I. Waves & Particles

Ch. 5 - Electrons in Atoms

Properties of Waves

Many of the properties of light may be described in terms of waves even though light also has particle-like characteristics.

Waves are repetitive in nature

A. Waves

Wavelength () - length of one complete wave

Frequency () - # of waves that pass a point during a certain time period hertz (Hz) = 1/s

Amplitude (A) - distance from the origin to the trough or crest

A. Waves

Agreater

amplitude

(intensity)

greater frequency

(color)

crest

origin

trough

A

Electromagnetic Radiation

Electromagnetic radiation: (def) form of energy that exhibits wavelike behavior as it travels through space

Types of electromagnetic radiation: visible light, x-rays, ultraviolet (UV),

infrared (IR), radiowaves, microwaves, gamma rays

Electromagnetic Spectrum

All forms of electromagnetic radiation move at a speed of about 3.0 x 108 m/s through a vacuum (speed of light)

Electromagnetic spectrum: made of all the forms of electromagnetic radiation

B. EM Spectrum

LOW

ENERGY

HIGH

ENERGY

B. EM Spectrum

LOW

ENERGY

HIGH

ENERGY

R O Y G. B I V

red orange yellow green blue indigo violet

Ionizing radiation

Glossary Entry

• Subatomic particles or electromagnetic waves energetic enough to detach electrons from atoms or molecules, ionizing the atoms or molecules.

Gamma rays, X-rays, high energy ultraviolet light, alpha particles, and beta particles are examples of ionizing radiation.

B. EM Spectrum

Frequency & wavelength are inversely proportional

c = c: speed of light (3.00 108 m/s): wavelength (m, nm, etc.): frequency (Hz)

B. EM Spectrum

GIVEN:

= ?

= 434 nm = 4.34 10-7 m

c = 3.00 108 m/s

WORK: = c

= 3.00 108 m/s 4.34 10-7 m

= 6.91 1014 Hz

EX: Find the frequency of a photon with a wavelength of 434 nm.

C. Quantum Theory

Photoelectric effect: emission of electrons from a metal when light shines on the metal

Hmm… (For a given metal, no electrons were emitted if the light’s frequency was below a certain minimum – why did light have to be of a minimum frequency?)

C. Quantum Theory

Planck (1900)

Observed - emission of light from hot objects

Concluded - energy is emitted in small, specific amounts (quanta)

Quantum - minimum amount of energy change

C. Quantum Theory

Planck (1900)

vs.

Classical Theory Quantum Theory

C. Quantum Theory

Einstein (1905)

Observed - photoelectric effect

C. Quantum Theory

E: energy (J, joules)h: Planck’s constant (6.6262 10-34 J·s): frequency (Hz)

E = h

The energy of a photon is proportional to its frequency.

C. Quantum Theory

GIVEN:

E = ? = 4.57 1014 Hzh = 6.6262 10-34 J·s

WORK:

E = h

E = (6.6262 10-34 J·s)(4.57 1014 Hz)

E = 3.03 10-19 J

EX: Find the energy of a red photon with a frequency of 4.57 1014 Hz.

C. Quantum Theory

Einstein (1905)

Concluded - light has properties of both waves and particles

“wave-particle duality”

Photon - particle of light that carries a quantum of energy