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Lecture 3

CHEM 1A03 Lecture Notes - Lecture 3: Threshold Energy, Rydberg Constant, Balmer Series

Course Code
David Brock

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Unit 3 – Atomic Structure and Theory Sept 14, 2014
Electro Magnetic Spectrum
-All light is made up of electromagnetic waves
-Composed of an electrical component and a perpendicular magnetic component
travelling in the same direction
-Wavelength ( λ ) = distance
between peaks or troughs
-Frequency ( v ) =
wavelengths / time
-Speed of light ( C ) = 2.9979
x 108
C = v λ
-Red, orange, yellow, green,
blue, indigo, violet
1. Energy Frequency
2. Energy 1/ λ
Atomic Spectra
-Each element has a unique line spectrum

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Unit 3 – Atomic Structure and Theory Sept 14, 2014
Atomic Properties
Niels Bohr
-Mostly empty space
-Contains a nucleus, composed of neutrons and protons
-Nucleus is relatively small but contains almost the entire mass
-Electrons surround the nucleus, acting as particles and waves
Max Planck
-Energy is discontinuous and comes in quanta
-Each quantum of energy is a photon
-Energy of a photon = frequency x Planck’s constant
-E = h v ; h = 6.626 x 10-34J/s
Photoelectric Effect
-No circuit, plates separated by a vacuum
-Only way to complete the circuit is to
cause an electron to jump from one plate to
-If energy was not quantized, shining any
photon of light with any amount of energy
for an extended period of time will
eventually provide enough total energy for
an electron to be ejected
-Small frequency – long amounts of time or
more intense (brighter) light caused no
-Larger frequency – Certain point, ammeter
gave a reading
-Ephoton > Threshold Energy (work function hvo) of metal, electrons are ejected with
kinetic energy
-Even larger frequency – No chance in ammeter
-Higher energy light is not equal to more electrons being ejected, but electrons with
higher kinetic energy
-One photon for one electron
-After threshold energy, double intensity and ammeter will double
-E incident light = Threshold Energy + Kinetic Energy of electron
Albert Einstein
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