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 = hν E = energy in joules (J) h = Planck’s constant (J•s)
= 6.626 x 10-34 J•s
QUANTA Einstein proposed:
Electromagnetic radiation is both wave-like particle-like
Photon – the particle form of a wave of electromagnetic radiation (particle of energy)
Ephoton=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
e
e
absorption
e
e
relaxation
EmissionOf
photonE2- E1 =
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