Chemistry 06202.2 Atomic structure and the Periodic Table
Electron shells
Build any of the first 20 atoms and see its electronic configuration, group and period appear.
- Electronic configuration
- Group and period
- Shell capacities 2, 8, 8, 2
Protons
11
Electrons
11
Group
I
Period
3
Predict
An atom has the configuration 2,8,7. Which group is it in?
Experiment
- 1Set Z to 11, then 12, then 13 and watch the outer shell fill one electron at a time.
- 2Compare Z = 2, 10 and 18. What do their outer shells have in common?
- 3Find every element whose outer shell holds exactly one electron.
Explain
Electrons occupy shells filling from the inside out, with capacities 2, 8, 8, 2 across the first 20 elements.
The number of outer-shell electrons equals the group number (for Groups I–VII) and the number of occupied shells equals the period number. That single rule lets you place any of the first 20 elements without memorising the table.
Atoms react to reach a full outer shell. Metals with few outer electrons lose them; non-metals with nearly full shells gain or share. Every bonding topic follows from this.