📚 Discovering the Nucleus | 发现原子核
Every atom contains a tiny, dense core called the nucleus. Its discovery completely changed how scientists understand matter. This article explains how experiments revealed the nucleus and what this means for chemistry.
每个原子都包含一个微小而致密的核心，称为原子核。它的发现彻底改变了科学家对物质的理解。本文将解释实验如何揭示原子核，以及这对化学意味着什么。
1. What is an atom? | 什么是原子？
All matter is made of tiny particles called atoms. An atom is the smallest unit of an element that can take part in a chemical reaction.
所有物质都由称为原子的微小粒子组成。原子是元素能参与化学反应的最小单位。
Atoms are mostly empty space, but they contain even smaller subatomic particles. The three main subatomic particles are protons, neutrons, and electrons.
原子内部大部分是空的，但它们包含更小的亚原子粒子。三种主要的亚原子粒子是质子、中子和电子。
Protons and neutrons are found in the centre of the atom, in the nucleus. Electrons move around the outside of the nucleus.
质子和中子位于原子的中心，即原子核内。电子在原子核外运动。
2. Early ideas: the plum pudding model | 早期观点：葡萄干布丁模型
Before the nucleus was discovered, scientists imagined the atom differently. In 1897, J.J. Thomson discovered the electron and proposed a model called the plum pudding model.
在原子核被发现之前，科学家对原子的想象完全不同。1897 年，J.J.汤姆孙发现了电子，并提出了一个称为葡萄干布丁模型的模型。
In this model, the atom was a soft ball of positive charge with negatively charged electrons stuck inside it, like raisins in a plum pudding. There was no hard central core.
在这个模型中，原子是一个带正电的软球，带负电的电子嵌在其中，就像葡萄干布丁中的葡萄干一样。当时认为原子没有坚硬的中心核。
This model was accepted for several years, but it could not explain all experimental evidence. A new experiment was needed to test the structure of the atom.
这个模型被接受了好几年，但它无法解释所有的实验证据。需要一个新实验来检验原子的结构。
3. Rutherford’s gold foil experiment | 卢瑟福的金箔实验
In 1909, Ernest Rutherford and his team, including Hans Geiger and Ernest Marsden, designed a famous experiment. They fired positively charged alpha particles at a very thin sheet of gold foil.
1909 年，欧内斯特·卢瑟福和他的团队，包括汉斯·盖革和欧内斯特·马斯登，设计了一个著名的实验。他们用带正电的 α 粒子轰击一片非常薄的金箔。
Alpha particles are helium nuclei with a positive charge. The gold foil was only a few hundred atoms thick, so the particles could pass through it.
α 粒子是带正电的氦原子核。金箔只有几百个原子那么厚，因此 α 粒子可以穿过它。
Around the foil, a zinc sulfide screen was placed. When an alpha particle hit the screen, it produced a tiny flash of light, allowing the scientists to track where the particles went.
金箔周围放置了硫化锌屏幕。当 α 粒子撞击屏幕时，会产生微小的闪光，使科学家能够追踪粒子的运动方向。
4. Surprising results: most particles pass straight through | 令人惊讶的结果：大多数粒子径直穿过
The team expected most alpha particles to pass through the gold foil with only slight bending. According to the plum pudding model, the positive charge was spread out evenly, so no strong forces should push the particles away.
研究团队预计大多数 α 粒子只会轻微偏转地穿过金箔。根据葡萄干布丁模型，正电荷均匀分布，因此不应有强大的力把粒子推开。
They observed that most alpha particles did pass straight through the foil without changing direction. Some were deflected by small angles, but the majority travelled as if the foil was almost empty.
他们观察到，大多数 α 粒子确实径直穿过金箔而没有改变方向。有些粒子以小角度偏转，但大多数粒子就像穿过几乎空无一物的箔片一样运动。
This result showed that most of the atom is empty space. It did not match the plum pudding model, which imagined the positive charge filling the whole atom.
这个结果表明，原子的大部分是空的。这与葡萄干布丁模型不符，该模型认为正电荷填满了整个原子。
5. A few particles bounce back | 少数粒子反弹回来
Even more surprising was that about 1 in every 8000 alpha particles bounced back towards the source. Some were deflected by very large angles, almost as if they had hit something hard and dense.
更令人惊讶的是，大约每 8000 个 α 粒子中就有 1 个被反弹回射源方向。有些粒子偏转角度非常大，几乎就像撞到了坚硬而致密的东西。
Rutherford described this result with a famous comparison: “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
卢瑟福用一个著名的比喻描述了这个结果：“这几乎就像你向一张薄纸巾发射一枚 15 英寸炮弹，结果它弹回来击中了你一样令人难以置信。”
These rare, large deflections could only be explained if the positive charge and most of the mass were concentrated in a very small region. Rutherford called this region the nucleus.
这些罕见的大角度偏转只能这样解释：正电荷和大部分质量集中在一个非常小的区域内。卢瑟福把这个区域称为原子核。
6. The nuclear model | 核式模型
From the gold foil experiment, Rutherford proposed the nuclear model of the atom. In this model, the atom has a tiny, dense, positively charged nucleus at its centre.
根据金箔实验，卢瑟福提出了原子的核式模型。在这个模型中，原子的中心有一个微小、致密、带正电的原子核。
The nucleus contains almost all of the atom’s mass, but it is much smaller than the whole atom. The atom’s radius is about 10⁻¹⁰ m, while the nucleus is only about 10⁻¹⁴ m across.
