An element is a pure substance made of only one type of atom. Its particles can be single atoms (helium) or atoms joined together (O₂), but every atom is the same type. Each element has a symbol of one or two letters, and the periodic table lists them all.
Everything around you, from your phone to your fingernails, is built from fewer than a hundred kinds of atom. Each kind is an element.
Last lesson: atoms come in types. This lesson: substances made of just one type.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: pure oxygen, pure water
ExploreTry it on the board and compare what happens with your prediction.
Explore: one type of atom?
Click a particle, or press Inspect next particle, to see which atoms it is made of.
The board names each kind of particle: element or compound.
Try it yourselfNothing is saved: start again as often as you like.
Inspect the particles in pure oxygen.
Use the board. This ticks when you get there.
Now inspect pure water vapour.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: elements and symbols
In your book: draw particles of an element made of single atoms, an element made of pairs of atoms, and a compound. Label each, and write the symbols you used.
Element or compound?
O₂ (oxygen)
He (helium)
N₂ (nitrogen)
O₃ (ozone)Three oxygen atoms: still one type.
H₂O (water)
CO₂ (carbon dioxide)
NaCl (salt)
Match each symbol to its element.
O
C
Fe
Na
Cu
Au
Elaborate TypicalUse the same idea in a new context.
Elaborate: Co or CO?
Try it yourselfNothing is saved: start again as often as you like.
Inspect the particles of CO.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: two forms of oxygen
Try it yourselfNothing is saved: start again as often as you like.
Inspect both kinds of particle.
Use the board. This ticks when you get there.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
An element is a pure substance made of only one type of atom. Its particles can be single atoms (He) or atoms joined together (O₂, O₃).
A compound has two or more types of atom joined (H₂O, CO₂).
Each element has a symbol: one capital letter, or a capital and a small letter (C, Co, Na). Some come from Latin names (Fe, Na, Cu, Au).
The periodic table lists all the elements, about 118.
For teachers
Students define an element as a pure substance of only one type of atom, tell elements from compounds by their particles, and use chemical symbols (AC9S8U06, node 2). About 24 minutes.
I can tell an element from a compound by the atoms in its particles.
I can use chemical symbols, including two-letter ones.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It builds on What are particles made of? (node 1) and comes before Why isn't salt poisonous? (compounds, node 3).
Not a hinge node, but two ideas trip students up here: "pure" taken to mean "element", and "element" taken to mean "single atoms" (so O₂ looks like a compound). The prediction tests both.
Board notes: every substance is drawn as a gas in a box, including metals' atoms in other lessons; real metals are solids made of atoms packed together. Molecules are rigid, in 2D. The board names each kind of particle (element or compound) once inspected.
Running the lesson
Engage: tally the predictions. 'Both' means pure = element; 'neither' means element = single atoms.
Explore: ask what was the same about every atom in the oxygen jar, and what was different in water.
Explain: the definition, the sort and the symbols are the node's success criteria; Co and CO is the two-letter rule.
In your own words: the three labelled particle drawings are the evidence.
The hard part (on purpose)
Elements made of joined atoms (O₂). Ask 'how many types of atom?' rather than 'how many atoms?', and let the student recount.
When students get stuck
A student says oxygen is a compound because each particle has two atoms. Ask: Are the two atoms the same type or different? Fix: The same: both oxygen. One type of atom makes it an element, however many are joined.
A student says water is an element because it is pure. Ask: How many types of atom are in a water particle? Fix: Two, hydrogen and oxygen: a pure compound. Pure means one substance, not one type of atom.
A student writes CO for cobalt. Ask: How many capital letters are in CO? Fix: Two, so two elements: carbon and oxygen. Cobalt is Co, a capital and a small letter.
Stretch and support
Stretch: Diamond and graphite are both pure carbon. Why are they so different? (The carbon atoms are joined in different patterns.)
Support: Give the frame: 'Every atom in … is …, so it is an element.' and 'A … particle has … and … atoms, so it is a compound.'
Where it leads
Next: Why isn't salt poisonous? (compounds, node 3).
In class: element samples (copper, sulfur, carbon, aluminium foil) beside compounds (salt, water, sugar); a periodic table hunt for the elements in everyday objects; symbol bingo.
What each step is for
Engage: pure oxygen, pure water: Students often think 'pure' means 'element', or that an element's particles must be single atoms; the options separate both ideas.
Explore: one type of atom?: Inspecting the particles of two pure substances side by side makes 'one type of atom' the test, not 'pure' or 'single atoms'.
Explain: elements and symbols: Defining an element by atom type, then using symbols and their two-letter rule, sets up formulas for compounds next lesson.
Elaborate: Co or CO?: Inspecting carbon monoxide makes the capital-letter rule concrete: two capitals, two elements, a compound.
Elaborate: two forms of oxygen: Ozone and oxygen are the same element in two forms, which breaks the idea that one element means one substance.
Now you can
Define an element.
Tell an element from a compound by the atoms in its particles.