with one another or with the walls of a container. The interparticle forces are so weak that they can be ignored in most simple models. Because the particles are widely separated, gases have low density and are highly compressible.

在气体中，粒子相距很远，以高速沿直线自由运动，直到彼此碰撞或与容器壁碰撞。粒子间力非常弱，在大多数简单模型中可忽略不计。由于粒子间隔很大，气体密度低且高度可压缩。

• At room temperature and standard pressure, gas molecules travel at typical speeds of about 500 m/s. Between collisions, they move in straight lines.
• 在室温常压下，气体分子的典型运动速度约为500 m/s。在两次碰撞之间，它们沿直线运动。
• A gas always expands to fill its container completely. It has no fixed shape and no fixed volume, and its pressure arises from the impacts of particles on the container walls.
• 气体总是完全膨胀以充满整个容器。它没有固定的形状和体积，其对器壁的压强来自粒子的撞击。
• When a gas is compressed, the particles are forced closer together, so the number of collisions per second with the walls increases; this raises the pressure.
• 当气体被压缩时，粒子被迫靠拢，每秒与器壁碰撞的次数增加，从而使压强增大。

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5. Comparing the Three States | 三种状态的对比

The properties of solids, liquids and gases can be summarised in a compact table. In an exam, you may be asked to compare the particle spacing, motion and energy in two states, or to identify which state is being described from a diagram.

固体、液体和气体的性质可以用一张简表概括。在考试中，你可能会被要求比较两种状态的粒子间距、运动和能量，或者根据示意图判断是哪种状态。

The transitions between the states can be represented as:

状态之间的转变可以表示为：

Solid ⇌ Liquid ⇌ Gas

固态 ⇌ 液态 ⇌ 气态

Sublimation is the direct change from solid to gas, bypassing the liquid state; the reverse process is called deposition.

升华是固体不经液态直接变为气体的过程；其逆过程称为凝华。

6. Melting and Freezing | 熔化与凝固

Melting is a physical change in which a solid becomes a liquid at its melting point. Energy must be supplied to break the interparticle bonds in the lattice. Remarkably, the temperature remains constant during melting, because the absorbed energy increases the potential energy of the particles, not their average kinetic energy.

熔化是固体在熔点时变为液体的物理变化。必须向系统提供能量以破坏晶格中的粒子间键。值得注意的是，熔化过程温度保持不变，因为吸收的能量增加了粒子的势能，而不是平均动能。

• The melting point of a pure substance equals its freezing point, and it depends on the external pressure. For most substances, increasing pressure raises the melting point; for water, however, the melting point falls very slightly as pressure rises.
• 纯物质的熔点等于其凝固点，并且熔点随外界压强而变化。对于大多数物质，增大压强会使熔点升高；但水例外，压强增大时熔点略微降低。
• During freezing, the reverse happens: thermal energy is released as particles settle into a regular lattice. The temperature again stays constant until all the liquid has frozen.
• 凝固过程恰好相反：粒子排列成规则晶格时释放热能。温度同样保持恒定，直到全部液体凝固完毕。
• A cooling curve of a pure substance shows a horizontal platform at the freezing point, followed by a steady

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