📚 The Periodic Table | 元素周期表
The periodic table is the single most important framework in chemistry, organising all known elements by their atomic number and revealing recurring patterns in their physical and chemical properties. It allows chemists to predict behaviour, understand bonding and design new materials.
元素周期表是化学中最重要的框架，它按原子序数编排所有已知元素，揭示了它们物理和化学性质的周期性规律。它使化学家能够预测行为、理解成键并设计新材料。
1. Development of the Periodic Table | 元素周期表的发展
Before the modern table, Johann Dobereiner grouped elements into triads with similar properties, and John Newlands proposed the Law of Octaves, noticing that every eighth element resembled the first. However, these early schemes were incomplete.
在现代周期表之前，约翰·德贝莱纳将元素按相似性质分成三元组，约翰·纽兰兹提出八音律，注意到每第八个元素与第一个相似。但这些早期方案并不完整。
Dmitri Mendeleev, in 1869, arranged elements by increasing atomic mass and placed those with similar chemical properties in vertical columns. He boldly left gaps for undiscovered elements, such as eka-aluminium (gallium) and eka-silicon (germanium), and even predicted their properties.
德米特里·门捷列夫于1869年按原子质量递增的顺序排列元素，并将化学性质相似的元素放在同一纵列中。他大胆地为未发现的元素留出空位，例如类铝（镓）和类硅（锗），甚至预测了它们的性质。
Mendeleev's genius was recognised when these predictions proved correct; however, his table had inconsistencies because ordering by mass placed tellurium before iodine despite iodine having a smaller atomic mass. The modern table is ordered by atomic number, not mass, which resolved these problems.
当这些预测被证实正确时，门捷列夫的天才得到了认可；但他的表存在不一致，因为按质量排序会让碲排在碘之前，尽管碘的原子质量更小。现代周期表按原子序数而非质量排序，解决了这些问题。
2. Structure of the Modern Periodic Table | 现代周期表的结构
The modern periodic table arranges elements in order of increasing atomic number (Z). Horizontal rows are called periods and vertical columns are called groups. There are seven periods; period 1 has only two elements, while periods 6 and 7 each contain 32 elements due to the filling of f-orbitals.
现代周期表按原子序数（Z）递增的顺序排列元素。横行称为周期，纵列称为族。共有七个周期；第1周期只有两种元素，而第6和第7周期由于f轨道的填充各有32种元素。
Groups are numbered 1 to 18 according to the IUPAC system. Previously, groups were labelled with Roman numerals and letters (e.g. IA, IIA, VIIA, VIII). The s-block consists of groups 1 and 2 plus helium; the p-block spans groups 13 to 18; the d-block contains transition metals in groups 3–12; and the f-block houses the lanthanides and actinides.
根据IUPAC体系，族编号为1至18。此前，族用罗马数字和字母标记（如IA、IIA、VIIA、VIII）。s区包括第1和第2族以及氦；p区覆盖第13至18族；d区包含第3至12族的过渡金属；f区容纳镧系和锕系元素。
A diagonal staircase line separates metals (on the left) from non-metals (on the right); elements bordering this line, such as silicon and germanium, are metalloids with intermediate properties.
一条对角线阶梯线将金属（左）与非金属（右）分开；靠近此线的元素如硅和锗是性质介于中间的类金属。
3. Electronic Configuration and the Table | 电子排布与周期表
The position of an element in the periodic table directly reflects its ground-state electronic
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