Bohr’s Model of the Atom Chapter 5

The Modern View of the Atom The atom is mostly empty space. Two regions The Nucleus – Protons and neutrons are located in the nucleus. Electron cloud region – Place where you might find an electron.

The Atom is mostly empty space From his measurements, Rutherford estimated the radius of an atom to be 100,000 times greater than the radius of the nucleus. This is comparable to the thickness of a dime to the length of football field

Max Planck’s Quantum Theory What did Planck proposed? Quanta = plural Quantum = singular Atom energy is absorbed or liberated in packets or chunks of energy. Planck called these packages of energy "quanta".

Photon The Quantum of Light = the Photon. Particles of light are called light quanta or photons. Energy of a Photon = h x u E = h x u or E = h x f h is Planck’s constant h = 6.63 x 10-34 J.s u is equal to the frequency of light. u = f = frequency

Packet of energy in a photon is so small that we are not aware of the rain of photons of light impinging on our eyes – just as you cannot feel the impact of individual air molecules.

The quantum concept Max Planck (1900) Einstein (1905) Introduced quantized energy Einstein (1905) Light made up of quantized photons Higher frequency photons = more energetic photons

Bohr’s atomic model Niels Bohr puts it all together Bohr added Planck’s quanta idea (which was proven by Einstein and Louis de Broglie’s wave/particle theory) to the Rutherford’s atomic model.

Electrons exist at set levels of energy, at fixed distances from the nucleus. When an atom absorbs energy, the electron jumps to a level further from the nucleus If it radiated energy, that means that the electron is falling to a level closer to the nucleus.

The protons and neutrons are located in the nucleus. The electrons are located at different energy shells (energy levels around the nucleus)

Energy Levels/shells There are several energy levels in which an electron might be found. To move from one level to another an electron must gain or lose an exact amount of energy. Quantum 2nd shell 1st shell e- 2 electrons e- e-

Bohr’s T heory Three rules: Electrons only exist in certain allowed orbits Within an orbit, the electron does not radiate Radiation is emitted or absorbed when changing orbits