📚 IGCSE Chemistry Unit Test: Atomic Structure & The Periodic Table | IGCSE 化学单元测试卷：原子结构与元素周期表
This Unit Test is designed to help IGCSE Chemistry students assess their understanding of atomic structure and the periodic table. It includes multiple-choice questions, structured questions, a calculation and a completion task. Work through each question carefully, then check the detailed explanations and answers provided. Use this resource to identify areas for revision before your real exam.
这份单元测试卷旨在帮助 IGCSE 化学学生评估他们对原子结构和元素周期表的理解。测试包括选择题、结构化问题、计算题和填表题。仔细完成每道题，然后查看提供的详细解释和答案。利用这份资源找出需要复习的薄弱环节，为真正的考试做好准备。
1. Multiple Choice – Subatomic Particles | 选择题 – 亚原子粒子
An atom of element X has an atomic number of 19 and a mass number of 39. How many neutrons are there in one atom of X?
A 19
B 20
C 39
D 58
一个 X 元素的原子序数为 19，质量数为 39。一个 X 原子中有多少个中子？
A 19
B 20
C 39
D 58
Answer: B c number gives the number of protons, not neutrons. Option A is the proton number, C is the mass number, and D is the sum of protons and mass number, which is incorrect.
答案：B。中子数 = 质量数 − 原子序数 = 39 − 19 = 20。原子序数表示质子数，并非中子数。选项 A 是质子数，C 是质量数，D 是质子数与质量数之和，均是错误的理解。
2. Multiple Choice – Isotopes | 选择题 – 同位素
Which statement correctly describes isotopes?
A Atoms of the same element with different numbers of protons.
B Atoms of different elements with the same number of neutrons.
C Atoms of the same element with different numbers of neutrons.
D Atoms of different elements with the same mass number.
哪一项正确地描述了同位素？
A 同一种元素中质子数不同的原子。
B 不同元素中中子数相同的原子。
C 同一种元素中中子数不同的原子。
D 不同元素中质量数相同的原子。
Answer: C. Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons, leading to different mass numbers. Option A is wrong because the number of protons defines the element; B and D do not define isotopes.
答案：C。同位素是质子数相同（属于同种元素）但中子数不同的原子，因此质量数不同。选项 A 错误，因为质子数决定了元素种类；B 和 D 都不能准确地定义同位素。
3. Multiple Choice – Electronic Configuration & Groups | 选择题 – 电子排布与族
An element has the electronic configuration 2,8,2. In which group of the periodic table is it found?
A Group I
B Group II
C Group VIII
D Group 0
某元素的电子排布为 2,8,2。它位于元素周期表的哪一个族？
A I 族
B II 族
C VIII 族
D 0 族
Answer: B. The number of electrons in the outer shell is 2. Elements with 2 outer-shell electrons belong to Group II. Group I has 1 outer electron, Group VIII is a transition metal group with variable outer shells, and Group 0 (noble gases) has a full outer shell.
答案：B。最外层电子数为 2。最外层有 2 个电子的元素属于 II 族。I 族元素最外层有 1 个电子，VIII 族是过渡金属，最外层电子数不固定，而 0 族（稀有气体）的最外层为全满状态。
4. Multiple Choice – Periodic Trends | 选择题 – 周期律趋势
As you go down Group I (the alkali metals), what happens to the reactivity?
A It decreases because the outer electron is closer to the nucleus.
B It stays the same.
C It increases because the outer electron is more easily lost.
D It increases because the atomic radius decreases.
沿着 I 族（碱金属）从上往下，反应性会怎样变化？
A 反应性减弱，因为最外层电子离核更近。
B 反应性保持不变。
C 反应性增强，因为最外层电子更容易失去。
D 反应性增强，因为原子半径减小。
Answer: C. Reactivity increases down Group I because the outer electron is further from the nucleus, the shielding effect increases, and the electron is more easily lost. Atomic radius actually increases down the group, so D is incorrect.
答案：C。I 族从上往下反应性增强，因为最外层电子离核更远，屏蔽效应增强，电子更容易失去。实际上原子半径是增大的，因此选项 D 错误。
5. Structured Question – Sodium Atom & Ion | 结构化问题 – 钠原子与离子
Sodium (Na) has an atomic number of 11.
(a) Draw the electronic structure of a sodium atom, showing all shells and electrons.
(b) Explain what happens to the electronic structure when a sodium atom forms a sodium ion, Na⁺.
钠 (Na) 的原子序数为 11。
(a) 画出钠原子的电子结构，需显示所有电子层和电子。
(b) 解释当钠原子形成钠离子 Na⁺ 时，其电子结构会发生什么变化。
Answer (a): The electronic configuration of a sodium atom is 2,8,1. The first shell contains 2 electrons, the second shell 8 electrons, and the third shell 1 electron. You would draw a nucleus with 11 protons, first circle with 2 dots, second circle with 8 dots, third circle with 1 dot.
