The Quantum Model and Electron Arrangement
Quantum theory describes electrons as existing in specific energy levels or shells around the nucleus. These shells are numbered using principal quantum numbers n=1,2,3,etc..
Lower quantum numbers mean closer to the nucleus and lower energy. As you move away from the nucleus, energy levels get closer together, explaining why larger atoms can accommodate so many electrons.
Positive ions always have higher ionisation energies than their neutral atoms because there are more protons than electrons, creating a stronger effective nuclear charge that holds remaining electrons more tightly.
Key Concept: Energy levels aren't fixed orbits like planets - they're probability zones where electrons are most likely to be found!