Inside the Atom | 原子内部探秘

📚 Inside the Atom | 原子内部探秘

Atoms are often described as the smallest neutral particles that take part in chemical reactions, but the inside of an atom has its own complex structure. Understanding this structure is fundamental to explaining periodicity, bonding, and reactivity in A Level Chemistry.

原子通常被描述为参与化学反应的最小中性粒子，但原子内部有着自身复杂的结构。理解这一结构是解释元素周期性、化学键和反应活性的基础，也是 A Level 化学的核心内容。

1. The Nuclear Atom | 核式原子

The modern nuclear atom has a tiny, dense, positively charged nucleus containing protons and neutrons, surrounded by a much larger volume of negative electrons. Rutherford’s gold foil experiment provided key evidence: most alpha particles passed straight through, but a few were deflected through large angles.

现代核式原子由一个极小、致密、带正电的原子核（含质子和中子）和在其周围更大空间内运动的负电子组成。卢瑟福的金箔实验提供了关键证据：大多数 α 粒子径直穿过，但少数发生大角度偏转。

Rutherford concluded that the atom is mostly empty space, with almost all the mass concentrated in a positively charged nucleus. This overturned the earlier plum pudding model.

卢瑟福得出结论：原子大部分是空的，几乎全部质量集中在一个带正电的原子核中。这推翻了早期的葡萄干布丁模型。

---

2. Subatomic Particles | 亚原子粒子

Protons, neutrons, and electrons differ in relative mass and charge. The proton and neutron are nucleons found in the nucleus, while electrons occupy the surrounding space.

质子、中子和电子的相对质量与电荷不同。质子和中子统称为核子，位于原子核内，而电子占据核外空间。

Particle 粒子	Relative mass 相对质量	Relative charge 相对电荷	Position 位置
Proton 质子	1	+1	Nucleus 原子核
Neutron 中子	1	0	Nucleus 原子核
Electron 电子	1/1840	-1	Shells 壳层

Because the proton and neutron have almost equal masses, the mass of an atom is effectively determined by its nucleons. The electron contributes negligible mass but determines chemical behaviour.

由于质子和中子的质量几乎相等，原子的质量实际上由核子决定。电子质量可以忽略，但决定化学行为。

---

3. Atomic Number and Mass Number | 原子序数与质量数

The atomic number Z is the number of protons in the nucleus and defines the element. The mass number A is the total number of protons plus neutrons.

原子序数 Z 是原子核中的质子数，决定元素种类。质量数 A 是质子数与中子数之和。

A = Z + N

其中 N 为中子数。

For a neutral atom, the number of electrons equals the number of protons, so the positive and negative charges balance.

对于中性原子，电子数等于质子数，因此正负电荷相互抵消。

For example, ¹²₆C has 6 protons, 6 neutrons, and 6 electrons. The symbol ¹²C is often used because the atomic number is fixed for carbon.

例如，¹²₆C 有 6 个质子、6 个中子和 6 个电子。由于碳的原子序数是固定的，通常也写作 ¹²C。

---

4. Isotopes | 同位素

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They therefore have the same atomic number but different mass numbers.

同位素是同种元素中质子数相同而中子数不同的原子。因此它们原子序数相同，但质量数不同。

Chlorine has two common isotopes, ³⁵Cl and ³⁷Cl, both with 17 protons but with 18 and 20 neutrons respectively. Carbon also has isotopes such as ¹²C and ¹⁴C.

氯有两种常见同位素 ³⁵Cl 和 ³⁷Cl，二者都有 17 个质子，但分别有 18 个和 20 个中子。碳也有 ¹²C 和 ¹⁴C 等同位素。

Isotopes have identical chemical properties because electron arrangement is the same, but slightly different physical properties due to different masses.

同位素的化学性质相同，因为电子排布相同；但由于质量不同，物理性质略有差异。

---

5. Relative Atomic Mass | 相对原子质量

Relative atomic mass Aᵣ is the weighted average mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom. Since most elements consist of isotopes, Aᵣ is rarely a whole number.

相对原子质量 Aᵣ 是元素一个原子的加权平均质量相对于碳-12 原子质量的 1/12。由于大多数元素由同位素组成，Aᵣ 通常不是整数。

Aᵣ = Σ (isotopic mass × percentage abundance) ÷ 100

相对原子质量 = Σ（同位素质量 × 丰度百分比）÷ 100。

For example, chlorine has 75% ³⁵Cl and 25% ³⁷Cl, giving Aᵣ = (35 × 75 + 37 × 25) ÷ 100 = 35.5.

例如，氯含有 75% 的 ³⁵Cl 和 25% 的 ³⁷Cl，因此 A

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）