答案 (a)：钠原子的电子排布为 2,8,1。第一电子层有 2 个电子，第二电子层有 8 个电子，第三电子层有 1 个电子。画图时需画出含有 11 个质子的原子核，第一层画 2 个点，第二层画 8 个点，第三层画 1 个点。
Answer (b): The sodium atom loses its single outer electron to achieve a full outer shell (the original second shell becomes the outer shell with 8 electrons). The resulting Na⁺ ion has the electronic configuration 2,8. The ion has a +1 charge because it now has 11 protons but only 10 electrons.
答案 (b)：钠原子失去唯一的那个最外层电子，从而获得全满的最外层结构（原来的第二电子层变成了最外层，拥有 8 个电子）。形成的 Na⁺ 离子的电子排布为 2,8。该离子带 +1 电荷，因为它有 11 个质子，但只有 10 个电子。
6. Structured Question – Stability of Chloride Ion | 结构化问题 – 氯离子的稳定性
A chlorine atom gains one electron to form a chloride ion, Cl⁻. Explain, in terms of electronic structure, why the chloride ion is more stable than a chlorine atom.
氯原子获得一个电子形成氯离子 Cl⁻。请从电子结构的角度解释，为什么氯离子比氯原子更稳定。
Answer: A chlorine atom has the electronic configuration 2,8,7. Its outer shell is not full. By gaining one electron, it becomes a chloride ion with configuration 2,8,8, which is the same electronic structure as the noble gas argon. Having a full outer shell of 8 electrons makes the ion very stable, similar to the electronic arrangement of noble gases. The atom achieves a lower energy state by completing its octet.
答案：氯原子的电子排布为 2,8,7，最外层未满。获得一个电子后，氯离子具有 2,8,8 的排布，这与稀有气体氩的电子结构相同。拥有 8 个电子的全满最外层使离子非常稳定，类似于稀有气体的电子排布。通过达成八隅体，氯原子达到了能量更低、更稳定的状态。
7. Calculation – Relative Atomic Mass | 计算题 – 相对原子质量
Chlorine has two naturally occurring isotopes: ³⁵Cl with an abundance of 75% and ³⁷Cl with an abundance of 25%. Calculate the relative atomic mass (Aᵣ) of chlorine to one decimal place. Show your working.
氯有两种天然同位素：³⁵Cl 的丰度为 75%，³⁷Cl 的丰度为 25%。计算氯的相对原子质量 (Aᵣ)，结果保留一位小数。请写出计算过程。
Answer: Aᵣ = [(mass of isotope 1 × abundance) + (mass of isotope 2 × abundance)] / 100
Aᵣ = [(35 × 75) + (37 × 25)] / 100
Aᵣ = (2625 + 925) / 100
Aᵣ = 3550 / 100 = 35.5
So the relative atomic mass of chlorine is 35.5. This value appears on the periodic table as it accounts for the weighted average of the isotopes.
答案：Aᵣ = [(同位素1质量 × 丰度) + (同位素2质量 × 丰度)] / 100
Aᵣ = [(35 × 75) + (37 × 25)] / 100
Aᵣ = (2625 + 925) / 100
Aᵣ = 3550 / 100 = 35.5
因此氯的相对原子质量为 35.5。这个数值你会在元素周期表中看到，因为它包含了同位素的加权平均值。
8. Completion Table – Nuclear Symbols | 填表题 – 核符号
Complete the table below by writing the correct nuclear symbol for each particle. The first one has been done for you as an example.
完成下表中的每一个粒子，写出正确的核符号。第一个已经作为例子为你填写好了。
| Particle | Protons | Neutrons | Electrons | Nuclear Symbol |
|---|---|---|---|---|
| A | 11 | 12 | 11 | ²³₁₁Na |
| B | 17 | 18 | 18 | |
| C | 8 | 8 | 10 | |
| D | 6 | 6 | 6 |
Answers:
₇Cl⁻ (The mass number is 17+18=35; it has one more electron than protons, so a 1− charge.)
C: ¹⁶₈O²⁻ (Mass number 8+8=16; it has two extra electrons, giving a 2− charge.)
D: ¹²₆C (Carbon-12 atom, neutral.)
答案：
B：³⁵₁₇Cl⁻（质量数为 17+18=35；电子比质子多 1 个，因此带 1− 电荷。）
C：¹⁶₈O²⁻（质量数为 8+8=16；多余 2 个电子，带 2− 电荷。）
D：¹²₆C（碳-12 原子，电中性。）
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