light is an electromagnetic wave em wave- a form of energy that exhibits wavelike behavior as it...
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Light is an electromagnetic wave
• EM wave- a form of energy that exhibits wavelike behavior as it travels through space
• All the forms of EM radiation form the electromagnetic spectrum
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Properties of EM waves
• Speed- all forms of EM radiation travel at 3 x 108 m/s in a vacuum
• Wavelength-the distance between 2 consecutive waves
• Frequency- the # of waves that pass a stationary pt. in one second
• Amplitude- the height of a wave measured from the origin to its crest
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Photoelectric Effect
• Refers to the emission of electrons from a metal when light of a specific frequency (or energy) shines on the metal
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Particle Description of Light
• Quantum- the minimum quantity of energy that can be lost or gained by an atom
• This relationship is expressed as:
E = hv
Where E = energy
h= Planck’s
constant
v= frequency of light
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The Dual Nature of Light
• Light exhibits many wavelike properties but can also be thought of as a stream of particles called photons.
• Photon- a particle of EM radiation having zero mass and carrying a quantum of energy
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Bohr’s Model• The electron can circle the nucleus only in
allowed paths or orbits
• In an orbit, an electron has a fixed energy
• The lowest energy state is closest to the nucleus
• An electron can move to a higher orbital if it gains the amount of energy equal to the difference in energy between the initial orbit and the higher energy orbit
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Line Emission Spectra• The lowest energy state
of an electron is the ground state.
• A state in which that atom has a higher energy potential is called an excited state.
• As the excited electron falls back to its ground state, it releases EM radiation of an energy that corresponds to the amount of energy gained to reach the excited state.
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energy of emitted photon = (atom energy before) - (atom energy
after)
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• When the EM radiation released is passed through a prism or diffraction grating- it is separated into a series of specific frequencies of visible light.
• This is referred to as a line emission spectra
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DeBroglie’s Idea
• Suggested that electrons could also have a wave nature much like light.
This was based on the fact that:
Electrons can be diffracted (bending)
Electrons exhibit interference (overlapping that results in a reduction of energy)
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• It is impossible to determine simultaneously both the position and velocity of an electron.
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Schrodinger’s Wave Equation
• Laid the foundation for modern quantum theory.
• Quantum Theory describes mathematically the wave properties of electrons.
• The solutions to this equation give only the probability of finding an electron at a given location.
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• Electrons do not travel in neat orbits
• They exist in three-dimensional regions called orbits that indicate the probable location of an electron.
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The location of electrons within the atom can be described using quantum numbers:
Principle Orbital (Angular Momentum)MagneticSpin
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Principle Quantum Number
• Gives the principle energy level
n= 1, 2, 3, etc.
• Maximum # of Electrons for Orbitals:
1st- 2
2nd – 8
3rd – 18
4th - 32
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Orbital Quantum Number
• Tells the shape or type of orbital
• s orbital is doughnut shaped
• p orbital is dumbbell shaped
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Suborbital # of electrons # of orbitals
s 2 1
p 6 3
d 10 5
f 14 7
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Magnetic Quantum Number
• Designates specific regions of space w/in each energy sublevel
(s, p, d, f)
• Ex.
p sublevel has 3 orbitals
(px, py, pz)
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Spin Quantum Number
• Designates direction of electron spin
• Electrons w/in an orbital spin in opposite directions
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Governing Rules and Principles
• Pauli Exclusion Principle- only 2 electrons in each orbital
• Aufbau Principle- electrons must occupy lower energy orbitals first
• Hunds Rule- a second electron can not be added to an orbital until each orbital in a sublevel contains an electron
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Summary:
Principle Energy Level
Orbitals Max. Electrons
1 s 2
2 s p 8
3 s p d 18
4 s p d f 32