Isotopes | 同位素

📚 Isotopes | 同位素

Isotopes are atoms of the same element with the same atomic number but different mass numbers. This means they contain identical numbers of protons but different numbers of neutrons. Understanding isotopes is fundamental in A-Level Chemistry because it explains non-integer relative atomic masses, mass spectrometry data, and the special properties of radioisotopes.

同位素是同一元素具有相同原子序数但不同质量数的原子。这意味着它们含有相同数目的质子，但中子数不同。理解同位素是 A-Level 化学的基础内容，因为它解释了非整数相对原子质量、质谱数据以及放射性同位素的特殊性质。

1. Defining Isotopes | 同位素定义

Isotopes are atoms of the same element that have the same atomic number, Z, but different mass numbers, A. Since Z is the number of protons, isotopes contain exactly the same number of protons; since A is the total number of protons and neutrons, isotopes differ in their number of neutrons.

同位素是同一元素具有相同原子序数 Z 但不同质量数 A 的原子。由于 Z 是质子数，同位素含有完全相同的质子数；而由于 A 是质子数与中子数之和，同位素的中子数不同。

A common example is carbon: carbon-12 has 6 protons and 6 neutrons, carbon-13 has 6 protons and 7 neutrons, and carbon-14 has 6 protons and 8 neutrons. All three are carbon because Z = 6, but their mass numbers are 12, 13, and 14.

一个常见例子是碳：碳-12 有 6 个质子和 6 个中子，碳-13 有 6 个质子和 7 个中子，碳-14 有 6 个质子和 8 个中子。这三种原子都是碳，因为 Z = 6，但它们的质量数分别是 12、13 和 14。

2. Nuclide Notation | 核素符号表示法

Isotopes are represented using nuclide notation. The mass number A is written as a superscript on the left, the atomic number Z is written as a subscript on the left, and the element symbol follows. For example, carbon-14 is written as ¹⁴₆C and uranium-235 as ²³⁵₉₂U.

同位素用核素符号表示。质量数 A 写在左上角，原子序数 Z 写在左下角，随后是元素符号。例如，碳-14 写为 ¹⁴₆C，铀-235 写为 ²³⁵₉₂U。

From the notation, the number of neutrons is calculated as A − Z. For ²³⁵₉₂U, the number of neutrons is 235 − 92 = 143. For a neutral atom, the number of electrons equals Z, so isotopes of the same element also have the same number of electrons.

根据符号，中子数等于 A − Z。对于 ²³⁵₉₂U，中子数为 235 − 92 = 143。对于中性原子，电子数等于 Z，因此同一元素的同位素也具有相同的电子数。

3. Isotopes of Hydrogen | 氢的同位素

Hydrogen has three naturally important isotopes: protium ¹H, deuterium ²H, and tritium ³H. Protium has 1 proton and 0 neutrons, deuterium has 1 proton and 1 neutron, and tritium has 1 proton and 2 neutrons.

氢有三种重要的同位素：氕 ¹H、氘 ²H 和氚 ³H。氕有 1 个质子和 0 个中子，氘有 1 个质子和 1 个中子，氚有 1 个质子和 2 个中子。

Deuterium is sometimes given the symbol D, and tritium the symbol T. Ordinary hydrogen gas consists almost entirely of ¹H₂, while deuterium forms ²H₂O, often called heavy water. Tritium is radioactive and decays by beta emission with a half-life of about 12.3 years.

氘有时用符号 D 表示，氚用 T 表示。普通氢气几乎全部由 ¹H₂ 组成，而氘可形成 ²H₂O，通常称为重水。氚具有放射性，通过 β 发射衰变，半衰期约为 12.3 年。

4. Chemical and Physical Properties | 化学性质与物理性质

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