Atomic Structure and the Periodic Table | 原子结构与元素周期表

📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表

Understanding atomic structure is fundamental to mastering chemistry. The arrangement of protons, neutrons and electrons inside an atom determines the element’s identity, its chemical properties and its position in the periodic table. This article explains the core concepts you need for Edexcel IGCSE Science.

理解原子结构是掌握化学的基础。原子内部质子、中子和电子的排列决定了元素的身份、化学性质以及在周期表中的位置。本文解释你在 Edexcel IGCSE 科学考试中需要的核心概念。

1. Development of the Atom Model | 原子模型的发展

The atomic model has evolved over time. John Dalton proposed that atoms were solid, indivisible spheres. Later, J.J. Thomson discovered the electron and suggested the ‘plum pudding’ model, where negative electrons were scattered inside a positive cloud.

原子模型是随着时间不断发展的。约翰·道尔顿提出原子是实心的不可分割的球体。后来 J·J·汤姆森发现了电子，并提出了“葡萄干布丁”模型，认为带负电的电子散布在带正电的云团内。

Ernest Rutherford’s gold foil experiment showed that most of the atom is empty space, with a tiny, dense, positive nucleus. Niels Bohr then placed electrons in fixed orbits around the nucleus. This is the model you study today.

欧内斯特·卢瑟福的金箔实验表明，原子的大部分是空的空间，原子中心有一个极小且致密的正电荷核。尼尔斯·玻尔随后提出电子围绕原子核在固定轨道上运行。这就是你如今学习的模型。

The modern model treats electron positions as regions of probability known as orbitals. For IGCSE, you often use the Bohr model with numbered shells.

现代模型将电子的位置视为概率区域，称为轨道。对于 IGCSE，你通常使用带有编号壳层的玻尔模型。

2. Atomic Structure: Protons, Neutrons and Electrons | 原子结构：质子、中子与电子

All atoms are made from three subatomic particles. The proton carries a relative charge of +1 and has a relative mass of 1. The neutron has no charge and a relative mass of 1. The electron carries a relative charge of –1 and a relative mass of 1/1836 (effectively 0).

所有原子都由三种亚原子粒子构成。质子带 +1 相对电荷，相对质量为 1。中子不带电荷，相对质量为 1。电子带 –1 相对电荷，相对质量约为 1/1836（实际上可视为 0）。

In an atom, the number of protons equals the number of electrons. This keeps the atom neutral. If the numbers differ, the particle is an ion, not an atom.

在原子中，质子数等于电子数，从而保持原子呈电中性。如果二者数量不同，该粒子就是离子，而不是原子。

Particle \| 粒子	Relative Charge \| 相对电荷	Relative Mass \| 相对质量
Proton 质子	+1	1
Neutron 中子	0	1
Electron 电子	–1	1/1836

Protons and neutrons are found in the nucleus. Electrons move in shells around the nucleus. The nucleus is tiny compared to the whole atom but contains almost all its mass.

质子和中子位于原子核内。电子在原子核周围的壳层中运动。原子核相对于整个原子来说非常小，但却几乎包含了原子的全部质量。

3. Atomic Number and Mass Number | 原子序数（质子数）与质量数

Every element is defined by its atomic number (Z), which is the number of protons in its nucleus. The mass number (A) is the total number of protons and neutrons in the nucleus.

每种元素都由其原子序数（Z）定义，原子序数即原子核中的质子数。质量数（A）是原子核中质子数与中子数的总和。

For an atom, the number of electrons is also equal to the atomic number. To find the number of neutrons, subtract the atomic number from the mass number:

对于原子而言，电子数也等于原子序数。要找出中子数，用质量数减去原子序数即可：

Neutron number = Mass number – Atomic number
中子数 = 质量数 − 原子序数

For example, sodium has atomic number 11 and mass number 23. It contains 11 protons, 11 electrons and 12 neutrons.

例如，钠的原子序数为 11，质量数为 23。它含有 11 个质子、11 个电子和 12 个中子。

4. Isotopes | 同位素

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Because the proton number is fixed, their chemical properties are almost identical. However, the physical properties such as mass can differ.

同位素是同一元素的原子，它们质子数相同而中子数不同。由于质子数固定，它们的化学性质几乎完全相同。然而，诸如质量之类的物理性质可能有所不同。

A common example is carbon-12 and carbon-14. Both have 6 protons, but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons.

