🧱 单质与化合物：一种原子还是几种🧱 Elemental Substances & Compounds: One Atom or Several
上一片，⚗️ 小烧瓶用放大镜把物质分成了"独唱"的纯净物和"合唱"的混合物。可它发现：纯净物里还有花样——有的独唱只用一位演员，有的用好几位。Last leaf, ⚗️ Little Flask split matter into "solo" pure substances and "choir" mixtures. But pure substances have another twist: some solos use one performer, others use several.
第 1 步：O₂ 和 H₂O，两种独唱Step 1: O₂ and H₂O — two kinds of solo
先对比两个熟悉的分子，看看独唱有什么不一样。Compare two familiar molecules first, and the difference shows up at once.
氧气 O₂ 由两个氧原子手拉手组成——整首歌只有"氧"一位演员，这叫单质。水 H₂O 由一个氧原子和两个氢原子组成——两位演员同台，这叫化合物。单质=同种元素组成；化合物=不同种元素化合而成。铁 Fe、氦 He 都是单质；二氧化碳 CO₂、食盐 NaCl 都是化合物。Oxygen, O₂, is two oxygen atoms holding hands — the whole song has only one performer, oxygen. That is an elemental substance. Water, H₂O, is one oxygen atom plus two hydrogen atoms — two performers on stage: a compound. One kind of element makes an elemental substance; different elements combined make a compound. Iron Fe and helium He are elemental; carbon dioxide CO₂ and table salt NaCl are compounds.
那铁块放久了会生锈——铁锈还是铁吗？And when iron sits around and rusts — is rust still iron?
第 2 步：铁锈不是铁Step 2: Rust is not iron
铁 Fe 里全是铁原子，是单质。铁生锈，是铁和氧气、水悄悄发生反应，生成了新物质——铁锈（主要成分氧化铁）。氧化铁由铁、氧两种元素组成，是化合物。所以铁锈不再是铁：元素重新组队，物质就换了身份。Iron, Fe, is all iron atoms — an elemental substance. When iron rusts, it quietly reacts with oxygen and water to form a new substance — rust (mainly iron oxide). Iron oxide is made of iron and oxygen: a compound. So rust is no longer iron: once the elements re-team, the substance changes identity.
元素们像积木——到底能拼出几种花样？Elements are like building blocks — how many ways can they snap together?
第 3 步：118 种积木，两种拼法Step 3: 118 blocks, two ways to build
全世界只有 118 种元素，像 118 块积木，拼法只有两种：同一种积木拼出的（O₂、Fe、He）叫单质；不同积木拼在一起的（H₂O、CO₂、NaCl）叫化合物。它们都只有一种物质，所以都属于纯净物——而混合物是好几件"成品"拌在一起。这下，物质的分类地图就齐了。There are only 118 elements in the world — 118 kinds of blocks, and just two ways to build: same blocks snapped together (O₂, Fe, He) make an elemental substance; different blocks joined (H₂O, CO₂, NaCl) make a compound. Each is still one single thing, so both are pure substances — while a mixture stirs several "finished works" together. The map of matter is now complete.
🎮 你来当双重分拣员（30 秒）🎮 Your turn: double sorter (30 seconds)
每张卡要过两层筛：先分纯净物 / 混合物，纯净物再分单质 / 化合物。来试试。Every card passes two sieves: first pure substance / mixture, then — if it's pure — elemental substance / compound. Try it.
一句话记住它：纯净物再分两类——同种元素组成的是单质，不同种元素化合的是化合物；铁锈是化合物，不是铁。Remember it in one line: pure substances split in two — one element makes an elemental substance, different elements combined make a compound; rust is a compound, not iron.
单质：同种元素组成（O₂、Fe、He）Elemental substance: one element only (O₂, Fe, He)化合物：不同种元素化合（H₂O、CO₂、NaCl）Compound: different elements combined (H₂O, CO₂, NaCl)铁锈主要成分是氧化铁（化合物）——铁生锈生成了新物质Rust is mainly iron oxide, a compound — a new substance formed from iron
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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