Structure-Oriented Approach in Chemical Education - Essentials of Chemical Education - page 313

4th main group 5th main group 6th main group 7th main group

H

H

C

H H

H

N O

F

C

Ball-and-stick model Structural symbol

P S

Cl

Si

H

CH 4

HC H

Br

H

Stoichiometric
symbol

Structural symbol
(simplyfied)

i

tetravalent divalent monovalent

trivalent

Fig. 10.23 Bonding valences of nonmetal atoms in molecules

rotating mirror allows the sample beam and
the reference beam to pass alternately

Sample Sample
beam

IR -Light -
source

Tausendstel mm

Detector Monochro-

mator
(decomposition
by wave length)

3.5 5

3 4 4.5

100

80

50
40

Reference
beam V

Paper

20

0%

writer

3500 3000 2500 2000

amplifier

cm ~ 1

Motor

Infrared spectrum of hydrogen chloride
in carbon tetrachloride solution

Beam path in the IR-spectrometer

Fig. 10.24 Set-up for infrared spectroscopy, with a solution of HCl in CCl 4 as an example

methods. They make use of the energetic interaction that exists between electro-
magnetic radiation and the molecules of a specific substance. Infrared spectroscopy,
for example, works with long-wavelength infrared radiation (see Fig. 10.24 ): this
beam of radiation excites the molecules in a solution to vibrate in different ways:
stretching vibration causes a change of bond length, bending vibration causes a
change of bond angles. Specific frequencies are being absorbed.