Chapter 7

Electronic Structure of Atoms

The Wave Nature of Light

• The electronic structure of an atom refers to the arrangement of the electrons.

• Visible light is a form of Electromagnetic radiation (EMR).

• Radiation carries energy through space• EMR is characterized by its wave

Wave Properties

• All waves have a characteristic wavelength, λ (lambda), and amplitude, A.

• The frequency, ν (nu), of a wave is the number of cycles which pass a point in one second.

• The units of ν are Hertz. (1Hz = 1/s)

• The speed of EMR is always the same no matter what the wavelength or frequency.

• EMR speed is the speed of light.

• c is the symbol for the speed of light

• C = 3.0 x 108m/s

• The relationship between frequency (ν ) and wavelength

(λ )is shown by the equation

c = λ νWhere

c = the speed of light = 3.0 x 108m/s

λ = the wavelength of the wave

ν = the frequency of the wave (Hz)

• Frequency and wavelength are inversely related.

• Since the speed of the wave is constant (3.0 x 108m/s) , if the frequency is known, the wavelength can be determined.

• Likewise, if the wavelength is known, the frequency can be determined.

Light as Electricity and Magnetism

o Max Planck determined mathematically that light is both magnetism and electricity.

o He determined the Energy in a photon is directly related to its frequency .

oIf the frequency is multiplied by Planck’s constant (6.6261 x 10-34 J-s), the Energy of the photon can be determined.

o This relationship is represented in the formula

E=h νWhere E = Energy h = 6.6261 x 10-34 J.s (Planck’s

constant) ν = frequency

How does this relate to atomic models?

Thomson’s Model

Thomson had the Plum Pudding Model.Negative particles interspersed in positive atom, NEUTRALLY CHARGED.

Changed Dalton’s Model:Atom is NOT smallest particle of matter.

•Rutherford’s Model

PROBLEMS•Could not explain the chemical properties of the elements.•Why do metals give off characteristic colors when heated in a flame?•When heated iron glows red, then yellow, then white. WHY?

Dense positive center with electrons outside the nucleus.

BOHR MODELGOAL: To improve Rutherford’s Atomic Model

QUANTUM MECHANICAL MODEL OF THE ATOM

• The quantum mechanical model is a way of describing the atom through electron movement.

• Electrons are arranged in orbitals (path the electron follows) in Energy levels (distance from the nucleus) around the nucleus.

• If the electrons gain a photon (specific amount) of energy they can travel to higher energy levels.

• The energy level the electron

travels to will be determined by the amount of energy in the photon.

• The electron cannot maintain this higher energy level and eventually returns to a lower level.

• The energy is released as it travels down in the form of EMR.

• The color you see depends on the wavelength of the light released.

Determining the Energy of the photon.

• To determine the Energy of the photon released, we use the formula

E=h ν

Example:

• PROBLEM:What is the energy of a photon with a frequency of 3.7 x 107Hz?

• SOLUTION:Use the formula E=h ν.E = ? h= 6.6261 x 10-34 J-s ν = 3.7 x 107Hz

E= (6.6261 x 10-34 J-s ) (3.7 x 1071/s)= 24.51657 x 1027 JThen 24.51657 is not a number between 1 and 10.2.451657 x 10 28 J