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

In IGCSE Science (Edexcel), the topic of atomic structure and the periodic table is the foundation of all chemistry. Understanding how protons, neutrons and electrons are arranged, and how this arrangement determines an element’s position in the periodic table, will help you explain bonding, reactions and trends with confidence.

在 IGCSE 科学（爱德思）中，原子结构与元素周期表是全部化学知识的基础。理解质子、中子和电子如何排列，以及这种排列如何决定元素在周期表中的位置，能够帮助你自信地解释成键、反应和递变规律。

1. The Tiny Atom | 微观原子

An atom is the smallest particle of an element that can take part in a chemical reaction. It is incredibly small — over ten million atoms could fit across a single full stop. Despite its tiny size, every atom has a definite structure: a central nucleus surrounded by orbiting electrons.

原子是能参与化学反应的元素的最小粒子。它极其微小——一个句号上就能排布超过一千万个原子。尽管体积很小，每个原子都有确定的结构：一个位于中心的原子核，周围环绕着运动的电子。

The atom is neutral overall because the positive charge of the protons exactly balances the negative charge of the electrons. The nucleus is very dense and contains almost all of the atom’s mass.

原子整体呈电中性，因为质子所带的正电荷恰好抵消了电子所带的负电荷。原子核密度非常大，几乎集中了原子的全部质量。

2. Subatomic Particles | 亚原子粒子

Atoms are made from three subatomic particles: protons, neutrons and electrons. You must know their relative charge, relative mass and location perfectly for the exam.

原子由三种亚原子粒子构成：质子、中子和电子。你必须清楚记得它们的相对电荷、相对质量和所在位置，这对考试至关重要。

Particle	Relative Charge	Relative Mass	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	-1	1/1836 (almost 0)	Electron shells

Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral. Because electrons have almost no mass, nearly all the mass of an atom comes from the protons and neutrons in the nucleus.

质子带正电荷，电子带负电荷，中子不带电荷。由于电子几乎没有质量，原子的几乎所有质量都来自原子核中的质子和中子。

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

Every element is defined by its atomic number, which is the number of protons in the nucleus. In a neutral atom, the number of electrons equals the number of protons, so the atomic number also tells you the number of electrons.

每种元素都由其原子序数定义，即原子核中的质子数。在电中性原子中，电子数等于质子数，因此原子序数也告诉你电子数目。

The mass number is the total number of protons plus neutrons. You can calculate the number of neutrons by subtracting the atomic number from the mass number.

质量数是质子数与中子数之和。你可以用质量数减去原子序数来计算中子数目。

Mass number = Atomic number + Number of neutrons

质量数 = 原子序数 + 中子数

For example, sodium has an atomic number of 11 and a mass number of 23. This means it has 11 protons, 11 electrons and 12 neutrons (23 – 11 = 12). This is written as ²³₁₁Na.

例如，钠的原子序数为 11，质量数为 23。这意味着它有 11 个质子、11 个电子和 12 个中子（23 – 11 = 12）。写作 ²³₁₁Na。

4. Isotopes | 同位素

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Because they have the same number of protons and electrons, they have the same chemical properties; because their masses differ, their physical properties may differ slightly.

同位素是指同一种元素中具有相同质子数但不同中子数的原子。由于质子和电子数目相同，它们的化学性质相同；由于质量不同，物理性质可能略有差异。

Common examples include carbon-12 and carbon-14:

常见例子包括碳-12 和碳-14：

Carbon-12 (¹²₆C): 6 protons, 6 neutrons, 6 electrons.

碳-12（¹²₆C）：6 个质子、6 个中子、6 个电子。
Carbon-14 (¹⁴₆C): 6 protons, 8 neutrons, 6 electrons.

碳-14（¹⁴₆C）：6 个质子、8 个中子、6 个电子。

Isotopes have important uses. Carbon-14 is used in radiocarbon dating to determine the age of ancient materials, while cobalt-60 is used in radiotherapy to treat cancer.

同位素具有重要用途。碳-14 用于放射性碳测年，以确定古代材料的年代；钴-60 则用于放射疗法治疗癌症。

5. Electron Configuration | 电子排布

Electrons are arranged in shells (energy levels) around the nucleus. The shells fill from the inside out: the first shell holds a maximum of 2 electrons, the second shell holds 8, and the third shell holds 8 for the elements you study at IGCSE.

