Video narration
Remembering where the electrons go can feel like memorising twenty separate facts. Instead, picture students filling rows of seats. For a neutral atom, its atomic number tells you how many students-or electrons-it has. Fill the first row, the first electron shell, with up to two; then the next with up to eight, and the third with up to eight. In this simplified model, go in order. So the first twenty build step by step: hydrogen 1; helium 2; lithium 2,1; beryllium 2,2; boron 2,3; carbon 2,4; nitrogen 2,5; oxygen 2,6; fluorine 2,7; neon 2,8. Then sodium 2,8,1 through argon 2,8,8, adding one each time. Finally, potassium is 2,8,8,1, and calcium is 2,8,8,2. The shortcut is simple: start with the atomic number, fill 2, then 8, then 8, and begin the fourth shell. One pattern places all twenty.