Boron, Carbon, Nitrogen: Period 2 Neighbours (Z = 5, 6, 7) | 硼、碳、氮：第二周期的邻居（Z = 5、6、7）

📚 Boron, Carbon, Nitrogen: Period 2 Neighbours (Z = 5, 6, 7) | 硼、碳、氮：第二周期的邻居（Z = 5、6、7）

Every element in the universe is defined by one simple number: its atomic number (Z). For IGCSE Edexcel Science students, the atomic number is the key that unlocks the entire periodic table. In this article, we zoom in on three fascinating neighbours in Period 2 — boron (Z = 5), carbon (Z = 6) and nitrogen (Z = 7). Although they sit side by side, these three elements display a beautifully predictable change in electron arrangement, bonding and chemical behaviour — exactly the kind of trend the examiners love to test.

宇宙中的每一种元素都由一个简单而独特的数字所定义：原子序数（Z）。对于 IGCSE Edexcel 科学学生而言，原子序数是打开整张元素周期表的钥匙。本文将聚焦于第二周期中三位迷人的邻居——硼（Z = 5）、碳（Z = 6）和氮（Z = 7）。尽管它们并肩排列，但三种元素在电子排布、化学键和化学行为上展现出极其规律、优美的递变——这正是考官最热衷考查的内容。

1. Atomic Number: The Identity Card | 原子序数：元素的身份证

The atomic number (Z) is the number of protons in the nucleus of an atom. Because atoms are electrically neutral, the number of electrons in a neutral atom is exactly equal to the number of protons. For example, a carbon nucleus contains 6 protons, so a neutral carbon atom must contain exactly 6 electrons orbiting around it. The mass number (A) is the total number of protons plus neutrons in the nucleus. If we know both A and Z, we can always work out the number of neutrons.

原子序数（Z）是原子核中的质子数。由于原子呈电中性，中性原子中的电子数恰好等于质子数。例如，碳原子核含有 6 个质子，因此一个中性的碳原子周围必然恰好围绕 6 个电子。质量数（A）是原子核中质子数与中子数之和。只要同时知道 A 和 Z，我们就能算出中子数。

Number of neutrons = Mass number (A) − Atomic number (Z)

For our three elements, this relationship gives the following picture:

对于我们的三种元素，这个关系式给出了如下的图景：

2. Boron (Z = 5): A Metalloid with 2.3 | 硼（Z = 5）：电子排布 2.3 的准金属

Boron has 5 protons and, in its most common isotope, a mass number of 11 — so it contains 6 neutrons. Its 5 electrons are arranged in two shells: the first shell holds 2 electrons and the second shell holds 3 electrons. We write this electron configuration as 2.3. This places boron in Group 13, Period 2 of the periodic table. With only 3 outer electrons, boron tends to lose or share all three when it reacts.

硼含有 5 个质子，其最常见的同位素质量数为 11，因此含有 6 个中子。它的 5 个电子分布在两个电子层中：第一层容纳 2 个电子，第二层容纳 3 个电子。我们将这种电子排布写作 2.3。这使硼位于元素周期表第二周期第 13 族。由于最外层只有 3 个电子，硼在反应中倾向于失去或共享这 3 个电子。

Boron is classified as a metalloid, meaning it shows properties intermediate between metals and non-metals. For example, it is shiny like a metal but brittle like a non-metal, and its electrical conductivity is much lower than a true metal. In IGCSE examinations, you should recognise that the boundary between metals and non-metals runs diagonally through the p-block, and boron sits exactly on that boundary.

硼被归类为准金属（类金属），这意味着它表现出介于金属与非金属之间的性质。例如，它像金属一样有光泽，但又像非金属一样脆，其导电性远低于真正的金属。在 IGCSE 考试中，你应当认识到金属与非金属的分界线斜穿 p 区，而硼恰好位于这条分界线上。

3. Carbon (Z = 6): The Backbone of Life | 碳（Z = 6）：生命的主干元素

Carbon has 6 protons and a most common mass number of 12, giving it 6 neutrons. Its electron configuration is 2.4, which places carbon in Group 14. Having exactly 4 electrons in the outermost shell is special

Published by TutorHao | IGCSE Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）