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

BOHR’S HYDROGEN ATOM MODEL