一个常见例子是碳-12 和碳-14。二者都有 6 个质子，但碳-12 有 6 个中子，碳-14 有 8 个中子。

₁₂C: 6 protons, 6 electrons, 6 neutrons
₁₄C: 6 protons, 6 electrons, 8 neutrons

Isotopes are used in medicine, archaeology and industry. For example, carbon-14 is used for dating ancient organic materials.

同位素应用于医学、考古学和工业领域。例如，碳-14 用于测定古代有机材料的年代。

5. Electronic Configuration | 电子排布

Electrons occupy shells (energy levels) around the nucleus. The first shell can hold up to 2 electrons, the second and third shells can hold up to 8 electrons each.

电子占据原子核周围的壳层（能级）。第一壳层最多可容纳 2 个电子，第二和第三壳层最多各可容纳 8 个电子。

Electrons fill the shells from the innermost outward, and the outermost shell is called the valence shell. The number of electrons in the valence shell determines the chemical behaviour of the element.

电子从最内层开始向外填充，最外层壳层称为价壳层。价壳层中的电子数决定了该元素的化学行为。

For example, the electronic configuration of oxygen (atomic number 8) is 2,6. That of magnesium (atomic number 12) is 2,8,2.

例如，氧（原子序数 8）的电子排布是 2,6。镁（原子序数 12）的电子排布是 2,8,2。

O: 2,6 Mg: 2,8,2

You should be able to draw shell diagrams and write these configurations quickly for elements up to atomic number 20.

你应该能够画出壳层图，并迅速写出原子序数至 20 的元素排布。

6. Structure of the Periodic Table | 周期表的结构

The periodic table arranges elements in order of increasing atomic number. Each horizontal row is called a period, and each vertical column is called a group.

周期表按原子序数递增的顺序排列元素。每一横行称为一个周期，每一纵列称为一个族。

Elements in the same group have the same number of electrons in their outer shell, so they show similar chemical properties. For example, Group 1 elements all have one outer electron, and Group 7 elements all have seven outer electrons.

同一族的元素具有相同的最外层电子数，因此表现出相似的化学性质。例如，第 1 族元素都只有 1 个外层电子，第 7 族元素都有 7 个外层电子。

As you go down a group, the number of occupied shells increases, so atomic radius increases. As you go across a period, protons increase and the outer shell remains the same, so atoms generally become smaller and the number of outer electrons increases from 1 to 8.

在同一族中从上到下，占据的壳层数增加，因此原子半径增大。在同一周期中从左到右，质子数增加而壳层数不变，因此原子通常变小，外层电子数从 1 增加到 8。

7. Periods and Groups | 周期与族

The period number tells you how many electron shells are occupied in an atom. For example, all elements in Period 3 have three electron shells.

周期数告诉你一个原子占据了多少个电子壳层。例如，第三周期的所有元素都有三个电子壳层。

The group number (for groups 1, 2 and 7) tells you the number of outer electrons. Group 1 elements have 1 outer electron, Group 2 have 2 outer electrons, and Group 7 have 7 outer electrons.

族号（对于第 1、2 和 7 族）告诉你外层电子数。第 1 族元素有 1 个外层电子，第 2 族有 2 个外层电子，第 7 族有 7 个外层电子。

For Group 0 (noble gases), the atoms have full outer shells, making them very stable and unreactive. Group 0 is sometimes called Group 8/18 in modern naming.

对于第 0 族（稀有气体），其原子具有全满的外壳层，因此非常稳定、不活泼。第 0 族在现代命名中有时称为第 8/18 族。

You can predict the charge of an ion from its group. Group 1 atoms lose 1 electron to form +1 ions. Group 2 atoms lose 2 electrons to form +2 ions. Group 6 atoms gain 2 electrons to form –2 ions, and Group 7 atoms gain 1 electron to form –1 ions.

你可以根据族号预测离子所带的电荷。第 1 族原子失去 1 个电子形成 +1 离子。第 2 族原子失去 2 个电子形成 +2 离子。第 6 族原子获得 2 个电子形成 –2 离子，第 7 族原子获得 1 个电子形成 –1 离子。

8. Metals and Non-metals | 金属与非金属

The periodic table can be divided into metals and non-metals. Metals are usually found on the left and centre of the table, while non-metals are on the top right. Metalloids, such as silicon, sit along the step line between them.

