ARRANGEMENT of ELECTRONS in ATOMS

CHAPTER 4

DESCRIBING THE ELECTRON

Questions to be answered:

• How does it move?

• How much energy does it have?

• Where could it possibly be located?

WAVE – PARTICLE NATURE of LIGHT

Electrons can move as particles

or as waves.

WAVE NATURE

• Proposed by Louis de Broglie (1924)

• Electrons could be considered waves confined to the space around the nucleus.

• Only certain wavelengths and frequencies could exist.

The wave can be described by•Wavelength ()

•Frequency ()

•Energy (E)

WAVELENGTH

(lambda)

• The distance between the crests of a wave

• Units: meters or nanometers• 109 nm = 1 m

FREQUENCY • The number of waves that

pass/ second• Units:

•1/sec = 1 hertz (1 hz)

SPEED of LIGHT (add notes in margin)

• A constant.

• Symbol: c

• c = 3.00 x 108 meters/ second

• Fastest possible speed.

c= and are inversely proportional.• Long wavelength = low frequency.

• Short wavelength = high frequency.

• All wavelengths must be in m.

SAMPLE PROBLEMS• What is the wavelength of light

if it’s frequency is 1015 Hz?

• What is the frequency of light if its wavelength is 500 nm? Hint: convert to meters first!

ELECTROMAGNETIC SPECTRUM

VISIBLE REGION ROY G BIV

350 nm = violetto

750 nm = red

THE ELECTROMAGNETIC SPECTRUM

Region Wavelength

Gamma .01 – 0.10 nm

X rays .10-10 nm

UV 10-100 nm

Visible 350 – 750 nm

IR 1000nm - .01cm

Radio waves 1–1000 meters

PARTICLE NATURE of LIGHT

• Some properties of light cannot be explained by wave theory:WHITE HOT OBJECTS

andPHOTOELECTRIC EFFECT

“WHITE HOT” OBJECTS• When objects are heated they give off

light.• Wave theory predicts that only UV light

would be emitted but

RedYellow

White light are emitted

PHOTOELECTRIC EFFECT• Emission of electrons by certain

metals when light shines on them.

• The light must be of a certain frequency to “knock” an electron from the metal surface . (Einstein, 1905)

QUANTUM ENERGY

• White hot objects and the photoelectric effect both emit small, specific amounts of energy called

QUANTUM • A finite quantity of energy that can

be gained or lost by an atom• Proposed by Max Planck

ENERGY of a QUANTUM

• An individual QUANTUM is known as a PHOTON of light and has energy:

E = h• h = Planck’s constant • h = 6.626 x 10-34 Joules · sec

CALCULATIONS of PHOTON ENERGY

• Given light with frequency 450 hz, what is the energy of the photon?

• What is the energy associated with light with a wavelength of 750 nm?

Homework: spectroscopy calculations worksheet