The Atom's Address System
📖 The Atom's Address System
Electrons fill shells like fans filling a stadium — front rows first! The closest seats to the pitch (1st shell) are expensive and limited — only 2 VIP seats. The second tier (2nd shell) has 8 seats. The third tier (3rd shell) also has 8. Nobody sits in the upper tiers until the lower ones are full. That's exactly how electrons work: they always fill the lowest energy level first before moving up.
Electrons fill shells from the lowest energy level outwards because all systems in nature move towards the lowest possible energy state — this is a fundamental principle of physics. The first shell is closest to the positively charged nucleus, so electrons there experience the strongest electrostatic attraction and sit
Earn the mark scheme marks
🧠 Memory Aids
Shell capacity: "2 then 8, 8, 8..." — The first shell is special with only 2. All subsequent shells (at GCSE) hold up to 8.
Periodic table link: "Group = Outer, Period = Shells" — Group number tells you how many electrons are on the outside; period number tells you how many shells are occupied.
Reactivity reminder: "1 outer = very reactive (Group 1), 7 outer = very reactive (Group 7), 8 outer = stable (Group 0)." The extreme groups are the most reactive; the noble gases are the most stable.
Now try it yourself
Quiz · Question 1 of 24
What is the maximum number of electrons the first electron shell can hold?
Tap an answer to check it