Electrons

Light Properties of Waves Particles

Waves

Electromagnetic radiation Energy Travels like waves All kinds speed of 3.00 x 108 m/s in a vacuum Move repetitively Measured properties Wavelength Frequency

Electromagnetic Spectrum

Wavelength Distance between two corresponding points on adjacent waves Units = distance Symbol = λ

Frequency Number of waves that pass a point in a specific time normally 1 sec Units = waves / second or Hz Symbol = ν

Wavelength vs Frequency The 2 properties are inversely related – as one goes up the other goes down c = λν c= speed of light (m/s) λ = wavelength (m) ν = frequency (1/s or Hz) If you know one variable you can find the other What is the frequency of a wave whose wavelength is 0.01m?

Particle Theory

Photoelectric Effect Emission of electrons when light strikes metal Only happens when frequency of light is above a minimum amount for each metal Intensity does not matter

Planck Objects release electromagnetic radiation in packets 1 packet = Quantum = smallest amount of energy gained or lost by an atom The energy is related to the frequency of the wave E = hν E = energy in J H = Plank’s constant (6.626 x 10-34 J∙s) ν= frequency

Planck Problem E = hν h = 6.626 x 10-34 J∙s (Plank’s constant) Determine energy in joules of a photon w/ frequency of 1.29x1017Hz.

Einstein ER has wave and particle properties Each particle has a quantum of energy Photon – particle of ER with no mass and a quantum of energy Matter absorbs energy ONLY in whole numbers of photons To eject an electron from metal, the photons must have a minimum energy or a minimum frequency Ephoton = hν

Line-Emission Spectrum Ground state- lowest energy state of atom Excited state- higher in potential energy than ground state When electricity is run through a gas Atoms get excited Drop back to ground state Light energy is released If we look at that light through a prism it breaks down into the component colors of light called line-emission spectrum Every element has own unique spectrum

H’s line-emission spectrum showed differences between energy states bare fixed Electrons can only exist in certain energy states Which leads to Bohr Model of atom

Bohr Model Electrons exist in certain energy levels around the nucleus Closer to nucleus is lower energy Further out higher energy Cannot exist between energy levels

De Broglie Electrons act like both waves and particles Act as confined waves, can only exist at certain frequencies Can be interfered with