# CHEM 1320 Study Guide - Hmu Language, Diamagnetism, Fluorine

15 pages42 viewsFall 2013

Chapter 7: Quantum Theory and the Electronic Structure of

Atoms

10/11

Wavelength ( ): peak-to-peak distance on successive wavesλ

Amplitude: vertical distance from midline to peak

Frequency ( ): # of waves pass through a point in 1 sec. ν

(Hz=1cycle/s)

Speed ( ) of the wave: X υ λ ν

Higher the frequency, shorter the wavelength

Lower the frequency, longer the wavelength

Inverse relationship

Maxwell (1873): visible light is electromagnetic (EM) waves.

EM radiation: emission & transmission of energy in the form of

electromagnetic waves.

Speed of light (c)= 3.00 X 10^8m/s

ALL EM radiation: λX ν=c

Violent=shortest wavelength, longest frequency

Red=longest wavelength, shortest frequency

Frequency:

Units of frequency:

Sec^-1 S^-1 Cycles per second (cps) Hz (Hertz)

Symbol: (ν) (Greek nu)

Wavelength:

Unit: (λ)

Different λ=different kind of light

Measured in nm (one billionth of a meter)

250nm=250 X 10^-9m

Frequency Wavelength

Can convert λ and frequency (ν):

In meters λ=c/ν c=3.00 X 10^8m/s

A radio station is 103.5 FM. What wavelength does it broadcast?

103.5FM=103.5MHz=103.5 million s^-1

λ=3.00 X 10^8 m/s

---------------------- = 2.8 m (~10ft)

103,500,000s^-1

What is the frequency of light if its wavelength is 200 m?

=νc/λ

=3.00 X 10^8 m/s

---------------------- = 1,500,000s^-1 1.5 X 10^6s^-1

200m

Visible=most intense

Wavelength=most abundant

UV=most damaging

Mystery #1

“Heated Solids Problem”

-Heated solids emit EM radiation over a wide range of

wavelengths.

White-hot object: hotter than red-hot

Different wavelengths different amounts of energy

Energy (light) is emitted or absorbed in discrete units (quantum).

E=h X ν

Planck’s constant (h)

h=6.63 X 10^-34 Js

What is the energy of UV light with a frequency of

1.00 X 10^15 s^-1?

E=hν=(6.63 X 10^-34 Js)(1 X 10^15 s^-1)

E=6.63 X 10^-18 J

E=hν=hc/λ Since ν=c/λ

Compare to a radio wave of λ 3 X 10^9 m

E= hc/λ =(6.63 X 10^-34 Js)(3.00 X 10^8 m/s)

-------------------------------------------------

3 X 10^9 m

E=6.63 X 10^-35J

What happens when light hits matter?

IR-molecules vibrate, matter heats up

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