Bohr’s Postulates
1. Negatively charged electrons orbit the nucleus
2. There are different energy levels (rings)
3. The further electrons are from the nucleus, the more energy they possess
4. Electrons can move up energy levels (further from the nucleus) by gaining energy (typically from light)
5. Electrons can move down energy levels (closer to the nucleus) by emitting energy as light
The energy level is often represented with the variable n.
Limitations
– He believed electrons orbited in definite circular paths, while they really have 3D orbits that are pretty unpredictable
– Violated Heisenberg Uncertainty Principle (discussed in “Wave-Particle Duality”)
– Essentially, he oversimplified the motion of electrons
Rydberg Equation
This equation is meant to find the change in energy as an electron travels from one energy level to another.
• ΔE is the change in energy caused by the transition
• ni is the starting energy level (before the transition)
• nf is the ending energy level (after the transition)
• -2.18 x 10⁻¹⁸ J is Rydberg’s constant
Rydberg’s equation can also be manipulated to find the energy of an electron at level n.
Here, E is not a change in energy, but the actual energy possessed by an electron at energy level n.
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