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CHAPTER 13: Electrons in the Atom

2Quantum Mechanical Model of

the Atom and Ernest Schrodinger

The model of the atom was

developed based on the

study of light.

3Electromagnetic radiation.

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Properties of Light

• Electromagnetic radiation-is a form of energy that exhibits wavelike behavior as it travel through space.

• Examples x-rays, UV, infrared light, microwaves, radio waves

• Electromagnetic spectrum- all electromagnetic radiation, arranged according to increasing wavelength.

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The Spectrum

VIBGYORVIBGYOR

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Facts about Electromagnetic Radiation

• The size of a radio wavelength (crest to crest) is approximately the length of a football field. The size of a gamma ray wavelength is approximately the size of a nucleus of an atom.

• X-rays have enough energy to damage human cells which is why lead vests are worn.

• The visible part of the spectrum is the only part that can be seen with the human eye. However, other animals can see parts of the spectrum that humans can’t. For example, a large number of insects can see ultraviolet (UV) light.

• Gamma rays are given off by stars, and by some radioactive substances. Lead or concrete is needed in order to block them out.

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Speed of Light

• C= speed of light. This is a constant. It is always

3.0 x 108 m/s

c •λλ = Wavelength. Units = Wavelength. Units of meters. It is the of meters. It is the distance between two distance between two corresponding points corresponding points on a wave. on a wave. •ν = frequency. Units ν = frequency. Units of hertz (Hz) or 1/sec. It of hertz (Hz) or 1/sec. It is the number of waves is the number of waves that pass a given point that pass a given point in 1 sec. in 1 sec.

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Wavelength

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Wavelength and Frequency are inversely related

• As one increases, the other decreases and vice versa.

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Example:

• The wavelength of a red light is 5.00 x 10-6

meters. What is the frequency?

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Photoelectric Effect

• Is the emission of electrons by certain metals when light shines on them

12E

nerg

y E

nerg

y

Excited Atom Excited Atom

Lower Energy Lower Energy State Atom State Atom

Photon of Red Photon of Red Light is Emitted Light is Emitted

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Light is Emitted. WHY?

• As energy is applied, the atom leaves a lower energy state (called the ground state) and reaches a higher energy state (called the excited state).

• As the atom looses energy, it will return to the ground state. As it returns to the ground state, a photon of light is emitted and observed.

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Energy

• E= energy. Units of J

• h= Planck’s constant (6.626x10-34 J.S). This number does not change.

• v= frequency. Units of Hz or 1/sec.

h E

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Energy and Frequency are directly related

• As one increases, so does the other. As one decreases, so does the other.

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Example:

• A photon of light has a frequency of 1.1 x 1010 Hz. What is the energy of this photon?

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Review:

• Which type of energy on the spectrum has the greatest energy?

• Which type of energy on the spectrum has the largest wavelength?

• Which type of VISIBLE energy (ROYGBIV) has the largest wavelength?

• Which type of energy on the spectrum has the smallest frequency?