原子核几乎包含了原子的全部质量，但它比整个原子小得多。原子的半径约为 10⁻¹⁰ 米，而原子核的直径只有约 10⁻¹⁴ 米。
Electrons move around the nucleus in the surrounding empty space. The positive charge of the nucleus holds the negative electrons in the atom.
电子在原子核周围的空空间中运动。原子核的正电荷将带负电的电子束缚在原子内。
This nuclear model replaced the plum pudding model because it could explain why most alpha particles passed through and why a few bounced back.
核式模型取代了葡萄干布丁模型，因为它能解释为什么大多数 α 粒子穿过，以及为什么少数粒子反弹回来。
7. Inside the nucleus: protons and neutrons | 原子核内部：质子和中子
The nucleus is made of two types of particles: protons and neutrons. Together, they are called nucleons.
原子核由两种粒子组成：质子和中子。它们统称为核子。
Protons have a positive charge of +1 and a relative mass of 1. Neutrons have no charge and a relative mass of 1. Electrons have a negative charge of -1 and a relative mass of about 1/1836.
质子带 +1 的正电荷，相对质量为 1。中子不带电，相对质量也为 1。电子带 -1 的负电荷，相对质量约为 1/1836。
Because protons and neutrons are much heavier than electrons, almost all of the atom’s mass is concentrated in the nucleus.
由于质子和中子比电子重得多，原子的几乎全部质量都集中在原子核内。
8. Atomic number and mass number | 原子序数与质量数
The number of protons in an atom is called the atomic number. It is the most important number because it decides which element the atom belongs to.
原子中质子的数目称为原子序数。它是最重要的数字，因为它决定了原子属于哪种元素。
For example, every carbon atom has 6 protons, so carbon’s atomic number is 6. Any atom with 6 protons must be carbon.
例如，每个碳原子都有 6 个质子，所以碳的原子序数是 6。任何具有 6 个质子的原子一定是碳。
The mass number is the total number of protons and neutrons in the nucleus. It tells you the relative mass of the atom.
质量数是原子核中质子和中子的总数。它告诉你原子的相对质量。
Carbon-12 has 6 protons and 6 neutrons, so its mass number is 12. The symbol ¹²₆C shows the mass number 12 at the top left and the atomic number 6 at the bottom left.
碳-12 有 6 个质子和 6 个中子，所以它的质量数是 12。符号 ¹²₆C 表示左上角的质量数 12 和左下角的原子序数 6。
9. Isotopes: same element, different neutrons | 同位素：同种元素，不同中子
Atoms of the same element always have the same number of protons, but they can have different numbers of neutrons. These different forms are called isotopes.
同一种元素的原子总是具有相同数目的质子，但它们可以具有不同数目的中子。这些不同的形式称为同位素。
Carbon-12 has 6 protons and 6 neutrons. Carbon-14 has 6 protons and 8 neutrons. Both are carbon because they have 6 protons, but they are different isotopes.
碳-12 有 6 个质子和 6 个中子。碳-14 有 6 个质子和 8 个中子。两者都是碳，因为它们都有 6 个质子，但它们是不同的同位素。
Isotopes of the same element have the same chemical properties because chemical behaviour depends on electrons, not neutrons. However, their masses are slightly different.
同一种元素的同位素具有相同的化学性质，因为化学行为取决于电子而不是中子。但它们的质量略有不同。
10. Why the nucleus matters in chemistry | 为什么原子核在化学中重要
The nucleus controls the identity and mass of an atom. The number of protons determines which element you have, and the total number of nucleons determines its mass.
原子核决定了原子的身份和质量。质子数决定你拥有哪种元素，核子总数决定其质量。
In chemical reactions, atoms rearrange their electrons, but the nucleus does not change. This is why elements keep their identity during reactions.
在化学反应中，原子重新排列电子，但原子核不会改变。这就是为什么元素在反应中保持其身份。
The positive charge of the nucleus also attracts electrons and influences how atoms bond with each other. Without the nucleus, atoms and chemical bonds could not exist.
原子核的正电荷还会吸引电子，并影响原子之间如何成键。没有原子核，原子和化学键就不可能存在。
Changes to the nucleus, such as radioactive decay, are not chemical reactions. They are nuclear reactions, which release much more energy than chemical changes.
原子核的变化，如放射性衰变，不是化学反应。它们是核反应，释放的能量远大于化学变化。
11. Key words summary | 关键词总结
The discovery of the nucleus built a clearer picture of the atom. Use the key terms below to check your understanding.
原子核的发现构建了更清晰的原子图像。使用以下关键术语来检查你的理解。
- Nucleus – the tiny, dense, positive centre of an atom | 原子核 – 原子微小、致密、带正电的中心
- Proton – a positive particle found in the nucleus | 质子 – 原子核中带正电的粒子
- Neutron – a neutral particle found in the nucleus | 中子 – 原子核中不带电的粒子
- Electron – a negative particle that moves around the nucleus | 电子 – 在原子核外运动的带负电粒子
- Alpha particle – a positively charged particle used in Rutherford’s experiment | α 粒子 – 卢瑟福实验中使用的带正电粒子
- Atomic number – the number of protons in an atom | 原子序数 – 原子中的质子数
- Mass number – the total number of protons and neutrons | 质量数 – 质子和中子的总数
- Isotope – atoms of the same element with different numbers of neutrons | 同位素 – 同种元素中子数不同的原子
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