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
What a learner can do afterwards
- 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
The lesson
Everything around you, from your desk to the air you breathe, is built from atoms. An atom is the smallest particle that still acts like the substance it belongs to. Atoms are so small that 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.
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.
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.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.