The Bohr Model

A Problem with the Nuclear Model

• Atoms are stable; they don't collapse

• Atoms do not emit light most of the time

• When atoms do emit energy, it consists of only specific colors

Emission Spectra and the Bohr Model

• Bohr interpreted these problems and created a new model of the atom

• Bohr proposed that n defined "permitted" electron orbits around the nucleus. 

  • orbits get much larger as n increases

• He proposed that electrons would not radiate energy while traveling in a permitted orbit.

Emission Spectra and Energy Levels

• He proposed that electrons would radiate (or absorb) energy when they move between permitted orbitals.

  • Each orbital represents a different energy level

Emission Spectra and the Bohr Model 2

• Since the emission spectrum of each element is unique, it can be used to identify the presence of a particular element. 

Absorption Spectra and the Bohr Model

• When an electron is excited, it moves from a lower energy level to a higher one.

• The same energy that is released when an electron drops to a lower energy level, is required to take it up to that level.

Energy Levels

• The "ground state" of an atom is its lowest energy level, when n = 1. We can call that energy level E₁

• Then E₂ will be the energy when n = 2

• the energy of E_n is given by: 𝐸𝑛=𝐸1/𝑛2