电子围绕原子核排列在壳层（能级）中。壳层从内到外依次填充：第一层最多容纳 2 个电子，第二层最多容纳 8 个，在 IGCSE 所学元素中第三层最多容纳 8 个。

For example, sodium (11 electrons) has the configuration 2,8,1. This means 2 electrons in the first shell, 8 in the second shell, and 1 in the outer shell. Chlorine (17 electrons) has the configuration 2,8,7.

例如，钠（11 个电子）的排布为 2,8,1，即第一层 2 个、第二层 8 个、最外层 1 个。氯（17 个电子）的排布为 2,8,7。

The number of electrons in the outermost shell determines how an element reacts. Elements with a full outer shell, such as the noble gases, are very stable and unreactive.

最外层电子数决定了元素的反应行为。最外层充满电子的元素，如稀有气体，非常稳定且不易反应。

6. The Layout of the Periodic Table | 周期表的布局

The periodic table arranges all known elements in order of increasing atomic number. Elements with similar properties are placed in vertical columns called groups, while horizontal rows are called periods.

元素周期表按照原子序数递增的顺序排列所有已知元素。性质相似的元素放在称为族的纵列中，而行称为周期。

In the Edexcel IGCSE course, you need to recognise the positions of metals and non-metals, and locate elements using their group and period numbers. The metals are found on the left and in the middle, while non-metals are found on the right.

在爱德思 IGCSE 课程中，你需要识别金属和非金属的位置，并根据族和周期序号定位元素。金属位于左侧和中部，非金属位于右侧。

The staircase line (sometimes called the zig-zag line) separates metals from non-metals. Elements touching this line, such as silicon, often have properties of both groups and are called metalloids.

阶梯线（有时称为锯齿线）将金属与非金属分开。与这条线相邻的元素，如硅，通常兼具两类性质，被称为类金属（准金属）。

7. Periods and Groups | 周期与族

Two key rules link electron configuration to the periodic table:

两条关键规则将电子排布与周期表联系起来：

The group number equals the number of electrons in the outer shell.

族序号等于最外层电子数。
The period number equals the number of occupied electron shells.

周期序号等于电子层数。

For example, magnesium has the configuration 2,8,2, so it is in Group 2, Period 3. This rule works for Group 1, 2, 7 and 0 in the Edexcel specification.

例如，镁的电子排布为 2,8,2，因此它位于第 2 族、第 3 周期。这条规则适用于爱德思考纲中的第 1、2、7、0 族。

Moving across a period from left to right, the elements change from metallic to non-metallic. Moving down a group, the elements show similar chemical properties because their outer shell electron numbers are the same.

在同一周期中从左到右移动，元素由金属性逐渐变为非金属性。在同一族中向下移动，由于最外层电子数相同，元素表现出相似的化学性质。

8. Metals vs Non-metals | 金属与非金属

You should be able to compare the physical properties of metals and non-metals and connect these to their positions on the periodic table.

你应该能够比较金属与非金属的物理性质，并将这些性质与它们在周期表中的位置联系起来。

Property	Metal	Non-metal
Appearance	Shiny / lustrous	Dull
Malleability	Malleable and ductile	Brittle when solid
Conduction	Good conductor of heat and electricity	Poor conductor (except graphite)
Melting point	Usually high	Usually low

In chemical reactions, metal atoms tend to lose electrons to form positive ions (cations). Non-metal atoms tend to gain electrons to form negative ions (anions).

在化学反应中，金属原子倾向于失去电子形成正离子（阳离子）；非金属原子倾向于得到电子形成负离子（阴离子）。

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

Group 1 contains lithium, sodium and potassium, which we study in detail at IGCSE. These elements are soft solids at room temperature and have relatively low densities; lithium, sodium and potassium all float on water.

第 1 族包含锂、钠和钾，IGCSE 会重点学习它们。这些元素在室温下是柔软的固体，密度较小；锂、钠、钾都能浮在水面上。

Alkali metals react vigorously with water to produce hydrogen gas and an alkaline hydroxide solution. For example:

碱金属与水剧烈反应，生成氢气和碱性的氢氧化物溶液。例如：

2Na + 2H₂O → 2NaOH + H₂

Reactivity increases as you go down the group. This is because the outer electron is further from the nucleus and is more easily lost, so the shielding by inner shells increases.

