Electron configuration shows how electrons are arranged in shells around the nucleus.
In a neutral atom, electrons = atomic number. Fill the innermost shell first.
First shell: up to 2 electrons.
Second shell: up to 8 electrons.
For the first 20 elements: put up to 8 in the third shell, then start the fourth.
Oxygen has 8 electrons: 2 in the first shell and 6 in the second. Write this as 2,6.
Sodium’s configuration is 2,8,1. Check: 2 + 8 + 1 = 11.
The outer shell is the occupied shell furthest from the nucleus. Sodium has 1 outer electron.
For these elements, the fourth shell starts after 2,8,8.
Potassium (19): 2,8,8,1.
Calcium (20): 2,8,8,2.
These are simplified shell diagrams, not to scale. Dots represent electrons.
Count: electrons = atomic number.
Fill: start with the innermost shell.
Check: add the shell numbers to find the total electrons.
Count the dots. Fill the shells.
Dots are electrons. Start at the inner shell.
One point for each answer you get right first time.
No timer. Take your time and use a clue whenever you need one.