How Electrons Move Through Energy Levels

In 1897, J.J. Thomson pictured atoms as spheres with scattered electrons. By 1911, Ernest Rutherford discovered the nucleus but couldn’t explain the electrons’ arrangement around it.

In 1913, Niels Bohr proposed that the electrons orbit the nucleus at fixed distances based on their energy. These fixed distances, called energy levels, are like steps on a staircase.

Electrons can only "stand" on specific steps, with closer steps having lower energy and farther ones having higher energy. To explain how electrons move between these levels, Bohr introduced the concept of 'quantum'—the smallest packet of energy.

Think of a vending machine: you can’t use any random amount of money but must insert exact coins.

Similarly, electrons only move to a higher energy level when they absorb a fixed amount of energy called a quantum, equal to the energy difference between levels.

If an electron absorbs this exact energy, it jumps to a higher level, and releasing the same amount of energy allows it to return to its original level.

Bohr was awarded the Nobel Prize in Physics for this groundbreaking theory in 1922.