Glossary term: 原子
Description: 原子是构成任何化学元素的最小基本单元。例如，氦气由许多氦原子组成，每个氦原子彼此无异；碳元素（如钻石形式）则是碳原子的集合。
“原子”一词源于古希腊哲学家德谟克利特，他认为原子是不可分割的物质基本组成部分。然而，根据现代定义，原子由电子、质子和中子构成。质子和中子构成原子核，所有给定化学元素的原子都具有相同数量的质子，是该元素的唯一特性。原子核被电子包围。通常所说的原子是电中性的，质子带有单位正电荷，电子带有单位负电荷，两者数量相等。当电子从中性原子中被移除或被添加到中性原子时，原子则会变为离子。
电子层决定了原子的化学性质。不同种类原子的差异和相似性在元素周期表中被系统地组织和分类。电子层也决定了原子与辐射相互作用的方式。通过分析接收到的来自天体的光谱特征，天文学家可以区分太空中存在的不同种类原子。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
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