Revision notes
Read the core explanations from Electron Arrangement and Energy Levels before testing yourself from memory.
1. Why Electrons Don't Just Fall Into the Nucleus
Here's something that puzzled scientists for decades: if electrons are negatively charged and the nucleus is positively charged, why don't they just crash together? The answer revolutionised our understanding of atoms.
Electrons can't exist anywhere they want around the nucleus. They're restricted to specific distances - like being forced to stand on particular rungs of a ladder, never between them. These fixed positions are called energy levels.
Think of energy levels like the floors of a building. An electron can be on the ground floor, first floor, or second floor - but never floating between floors. The ground floor (closest to nucleus) requires the least energy to reach.
2. How Electrons Jump Between Energy Levels
Electrons can move between energy levels, but only in specific ways. They need exactly the right amount of energy to make the jump - like needing the exact change for a vending machine.
When an electron absorbs electromagnetic radiation (like light), it gains energy and jumps to a higher energy level - further from the nucleus. This is called excitation. The electron has moved from a lower energy level to a higher one.
But electrons don't stay excited forever. They naturally fall back down to lower energy levels, releasing the extra energy as electromagnetic radiation. This is called emission.
3. Ground State vs Excited State
Most of the time, electrons occupy the lowest possible energy levels. This minimum-energy arrangement is called the ground state - it's the atom's natural, relaxed condition.
When energy is added, electrons can move to higher energy levels, creating an excited state. But this doesn't last - excited electrons quickly fall back down, releasing energy as light.
4. Electron Transitions and Emission
When electrons change energy levels, they absorb or emit electromagnetic radiation.
Each element has its own unique pattern of energy levels. When electrons fall from higher to lower levels, they emit specific frequencies of light. Different energy gaps produce different colours - this creates each element's unique 'fingerprint' of light.
This shows that electrons can only move between specific energy levels.
5. Common Mistakes and Exam Success
Students often get confused about the direction of energy changes. Remember: absorption means gaining energy and moving to higher levels (further from nucleus). Emission means losing energy and moving to lower levels (closer to nucleus).
Another trap: thinking electrons can exist anywhere around the nucleus. They can't - only at specific energy levels. It's like a staircase, not a ramp.