Quantum Theory, Part I

The Atom

Day 4

Prism White light is made up of all

the colors of the visible spectrum.– Passing it through a prism

separates it.

Spectrum - The range of frequencies present in light.– White light has a

continuous spectrum.» All colors are possible.» i.e. A rainbow

Continuous Spectrum

Joseph von Fraunhofer

Invented the spectroscope. Discovered absorption spectra when

studying sunlight. – Discovered 574 dark lines appearing

in the solar spectrum. » Called Fraunhofer lines in his

honor. Invented the diffraction grating and in

doing so transformed spectroscopy from a qualitative art to a quantitative science by demonstrating how one could measure the wavelength of light accurately.

Gustav Kirchhoff & Robert Bunsen • Studied emission spectra of heated elements• Referred to as spectrum analysis.

• For this work, Bunsen and his laboratory assistant, Peter Desaga, perfected a special gas burner • The clean, hot, non-luminous flame did not interfere

with the colored flame given off by the test material.• Called simply the "Bunsen burner"

• Kirchhoff suggested that similarly colored flames could be differentiated by looking at their emission spectra through a prism.

• When he shone bright light through such flames, the dark lines in the absorption spectrum of the light corresponded in wavelengths, with the wavelengths of the bright, sharp lines characteristic of the emission spectra of the same test materials.

Formalized 3 laws that describe the spectral composition of light.

1. A hot solid object produces light with a continuous spectrum.

2. A hot tenuous gas produces light with spectral lines at discrete wavelengths (i.e. specific colors) which depend on the energy levels of the atoms in the gas.

3. A hot solid object surrounded by a cool tenuous gas (i.e. cooler than the hot object) produces light with an almost continuous spectrum which has gaps at discrete wavelengths depending on the energy levels of the atoms in the gas.

Kirchhoff ’s Laws

Sodium

Line Emission Spectra

Bright lines represent ’s being released by the electrons.

Black spaces represent ’s NOT absorbed/released by the electrons.

Hydrogen

Line Spectra of Some Elements

IMPORTANT NOTE: Each element produces a slightly different line emission spectra.

(Element Fingerprint)

Each element’s atoms contain electrons that absorb and release a __________ combination of of light.

Emission and absorption spectrums are ______________

True continuous spectrums are very rare and essentially only occur _____________.

opposites

in a vacuum

Things to Note!

unique

Explanation of Emission Spectra Let’s look at Hydrogen!

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

Explanation of H’s Emission Spectra

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

E = -21.78 x 10-19 J

Unstable (excited state) E = -5.45 x 10-19 J

E = -2.42 x 10-19 J

E = -1.36 x 10-19 J

E = +16.33 x 10-19 J

E = +15.81 x 10-19 J

E = -0.872 x 10-19 J

E = -0.606 x 10-19 J

E = -0.445 x 10-19 J

1 photon with 16.33x 10-19 J -5.45 x 10-19

- -21.78 x 10-19

1.633 x 10-18

Explanation of Emission Spectra

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

E = 19.36 J

E = 3.03 J

E = 19.36 J

E = -0.445 JE = -0.606 J

E = -0.872 J

E = -1.36 J

E = -2.42 J

E = -5.45 J

E = -21.78 J

E = 16.33 J

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

There are actually _______ possible photons that can be given off by any atom.

21

Why do we only see 4 ’s (4 lines) when there are actually 21 different photons (’s)

being given off?

410 nm 434 nm 486 nm 656 nm

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

• Only 4 of the photons released correspond to visible light.

The rest correspond to in the ______ & ______ regions.

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

IR = less energy (705 nm – 1 x 106 nm)

UV = more energy (20 nm - 395 nm)

UV IR

Why do we only see RED (Pink) with the naked eye?

There are more red photons being given off than any other visible color.

More photons = Higher Intensity = This is the color we see.

n = 1

n = 3

n = 4

n = 2

n = 7n = 6

n = 5

E = -5 J

E = -40 J

E = -25 J

E = -7 J

E = - 10 J

E = -15 J

E = -60 J90 J

Why are Gamma, X-rays, & UV so Dangerous

Why are Gamma, X-rays, & UV so Dangerous

IF A PHOTON WITH WAY TOO MUCH ENERGY HITS AN ELECTRON, IT WILL KNOCK IT CLEAR OUT OF THE ATOM. An atom that has LOST 1/more electrons is called an ______ or a __________. They are extremely dangerous because they are unstable and will destroy other cells in an attempt to gain back the correct # of electrons and be stable/neutral again.

For this reason, these types of radiation are often collectively called ionizing radiation.

+ ioncation