Week 1 Review (Chem)

Radio waves

farthest left of scale- longest wavelength

• wavelength = one millimeter to 100 kilometers (10^5 to 10^-1)

• excites spin of nucleus- used in MRI

Microwaves

after radio waves on spectrum

• wavelength = 100 um to 100 cm

• excites spin of electrons and rotation of H20 and fats around 12 cm

Infrared

after microwaves on spectrum

• wavelength= 800 to 1,000 nm

• causes vibration in molecules

• used in night vision goggles

• excites OH in ethanol (measure toxicity)

Visible light

after infrared waves on spectrum

• colors detected by human eyes (rainbow)

• 300 to 800 nanometers

• excites valence electrons to higher energy level

Red wavelength (visible light)

approx. 620-750 nm

Orange wavelength (visible light)

approx. 590-625 nm

Yellow wavelength (visible light)

570 to 590 nm

Green wavelength (visible light)

approx. 495 to 570 nm

Blue wavelength (visible light)

approx. 380 to 500 nm

Violet wavelength (visible light)

approx. 380 to 450 nm

Ultraviolet

after infrared on the spectrum

• 10 nm to 300 nm

• excites valence electrons

• Lyman series for H emission

• Causes sun burns

X-ray

after ultraviolet on spectrum

• approx. 0.01 to 10 nm

• excites core electrons

• used in medicine for invasive imaging

• causes cell mutations

Gamma Ray

after x-ray on spectrum- shortest wavelength

• less than 100 picometers (1×10⁻¹¹ meters)

• associated with decay of atom nucleus

• emitted from stars

Electromagnetic Radiation Trends

• Energy and frequency increases from left to right

• Wavelength decreases from left to right

Spectroscopy

light and matter are intimately linked

Electromagnetic Radiation

a wave composed of electric and magnetic fields that oscillate perpendicularly

Speed of Light

(Universal speed limit)

• 3 × 10^8

Wavelength

lambda (meters or nanometers)

• calculated by finding height and trough

• directly proportional to frequency

Frequency

“nu”- number of cycles per unit time

• s^-1 or Hz)

• directly proportional to wavelength

• high= lots of waves; low= less waves

Amplitude

height of wave

Frequency equation

v (frequency)= c (speed of light)/ lambda (wavelength)

Wavelength equation

lambda (wavelength)= c (speed of light)/ v (frequency)

1 nm

10^-7 m

Light has energy

• E= hv

• E= hc/lambda

h

• Planck’s constant

• 6.626 × 10^-34 JS ~ 7×10^-34 JS

The photoelectric effect

• emitted electrons have a certain kinetic energy (KE)

• Photon

• light is a wave and a particle

Photon

pocket of light

The photoelectric effect equation

Ephoton= Ethreshold + KE

• Ephoton (hv)

• Ethreshold (work function)

E

energy of incoming photon

Ethreshold

minimum energy required to eject an electron from the metal surface… aka the work function

KE

kinetic energy of an ejected electron

Energy and frequency

directly related

Energy and wavelength

inversely related

Frequency and wavelength

inversely related

Photon has to have ____ energy to overcome metal’s work function and be ejected

enough

Excess energy of photon

becomes KE of ejected electron