4.1 Refinements of the Atomic Model

Mr. Chris Walters Williamstown Schools

The Dual Nature of Light

• Experimentation has shown that light behaves as both a wave (energy) and as a particle (matter).

• This concept seems to defy logic but is supported.

• • “A form of energy that displays wavelike behavior as it travels through space” Travels at 3.0 x 10 vacuum (c) 8 m/sec in a

Has the measurable properties of wavelength(



) and frequency (



) The speed of light is equal to the product of wavelength times frequency

.

c = λ • ν

All the wavelengths of light form a CONTINUOUS SPECTRUM FREQUENCY is measured in HERTZ (Hz). A Hz is one wave occurring per second.

Visible Light

• • that portion of the electromagnetic spectrum from wavelengths 375 nm to 725 nm Illustrated in 7 colors ROY G BIV (from longest wavelength to shortest)

Light as Particles

• The wave theory of light encountered two problems – It predicted that heated objects would give off ultraviolet light, they emit visible light – It could not explain the Photoelectric effect

Photoelectric Effect

• The Photoelectric effect is the emission of electrons by metals when light shines on them – Only certain frequencies of light caused the effect

Explanation - Planck

• • • Max Planck (1858-1947) proposed that energy was given off in specific quantities or

Quanta.

(singular: Quantum) Planck proposed the following equation E= h  , where h was a constant value.

Planck’s constant (h) = 6.626 x 10 -34

Continuation - Einstein

• • An individual particle of light is called a photon.

Einstein proposed that absorption of photons at certain quanta explained the photoelectric effect.

Exciting Electrons to release light

• When atoms in the gaseous state are heated they increase in PE then return to original state as they emit light.

– As they are heated the electrons leave the

ground state

and become

excited.

– They give off light in specific amounts ( quanta ).

– This can be illustrated in the line spectrum

Bohr Model of the Atom

• • • Niels Bohr (1885-1962) proposed a model using this new information.

It showed the orbits of the electrons a specific quantized distances from the nucleus.

Bohr’s model worked well on Hydrogen, but failed to match data with more complicated atoms and their line spectra.

Spectroscopy

• • A spectroscope is an instrument that separates light into a spectrum that can be analyzed . This allows the light to be examined and its atomic source discovered.

Quantum Model

• • • Replaced the orbits of Bohr with regions of space in which the electrons are located called orbitals.

Orbitals are quantized.

Quantum theory mathematically explains the wave properties of electrons and other small particles.

• Louis deBroglie (1892 1987) proposed the dual nature of electrons.

Louis deBroglie

Schrodinger’s Wave Equation

• Erwin Schrödinger proposed his wave equation that mathematically explains electron action.

Heisenberg’s Uncertainty Principle

• Werner Heisenberg contributed his Uncertainty Principle which states it is not possible to know both the velocity and position of a particle at the same time.