The periodic table is not a list to look up but a tool for prediction. An element's group gives its number of outer electrons, and so how reactive it is and what it bonds with; its period gives its number of shells. From the position alone you can predict whether an element is a metal, how it reacts and what its atom looks like.
When Mendeleev laid out the elements in 1869 he left gaps and said: an element will be found here, and it will behave like this. He was right. How could a table predict something nobody had seen?
You know shells, groups and trends. Now use the table to predict something you haven't been told.
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: a stranger in group 1
ExploreTry it on the board and compare what happens with your prediction.
Explore: read the table
Try it yourselfYour edits are saved in this browser.
Click the element in group 2, period 3. How many outer electrons does it have?
Use the board. This ticks when you get there.
Click the element in group 17 (the halogens), period 2.
Use the board. This ticks when you get there.
Click the element in group 18 (the noble gases), period 3.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: predicting
In your book: choose an element you haven't studied (such as potassium or fluorine). Write its group and period, then predict its outer electrons, shells, reactivity and the ion it forms, and say how you worked it out.
An element is in period 3, group 16. How many outer electrons does it have?
The same element is in period 3. How many electron shells does it have?
Elaborate TypicalUse the same idea in a new context.
Elaborate: a flame test
Elaborate WiderUse the same idea in a new context.
Elaborate: gaps in the table
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
The group gives the number of outer electrons; the period gives the number of shells.
Outer electrons decide reactivity and bonding: group 1 loses one electron, group 17 gains one, group 18 is stable.
Reactivity grows down group 1 and falls down group 17.
The table is a predictive model: Mendeleev's gaps predicted elements before anyone found them.
For teachers
Students use an element's position in the periodic table to predict its outer electrons, shells, reactivity and bonding, explain properties from atomic structure, and use the table as a predictive tool (AC9S10U06, node 4, an integration node). About 22 minutes.
I can predict outer electrons and shells from group and period.
I can predict reactivity and the ion an element forms.
I can explain two properties with atomic structure.
Before class
An integration tutorial that follows the trends lesson. Set the width with ?width=minimum, typical (default) or wider. The board covers elements 1 to 20, so the questions about rubidium and germanium are reasoned from the pattern rather than clicked.
The group-number shortcut (group minus 10 for outer electrons) works for groups 13 to 18 only; transition metals are left to class. Reactivity trends are given as patterns, not rules without exceptions.
Running the lesson
Engage: tally the predictions. Ask the 'look it up' group what they would be looking up.
Explore: ask how the outer electrons changed along period 3.
Explain: the outer-electron questions and the reactivity trend are the success criteria.
In your own words: the predicted properties of a new element and how they were found.
The hard part (on purpose)
Using position as the evidence. When a student asks 'is it in the book?', ask what the group tells them about its outer electrons.
When students get stuck
A student says lithium is more reactive than rubidium because it is smaller. Ask: Which outer electron is held more tightly, and why? Fix: Lithium's, because it is closer to the nucleus. Rubidium's is further away and easier to lose.
A student says sodium gains an electron. Ask: How many outer electrons does it have, and what is the easiest way to a full shell? Fix: One; losing it leaves a full shell underneath. Group 1 loses an electron.
Stretch and support
Stretch: An element is in group 2, period 6. Predict its outer electrons, its reactivity compared with magnesium, and the charge on its ion. (2; more reactive; 2+.)
Support: Give a template card: 'Group ___ means ___ outer electrons. Period ___ means ___ shells. It will (lose/gain) ___ electron(s) to form a ___ ion.'
Where it leads
Next: Year 10 reaction types and collision theory.
In class: flame tests (with school safety rules), a spectroscope for lamps of different elements, a puzzle where students place unlabelled element cards on a blank table using their properties.
What each step is for
Engage: a stranger in group 1: Students want to look up the answer. The node asks them to reason from position: group gives outer electrons, so reactivity and bonding.
Explore: read the table: Finding elements from group and period, and seeing outer electrons on the board, practises using the position as the information.
Explain: predicting: Predicting outer electrons, shells, reactivity and bonding from position, and explaining two properties from structure, meets the three success criteria.
Elaborate: a flame test: Flame tests are the classic evidence that atoms have electron shells with fixed energies.
Elaborate: gaps in the table: Mendeleev's gaps and predictions show the table working as a predictive model before atomic structure was understood.
Now you can
Predict outer electrons and shells from group and period.