Students explain that a new period begins when a new shell starts filling, that properties repeat because outer-electron counts repeat, and read an element's shells from its period and group (AC9S10U06, node 3).
Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.
Engage and Explore 8 min · Explain 10 min · Evaluate 3 min · Typical adds 4 min, Wider about 4 min
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It builds on Shells and Groups (nodes 1 and 2).
Not a hinge node: it pulls shells and groups together into the table's shape. The prediction catches students who expect outer electrons to keep counting up (sodium with 9).
Board notes: the table shows elements 1 to 20 only, in groups 1, 2 and 13 to 18 (transition metals start in period 4, after calcium). Colour by outer electrons counts helium's 2 as a full shell (with the noble gases). The metalloids shown are boron and silicon. Shells fill 2, 8, 8, 2 for these elements; the 8 in the third shell is a simplification that stops working after calcium.
Seeing why the count resets. Ask how many electrons fit in the shell before you tell them; let them find that sodium needs a new one.
| What you will see | A question to ask | The fix |
|---|---|---|
| A student thinks sodium has 9 outer electrons. | How many electrons fit in the second shell? | 8. It is full at neon, so sodium's last electron starts a third shell: 2, 8, 1. |
| A student mixes up periods and groups. | Which way do rows go, and what do they share? | A period is a row: same number of shells. A group is a column: same number of outer electrons. |
| A student thinks the table is ordered by mass. | What goes up by exactly 1 each step along the table? | The atomic number (protons, and electrons in a neutral atom). Mass mostly rises too, but not always in step (argon is heavier than potassium). |
One possible solution for each task. Other correct programs are fine.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Stretch: Argon (atomic number 18) has a larger relative atomic mass than potassium (19). If Mendeleev had ordered strictly by mass, what would have gone wrong? (Argon would land in group 1 and potassium in group 18: the reverse of how they behave.)
Support: Give the frame: 'Period = number of … . Group = number of … electrons. So an element in period … and group … has shells … .'
For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.
You are a patient science coach for a Year 10 student in Australia. Help me understand ONE idea only, from the lesson "Why does the periodic table repeat?". The idea: Periodic trends — why properties repeat across periods: I can describe repeating patterns of properties across the periodic table and explain them as a consequence of repeating outer electron shell configurations. What understanding looks like: - Explains that a new period begins when electrons start filling a new shell - Describes that properties repeat across periods because outer electron configurations repeat - Interprets the position of an element in the table in terms of its electron shell configuration Mistakes students often make here: - A student thinks sodium has 9 outer electrons. - A student mixes up periods and groups. - A student thinks the table is ordered by mass. How to coach me (rules from the Waypoints Kit coach): - Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question. - Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit). - If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go. - If I seem to be missing the idea that comes before this one (Outer electrons and group properties — why elements in a group behave similarly), check it quickly, then come back. - Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back. - After you help, ask me one reflective question, such as how I know my answer is right or what I would check. - Praise my effort and method, not my ability. - You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so. - Use simple words. - Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "Why does the periodic table repeat?".
Element X has electrons 2, 8, 3. Which period and group is it in, and is it more likely a metal or a non-metal?
Period 3 (three shells), group 13 (three outer electrons): aluminium, a metal.
Next: node 4 (predicting and explaining an element's properties from its structure) is a class task: give students unfamiliar elements in groups 1, 2, 17 and 18 and ask them to predict reactions.
In class: element cards sorted into a table without labels; Mendeleev's predictions for eka-silicon against germanium's measured properties.