Learning objectives
Students should be able to:
-
Use atomic number to determine the number of electrons in a neutral atom.
-
Draw shell diagrams and write configurations for the first 20 elements.
-
Explain how electron arrangements relate to group and period.
-
Explain why elements in the same group have similar chemical properties.
-
Use periodic-table position to predict possible reactions and relative reactivity.
Using the lesson
-
Opening and retrieval
Introduce the objectives, then revisit atomic number and the relationship between protons and electrons in a neutral atom. Distinguish atomic number from mass number.
-
Explore shell filling
Select an element and use Play, Pause, Step, Reset or the slider to investigate filling from the innermost shell outwards. Compare sodium with potassium to show when a new shell begins.
-
Model the drawing convention
Add electrons at 12, 6, 3 and 9 o’clock, then pair them in the same order. Each pair is centred around its clock position. The first shell contains a maximum of two electrons, shown at 12 and 6. Switch between dots and crosses to demonstrate that both represent electrons.
-
Worked examples and guided practice
Model counting electrons, filling shells and writing the configuration. Use Established so far and Full workings so far to retain earlier results. Students then complete the guided steps; a correct final configuration completes the diagram before they move to independent practice.
-
Independent drawing and writing
Students select an element, build its diagram using the electron positions or +/− controls, and enter its numerical configuration. Check both provides feedback on the diagram and written answer. Encourage a paper attempt before revealing the model answer.
-
Connect to the periodic table
Select elements and highlight their group or period. Compare any two elements, using the provided examples to contrast the same group, the same period and the helium exception. Ask students to predict similarities before revealing the explanation.
-
Apply and review
Use the reaction predictions to explore Group 1, Group 7 and Group 0 patterns. Finish with misconception correction and exit questions requiring students to connect configurations, atomic numbers and periodic-table positions.
Teaching tips and common misconceptions
-
Period = number of occupied shells. For Groups 1–7, group number = number of outer-shell electrons.
-
Group 0 has a full outer shell. Helium has two outer electrons; neon and argon have eight.
-
For the first 20 elements, potassium and calcium are 2,8,8,1 and 2,8,8,2. Avoid teaching that the third shell can never hold more than eight.
-
A correct electron total is not sufficient: electrons must also occupy the appropriate shells.
-
The clock positions and pairing are drawing conventions, not fixed electron locations, literal orbits or orbital-filling rules. Diagrams are not to scale.
-
Similar outer-electron arrangements explain chemical similarities within groups. Sharing a period does not imply similar chemical properties.
-
Hydrogen is unusual and should not be treated as an alkali metal.
-
The bromine displacement question extends application beyond the first-20 drawing scope. Position supports qualitative predictions, not exact reaction rates.
Display and independent learning
Choose Teal & Cream, Ocean, Plum or Slate, and use Focus or Full screen for projection. Navigate using the section tabs, lesson selector or Previous/Next buttons.
The same lesson supports teacher-led discussion and independent practice. Encourage students to attempt answers before checking or revealing them. Written explanations remain during the open session but are not saved after reloading. The HTML works offline.
No practical activity is required; the reaction questions are prediction tasks rather than laboratory instructions.