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

At the heart of IGCSE Science lies the understanding of matter itself. This article explores the fundamental structure of atoms and how the arrangement of electrons gives rise to the periodic table, a central tool for predicting chemical behaviour and properties.

在 IGCSE 科学的核心，是对物质本身的理解。本文探讨原子的基本结构，以及电子的排布如何构成元素周期表——这一用于预测化学行为与性质的核心工具。

1. The Structure of an Atom | 原子的结构

Every atom consists of a tiny, dense nucleus surrounded by a cloud of electrons. The nucleus contains protons and neutrons, collectively called nucleons.

每个原子都由一个微小而致密的原子核以及环绕其周围的电子云组成。原子核中含有质子和中子，统称为核子。

Protons carry a positive charge, electrons carry an equal negative charge, and neutrons are electrically neutral. Since the number of protons equals the number of electrons in a neutral atom, the overall charge is zero.

质子带正电荷，电子带等量的负电荷，中子不带电。由于中性原子中质子数等于电子数，因此总电荷为零。

2. Subatomic Particles | 亚原子粒子

The properties of the three subatomic particles are summarised in the table below. Remember that their relative masses and charges are taken relative to the proton.

三种亚原子粒子的性质如下表所示。请注意，它们的相对质量和相对电荷都是相对于质子定义的。

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

Particles in the nucleus are held together by a strong force called the strong nuclear force, which overcomes the electrostatic repulsion between positively charged protons.

原子核中的粒子被一种称为“强核力”的强大作用力所束缚，这种力克服了带正电质子之间的静电排斥力。

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

The atomic number (Z) is the number of protons in an atom. It defines the identity of an element. The mass number (A) is the total number of protons and neutrons.

原子序数（Z）是原子中的质子数，它决定了元素的身份。质量数（A）是质子和中子的总数。

Mass number (A) = number of protons + number of neutrons

质量数（A） = 质子数 + 中子数

We can represent a nuclide using the notation ^AZ X, where X is the chemical symbol. For example, ²⁴Mg has 12 protons and 12 neutrons.

我们可以用符号 ^AZ X 来表示一种核素，其中 X 是化学符号。例如，²⁴Mg 有 12 个质子和 12 个中子。

In a neutral atom, the number of electrons equals the number of protons. For ions, the charge indicates the difference between protons and electrons.

在中性原子中，电子数等于质子数。对于离子，电荷表示质子数与电子数之差。

4. Isotopes | 同位素

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

同位素是同一元素中具有相同质子数但不同中子数的原子。因此，它们具有相同的原子序数但不同的质量数。

For example, carbon exists as three isotopes: ¹²C, ¹³C and ¹⁴C. All have 6 protons, but the number of neutrons is 6, 7 and 8 respectively.

例如，碳存在三种同位素：¹²C、¹³C 和 ¹⁴C。它们都有 6 个质子，但中子数分别为 6、7 和 8。

Isotopes of an element have the same chemical properties because they have the same electronic configuration. However, physical properties, such as density and rate of diffusion, can differ slightly.

同一元素的同位素具有相同的化学性质，因为它们具有相同的电子排布。然而，物理性质如密度和扩散速率会略有不同。

5. Electronic Configuration | 电子排布

Electrons occupy energy levels (shells) around the nucleus. The first shell holds a maximum of 2 electrons; the second and third shells hold a maximum of 8 electrons each.

电子占据原子核周围的能层（电子壳层）。第一壳层最多容纳 2 个电子；第二和第三壳层最多各容纳 8 个电子。

Electrons fill the shells from innermost to outermost. For example, sodium (Na, Z=11) has the configuration 2.8.1.

电子从内到外填充壳层。例如，钠（Na，Z=11）的排布为 2.8.1。

The outermost shell is called the valence shell. The number of valence electrons determines the chemical reactivity of an element.

最外层壳层称为价电子层。价电子数决定了元素的化学反应活性。

Electron shell capacity: 2, 8, 8

电子壳层容量：2、8、8

You can deduce the group and period of an element from its configuration: the number of outer electrons gives the group (for Groups 1-2 and 13-18) and the number of shells gives the period.

你可以从元素的电子排布推断其族和周期：最外层电子数对应族（对于第 1-2 族和第 13-18 族），壳层数对应周期。

6. The Periodic Table: Groups and Periods | 元素周期表：族和周期

The periodic table arranges elements in order of increasing atomic number. Elements with similar properties appear in vertical columns called groups. Horizontal rows are called periods.

元素周期表按照原子序数递增排列元素。具有相似性质的元素排列在称为“族”的纵列中。水平行称为“周期”。

Group number (IUPAC 1-18) helps predict valence electrons and reactivity.

