The ELECTRON: Wave – Particle Duality

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The Dilemma of the Atom

• Electrons outside the nucleus are attracted to the protons in the nucleus

• Charged particles moving in curved paths lose energy

• What keeps the atom from collapsing?

Wave-Particle DualityJJ Thomson won the Nobel prize for describing the electron as a particle.His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The

electron is a

particle!

The electron is an energy

wave!

The Wave-like Electron

Louis deBroglie

The electron propagates through space as an

energy wave. To understand the atom, one must understand

the behavior of electromagnetic waves.

c = c = speed of light, a constant (3.00 x 108 m/s) = frequency, in units of hertz (hz, sec-1) = wavelength, in meters

Electromagnetic radiation propagates through space as a wave moving at the speed of light.

E = h

E = Energy, in units of Joules (kg·m2/s2)h = Planck’s constant (6.626 x 10-34 J·s) = frequency, in units of hertz (hz, sec-1)

The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation.

Long Wavelength

=Low Frequency

=Low ENERGY

Short Wavelength

=High

Frequency=

High ENERGY

Wavelength Table

Answering the Dilemma of the Atom

• Treat electrons as waves• As the electron moves toward the

nucleus, the wavelength shortens• Shorter wavelength = higher

energy• Higher energy = greater distance

from the nucleus

The Electromagnetic Spectrum

This produces bandsof light with definite wavelengths.

Electron transitionsinvolve jumps of

definite amounts ofenergy.

…produces a “bright line” spectrum

Spectroscopic analysis of the hydrogen spectrum…

Flame Tests

strontium sodium lithium potassium copper

Many elements give off characteristic light which can be used to help identify them.

Exclusion NoticeThe contents of the next two slides reference equations that are no longer included on the AP Chemistry equations sheet, and can no longer be tested in a quantitative sense

Electron Energy in Hydrogen

218

22.178 10electronZE x Jn

***Equation works only for atoms or ions with 1 electron (H, He+, Li2+, etc).

Z = nuclear charge (atomic number)n = energy level

Calculating Energy Change, E, for

Electron Transitions2 2

182 22.178 10final initial

Z ZE x Jn n

Energy must be absorbed from a photon (+E) to move an electron away from the nucleusEnergy (a photon) must be given off (-E) when an electron moves toward the nucleus