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 at n = 2
Quantum
of energy
E at n = 1
absorption
relaxation
Emission
Of photon
E2- E1 = hv
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