族号（IUPAC 1-18）有助于预测价电子数和反应活性。
Period number indicates the number of occupied electron shells.

周期数表示已占据的电子壳层数目。
Metals are found on the left and centre; non-metals on the right.

金属位于左侧和中部；非金属位于右侧。

The modern table also includes the lanthanides and actinides as separate blocks below the main table.

现代周期表还将镧系元素和锕系元素作为单独区块置于主表下方。

7. Group 1: Alkali Metals | 第 1 族：碱金属

Group 1 elements (lithium, sodium, potassium, rubidium, caesium) are soft, highly reactive metals with one outer electron.

第 1 族元素（锂、钠、钾、铷、铯）是柔软、高反应活性的金属，具有一个外层电子。

Reactivities increase down the group. This is because the outer electron gets further from the nucleus and is more easily lost, with greater shielding from inner shells.

反应活性自上而下递增。这是因为外层电子离核更远，同时内层壳层的屏蔽效应更大，因此更容易失去电子。

Alkali metals react with water to form a hydroxide solution and hydrogen gas. For example, sodium reacts vigorously, producing sodium hydroxide and hydrogen.

碱金属与水反应生成氢氧化物溶液和氢气。例如，钠剧烈反应，产生氢氧化钠和氢气。

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

All Group 1 metals form ions with a charge of +1 by losing their single valence electron.

所有第 1 族金属通过失去唯一的价电子形成 +1 价离子。

8. Group 7: Halogens | 第 7 族：卤素

Group 7 elements (fluorine, chlorine, bromine, iodine) are non-metals with seven valence electrons. They gain one electron to form a -1 ion.

第 7 族元素（氟、氯、溴、碘）是具有七个价电子的非金属。它们获得一个电子形成 -1 价离子。

Reactivity decreases down the group. As atoms get larger, the outer shell is further from the nucleus, making it harder for the atom to attract an extra electron.

反应活性自上而下递减。随着原子变大，外层电子壳层离核更远，使得原子更难吸引额外的电子。

Halogens exist as diatomic molecules (F₂, Cl₂, Br₂, I₂). At room temperature, chlorine is a yellow-green gas, bromine a reddish-brown liquid, and iodine a dark grey solid.

卤素以双原子分子存在（F₂、Cl₂、Br₂、I₂）。室温下，氯是黄绿色气体，溴是红棕色液体，碘是深灰色固体。

A more reactive halogen can displace a less reactive one from its salt solution. For example, chlorine displaces bromine from potassium bromide solution.

更活泼的卤素可以从其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(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq)

9. Group 0: Noble Gases | 第 0 族：稀有气体

Group 0 elements (helium, neon, argon, krypton, xenon) have full outer shells. This gives them a stable electronic configuration, making them very unreactive.

第 0 族元素（氦、氖、氩、氪、氙）具有满外层电子壳层。这赋予了它们稳定的电子排布，使它们非常不活泼。

They exist as monatomic gases and have low boiling points. The boiling points increase down the group as the strength of London dispersion forces increases with atom size.

它们以单原子气体存在，沸点很低。沸点自上而下升高，因为随着原子尺寸增大，伦敦色散力强度增加。

Noble gases are used in discharge tubes, such as neon signs, and provide an inert atmosphere for welding or chemical reactions.

稀有气体用于气体放电管（如霓虹灯），并为焊接或化学反应提供惰性气氛。

Full shell ⇒ stable ⇒ low reactivity

满壳层 ⇒ 稳定 ⇒ 低反应活性

10. Trends in the Periodic Table | 元素周期表中的递变规律

Across a period, atomic radius decreases from left to right. The increasing nuclear charge pulls the electrons closer, even though the number of shells stays the same.

在同一周期中，从左到右原子半径减小。虽然壳层数不变，但增大的核电荷将电子拉得更近。

Down a group, atomic radius increases due to the addition of new electron shells.

在族中自上而下，原子半径增加，因为增加了新的电子壳层。

Electronegativity (the ability of an atom to attract electrons in a covalent bond) increases across a period and decreases down a group.

电负性（原子在共价键中吸引电子的能力）在同一周期中递增，在同一族中递减。

Metallic character decreases across a period and increases down a group. Non-metallic character shows the opposite trend.

金属性在同一周期中递减，在同一族中递增。非金属性则相反。

Ionisation energy (energy required to remove one electron) generally increases across a period and decreases down a group.

电离能（移除一个电子所需的能量）在同一周期中一般递增，在同一族中递减。

Understanding these trends allows you to predict the behaviour of unfamiliar elements and is a key exam skill for IGCSE Science.

理解这些递变规律使你能预测未知元素的行为，这也是 IGCSE 科学中的一项关键考试技能。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

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