ELECTROMAGNETIC RADIATION AND THE NEW ATOMIC MODEL

PROPERTIES OF LIGHT  Electromagnetic Radiation  A form of energy  Is like a wave when it travels through space  What are some examples of radiation?

PROPERTIES OF LIGHT  Electromagnetic Spectrum?  All forms of Electromagnetic Radiation are arranged in a spectrum according to their ENERGY!

PROPERTIES OF LIGHT  Waves are a repeating pattern of motion  Wavelength (λ) The length of one repeat of the pattern!  Meters, nanometers  Frequency ( ν ) the amount of wavelengths that occur in a unit of time (usually seconds)  Waves/sec = Hertz (Hz)

PROPERTIES OF LIGHT  For electromagnetic radiation…  Wavelength and the frequency are related to a wave’s speed c = λν  c is in meters per seconds (m/s)

PHOTOELECTRIC EFFECT  Scientists shined a light on a metal…  Some lights caused the metal to eject an electron!  Some lights didn’t…  They tried increasing the intensity of the lights that didn’t work and that didn’t help either!

PHOTOELECTRIC EFFECT  Planck realized that while all objects emit electromagnetic radiation (EMR), they don’t emit it continuously like a gradient  Instead they emit EMR in little packets called QUANTA.

QUANTA  A QUANTUM of energy is a specific amount of energy gained or lost by an atom  What does this mean?

QUANTA  Planck’s relationship proposal between quantum energy and electromagnetic wave frequency E = h ν  E = energy in joules (J)  h = Planck’s constant (Js) = x Js

QUANTA  Einstein proposed:  Electromagnetic radiation is both  wave-like  particle-like  Photon – the particle form of a wave of electromagnetic radiation (particle of energy)  E photon =hv

EXCITED STATES AND EMISSION SPECTRA  Ground state – relaxed/stable state of matter; lowest energy state  When a certain quantum of energy hits an atom an electron can become excited or raised out of the ground state!

EXCITED STATES AND EMISSION SPECTRA  Emission – when an excited electron relaxes to the ground state, a photon is released.  Absorption – when a ground state electron receives the right quanta of energy to become excited.

EXCITED STATES AND EMISSION SPECTRA  A continuous spectrum from hydrogen – what would happen if hydrogen could be excited by any amount of energy.  Line-emission spectrum – the distinct bands of light observed from excited gases

EXCITED STATES AND EMISSION SPECTRA absorption relaxation Emission Of photon E 2 - E 1 = hv Quantum of energy E at n = 2 E at n = 1

BOHR’S HYDROGEN ATOM MODEL  Bohr thought electrons could only circle the atom in specific pathways, or orbitals.  The orbitals were specific energy levels and distances away from the nucleus

BOHR’S HYDROGEN ATOM MODEL