--- title: "Atoms, Elements & Compounds" description: "Explain the differences between atoms, elements, and compounds; describe the simple Bohr model of the atom (nucleus with protons and neutrons, electrons in shells); and write and interpret chemical sy" canonical: https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI source: https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Atoms, Elements & Compounds Explain the differences between atoms, elements, and compounds; describe the simple Bohr model of the atom (nucleus with protons and neutrons, electrons in shells); and write and interpret chemical symbols and simple formulae Subject: Science · Area: Matter & Materials · Ages 11 to 12 Page: https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI ## Ready when they can - Defines atom, element, and compound and distinguishes between them with examples - Draws a simple Bohr model of an atom labelling nucleus (protons/neutrons) and electron shells - Reads a chemical formula to identify the elements and number of each atom (e.g. H₂O, CO₂, NaCl) - Identifies the difference between a mixture and a compound ## Lesson: Atoms, Elements & Compounds You already know solids, liquids and gases are made of tiny moving particles. Those particles include atoms. An atom is the smallest unit of an element that still acts like that element. Billions of them would fit on the head of a pin. An element is a substance made of only one kind of atom. Oxygen gas is an element because every atom in it is an oxygen atom. Scientists know about 118 elements, and each one has its own chemical symbol, like O for oxygen or Na for sodium. In a simple Bohr picture, protons and neutrons pack in the centre, called the nucleus, and electrons move around it in shells. *(drawing: This carbon-12 atom has 6 protons and 6 neutrons in its nucleus and 6 electrons in shells around it. The bars count each kind.)* **Example.** Water is a compound, not an element. Each molecule links two hydrogen atoms to one oxygen atom. If you saw the formula H₂O on a label, you'd know exactly what's inside: H for hydrogen, O for oxygen, and the small 2 showing two hydrogen atoms for every one oxygen atom. Don't mix up a compound with a mixture. In a compound like water, the atoms are chemically joined and can't be pulled apart by simple means. In a mixture, like a bag of trail mix, the different bits just sit side by side, so you can still pick them apart. **Recap.** Atoms make up elements, elements can join to form compounds, and a formula like H₂O tells you exactly which atoms, and how many, are inside. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Particle Model](https://lightmysky.com/learn/science/the-particle-model-mt_b6kZgqolEd) ## Opens up - [Physical vs Chemical Changes](https://lightmysky.com/learn/science/physical-vs-chemical-changes-mt_1hgck6ucII) - [Acids, Alkalis & pH](https://lightmysky.com/learn/science/acids-alkalis-and-ph-mt_AN2kJE6I0s) - [Inside the Atom: the Nuclear Model](https://lightmysky.com/learn/science/inside-the-atom-the-nuclear-model-mt_B_PtnvyRIo) - [Radiometric Dating](https://lightmysky.com/learn/science/radiometric-dating-mt_bHbpLW1HUg) - [Where Elements Come From](https://lightmysky.com/learn/science/where-elements-come-from-mt_KYx0m4OyZv) - [Pure Substances & Mixtures](https://lightmysky.com/learn/science/pure-substances-and-mixtures-mt_MBTVB-E-S7) - [The Periodic Table](https://lightmysky.com/learn/science/the-periodic-table-mt_wfEfQuHOG-) - [Inside the Atom: Protons, Neutrons and Electrons](https://lightmysky.com/learn/science/inside-the-atom-protons-neutrons-and-electrons-mt_WqDXAr2IkA)