📚 Structure of the Periodic Table | 元素周期表的结构
The periodic table is the single most important organisational tool in chemistry. It arranges all known elements in order of increasing atomic number and groups them according to repeating patterns in their electron configurations. Understanding its structure allows chemists to explain and predict the physical and chemical behaviour of elements and their compounds.
元素周期表是化学中最重要的组织工具。它按原子序数递增的顺序排列所有已知元素，并根据其电子排布的重复规律将它们分组。理解周期表的结构有助于化学家解释和预测元素及其化合物的物理和化学行为。
1. The Periodic Law and Atomic Number | 周期律与原子序数
The modern periodic table is based on the periodic law, which states that the properties of elements are a periodic function of their atomic number. This replaced Mendeleev's original arrangement by relative atomic mass, which caused several elements to be misplaced.
现代周期表以周期律为基础，周期律指出元素的性质是其原子序数的周期性函数。这取代了门捷列夫最初按相对原子质量排列的方法，该方法曾导致若干元素位置错误。
Atomic number, Z, is the number of protons in the nucleus of an atom. Because a neutral atom has the same number of electrons as protons, the atomic number also determines the electronic structure that governs chemical reactivity.
原子序数 Z 是原子核中的质子数。由于中性原子的电子数与质子数相同，原子序数也决定了支配化学反应活性的电子结构。
The table groups elements with similar outer-shell electron configurations in vertical columns, while horizontal rows show the progressive filling of successive electron shells.
周期表将具有相似外层电子排布的元素排在同一纵列，而横行则显示电子壳层逐级填充的过程。
2. Periods: Horizontal Rows | 周期：横行
A period is a horizontal row of the periodic table. Moving from left to right across a period, each successive element has one more proton and one more electron than the previous element.
周期是周期表的横排。沿着周期从左到右，每一个后续元素比前一个元素多一个质子和一个电子。
example, elements in Period 2 have their outermost electrons in the second shell (n = 2).
周期序数表示元素基态中占据的最高主量子数 n。例如，第 2 周期的元素其最外层电子位于第二壳层（n = 2）。
There are seven periods in the standard table. Period 1 contains only hydrogen and helium, while Periods 2 and 3 contain eight elements each, and later periods contain transition elements and inner transition elements.
标准周期表共有七个周期。第 1 周期仅包含氢和氦，第 2 和第 3 周期各有八种元素，后面的周期则包含过渡元素和内过渡元素。
3. Groups: Vertical Columns | 族：纵列
A group is a vertical column of the periodic table. Elements in the same group have the same number of electrons in their outermost shell, so they typically show similar chemical properties.
族是周期表的纵列。同一族的元素最外层电子数相同，因此它们通常表现出相似的化学性质。
For Groups 1, 2 and 13 to 18, the modern group
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