Models of the Atom

Chapter 4 Chm 1.1.2 and 1.1.3

Model: Neils Bohr

• e- circles nucleus in allowed paths, “orbits”• Each orbit has a fixed energy• e- cannot exist between energy levels• e- in orbit farther from nucleus have higher

energy• e- in orbit closest to the nucleus have

lowest energy

The Bohr Model Purpose

• To explain the hydrogen line emission spectrum

• To explain why atoms of hydrogen give off light

The Hydrogen Line Emssion Spectrum

• Pink light emitted from hydrogen when exposed to electric current

• Specific wavelengths and frequency of light

• Electromagnetic radiation - LIGHT

Light

• Electromagnetic radiation

• Gamma, Xrays, UV, Visible, IR, Microwaves and Radio waves

• Visible Light: Violet, Blue, Green, Yellow, Orange and Red

• Wavelength (λ) – distance between 2 wave peaks (m or nm)

• Frequency (ν) – the number of wave peaks per second (Hertz)

• Photon – a particle of electromagnetic radiation having no mass and carrying a quantum of energy

• Quantum – the minumum amount of energy that can be lost or gained by an atom

How atoms give off light…

Using the Bohr Model to predict light

• Example:– What color light is emitted by the hydrogen

atom when an electron transitions from n = 3 to n = 2?

– What wavelength is released when an electron falls from n = 4 to ground state

– What type of electromagnetic radiation is released when an electron falls from n = 4 to n = 3?

Particle Wave-Duality

• Electrons are made of particles (photons)

• They exhibit wave behavior

The Quantum Model

• The electron cloud model• The Heisenberg Uncertaininty principle – it is

impossible to know exact location of electron• Only a probably location is known• Electron do not orbit 2D• Electron are found in a probable 3D region of

space around the nucleus• Probability Model

Bohr vs Electron Cloud