随着族内自上而下，反应活性逐渐增强。原因是外层电子距离原子核更远，更容易失去，同时内层电子的屏蔽效应增大。

All Group 1 elements have one outer-shell electron, so they all lose one electron in reactions, forming +1 ions with a stable noble gas configuration.

所有第 1 族元素都只有一个最外层电子，因此它们在反应中都失去一个电子，形成具有稳定稀有气体构型的 +1 价离子。

10. Group 7: The Halogens | 第7族：卤素

Group 7 contains fluorine, chlorine, bromine and iodine. These non-metals exist as diatomic molecules and become less reactive as you go down the group.

第 7 族包含氟、氯、溴和碘。这些非金属以双原子分子形式存在，并且随着族内自上而下，反应活性逐渐减弱。

Chlorine is a green gas.

氯气是黄绿色气体。
Bromine is a red-brown liquid.

溴是红棕色液体。
Iodine is a dark grey solid that sublimes to a purple vapour.

碘是深灰色固体，升华后产生紫色蒸气。

Halogens have seven outer-shell electrons, so they gain one electron in reactions to form -1 ions. A more reactive halogen can displace a less reactive halogen from a solution of its salt. For example, chlorine displaces bromine from potassium bromide solution.

卤素最外层有 7 个电子，因此它们在反应中得到一个电子形成 -1 价离子。较活泼的卤素可以将较不活泼的卤素从其盐溶液中置换出来。例如，氯气可以从溴化钾溶液中置换出溴。

Cl₂ + 2KBr → 2KCl + Br₂

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

Group 0 contains helium, neon and argon. These gases are chemically unreactive because their outer electron shells are completely full. This makes them very stable and explains why they exist as single atoms.

第 0 族包含氦、氖和氩。这些气体在化学上非常不活泼，因为它们的最外层电子已经充满。这使它们非常稳定，也解释了它们为什么以单原子形式存在。

Because they are unreactive, noble gases have useful applications:

由于不活泼，稀有气体有很多实际用途：

Helium is used in weather balloons and airships because it is less dense than air and does not burn.

氦气用于气象气球和飞艇，因为它比空气轻且不可燃。
Neon is used in advertising signs because it glows brightly when an electric current passes through it.

氖用于广告灯牌，因为通电时它会发出明亮的辉光。
Argon is used in filament light bulbs and welding because it does not react with the hot metal.

氩用于白炽灯和焊接，因为它不与高温金属发生反应。

Although noble gases are unreacted in normal conditions, they do show a trend: as you go down the group, their boiling points increase because the atoms become larger and the intermolecular forces become stronger.

虽然稀有气体在通常条件下不反应，但它们的沸点随族内自上而下逐渐升高，因为原子变大，分子间作用力增强。

12. Exam Tips and Common Mistakes | 考试技巧与常见错误

Many students lose marks by mixing up atomic number and mass number. Remember: atomic number = protons only; mass number = protons + neutrons.

很多学生因为混淆原子序数和质量数而丢分。请记住：原子序数 = 质子数；质量数 = 质子数 + 中子数。

Another common error is writing the electron configuration of ions instead of atoms. For a neutral atom, the number of electrons always equals the number of protons.

另一个常见错误是写出离子的电子排布而不是原子的。对于电中性原子，电子数始终等于质子数。

When explaining trends in Group 1 and Group 7, always link the trend to the distance of the outer shell from the nucleus and the shielding effect. Do not just say “the atoms get bigger.”

在解释第 1 族和第 7 族的递变规律时，一定要将规律与外层电子距原子核的距离以及屏蔽效应联系起来，不能只说”原子变大”。

Finally, practise writing balanced symbol equations for the reactions of alkali metals with water and for halogen displacement reactions. These appear frequently in the written exams.

最后，请反复练习书写碱金属与水反应以及卤素置换反应的配平符号方程式。这些内容在笔试中经常出现。

By mastering atomic structure and the periodic table, you will have a strong foundation for the rest of the IGCSE Science course. Good luck with your revision!

掌握原子结构和元素周期表，你就为 IGCSE 科学课程的其余内容打下了坚实基础。祝你复习顺利！

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