周期表可以分为金属和非金属。金属通常位于表的左侧和中部，非金属位于右上方。类金属（如硅）位于二者之间的阶梯线附近。

Metals are shiny, malleable, good conductors of heat and electricity, and have high melting points (except mercury). Non-metals are usually dull, brittle, poor conductors and have lower melting points.

金属有光泽、具有延展性、是良好的热和电导体，并且熔点较高（汞除外）。非金属通常暗淡、脆硬、导电性差并且熔点较低。

In chemical reactions, metals tend to lose electrons to form positive ions. Non-metals tend to gain electrons to form negative ions or share electrons in covalent bonds.

在化学反应中，金属倾向于失去电子形成正离子。非金属倾向于获得电子形成负离子，或通过共价键共享电子。

Metal: sodium, iron, copper | 金属：钠、铁、铜
Non-metal: oxygen, carbon, chlorine | 非金属：氧、碳、氯

9. Group 1: The Alkali Metals | 第 1 族：碱金属

Group 1 elements are soft, low-density metals that react rapidly with water and oxygen. They all have one electron in their outer shell, which they readily lose to form a +1 ion.

第 1 族元素是柔软、低密度的金属，能迅速与水、氧气反应。它们的最外层只有 1 个电子，容易失去这个电子形成 +1 离子。

Reactivity increases as you go down the group. Lithium fizzes gently, sodium melts into a ball and whizzes around, and potassium burns with a lilac flame. The trend arises because the outer electron is further from the nucleus and is more easily lost.

活泼性随原子序数增大而增强。锂在水面上轻轻冒泡，钠熔成小球并快速游动，钾发出淡紫色火焰并燃烧。这个趋势是因为外层电子离原子核更远，更容易被失去。

Alkali metals form ionic compounds with non-metals. For example, sodium reacts with chlorine to form sodium chloride, NaCl.

碱金属与非金属形成离子化合物。例如，钠与氯反应生成氯化钠，NaCl。

2Na(s) + Cl₂(g) → 2NaCl(s)

10. Group 7: The Halogens | 第 7 族：卤素

Group 7 elements are diatomic non-metals that exist as molecules such as F₂, Cl₂, Br₂ and I₂. They have seven outer electrons and need one more electron to achieve a stable noble gas configuration. They form –1 ions.

第 7 族元素是双原子非金属，以分子形式存在，如 F₂、Cl₂、Br₂ 和 I₂。它们有 7 个外层电子，需要再获得 1 个电子以形成稳定的稀有气体排布。它们形成 –1 离子。

Reactivity decreases as you go down the group. Fluorine is the most reactive, while iodine is the least. The trend happens because the incoming electron is further from the nucleus and less easily attracted when the atom is larger.

活泼性随原子序数增大而降低。氟最活泼，碘最不活泼。这是因为对于更大原子，获取的电子离原子核更远，较难被吸引。

More reactive halogens can displace less reactive halogens from their salts. For example, chlorine can displace bromine from potassium bromide solution:

更活泼的卤素可以从盐溶液中置换出较不活泼的卤素。例如，氯可以从溴化钾溶液中置换出溴：

Cl₂(g) + 2KBr(aq) → 2KCl(aq) + Br₂(aq)

11. Group 0: The Noble Gases | 第 0 族：稀有气体

Noble gases are colourless, odourless and unreactive. Their outer shells are full: helium has 2 outer electrons, while neon and argon have 8. This full shell gives them a very stable electronic configuration.

稀有气体无色、无味且不活泼。它们的外层电子排布是全满的：氦有 2 个外层电子，氖和氩有 8 个。这种全满的排布使得它们具有非常稳定的电子结构。

They exist as single atoms (monatomic gases) because they do not need to bond with other atoms. Their melting and boiling points are very low, increasing slightly down the group.

它们以单原子气体形式存在，因为不需要与其他原子成键。它们的熔点和沸点非常低，并随原子序数增大而略微升高。

Noble gases are used in lighting, welding and advertising signs. Argon is used in some types of welding to provide an inert atmosphere, which prevents unwanted reactions.

稀有气体用于照明、焊接和广告灯牌。氩用于某些焊接中以提供惰性气氛，防止发生不必要的反应。

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Atomic Structure and the Periodic Table | 原子结构与元素周期表