Transcript Atomic Spectra - George Mason University

Atomic Spectra
Lab 1
Light
If we pass light through a prism or diffraction grating, we can see the intensity as
a function of wavelength.
Type of Spectrum
Solids, liquids, and dense gases emit light of all wavelengths, without any
gaps – or a continuous spectrum
Thin gases emit light of only a few wavelengths - an emission or bright line
spectrum.
 If there is a source of light behind it, a thin
gas will absorb light of the same
wavelengths it emits
 this is called an absorption or dark line
spectrum.
Different Emission Line Spectra
H
He
C
Balmer lines
• each element generates its own unique
set of wavelengths of emission or
absorption
• Balmer studied the optical spectrum of
hydrogen and found a pattern in the
wavelengths of its emission lines
Periodic Table of Elements
Group**
Period
1
IA
1A
2
3
4
5
6
8A
1.008
2
IIA
2A
3
4
1
1
18
VIIIA
H
Li Be
6.941
9.012
11
12
Na Mg
22.99
24.31
19
20
3
4
IIIB IVB
3B
4B
21
22
K Ca Sc Ti
39.10
40.08
37
38
Rb Sr
44.96
39
Y
5
VB
5B
23
V
6
7
8
9
10
VIB VIIB
------- VIII ------6B
7B
------- 8 ------24
25
26
6
7
8
9
10
B
C
N
O
F
Ne
10.81
12.01
14.01
16.00
19.00
20.18
13
14
15
16
17
18
11
IB
1B
12
IIB
2B
Al
Si
P
S
26.98
28.09
30.97
32.07
35.45
39.95
29
30
31
32
33
34
35
36
Cl Ar
55.85
58.93
58.69
63.55
65.39
69.72
72.59
74.92
78.96
79.90
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
I
Xe
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
95.94
(98)
101.1
55
56
57
72
73
74
75
76
Cs Ba La Hf Ta W Re Os
132.9 137.3 *138.9 178.5 180.9 183.9 186.2 190.2
104
105
106
107
108
102.9
77
Ir
59
60
61
62
63
107.9
112.4
114.8
118.7
121.8
127.6
126.9
131.3
78
79
80
81
82
83
84
85
86
Pt Au Hg Tl Pb Bi Po At Rn
190.2
195.1
197.0
200.5
109
110
111
112
64
204.4
65
66
67
68
207.2
209.0
(210)
116
118
Uuh
Uuo
(296)
(298)
(?)
69
70
71
140.9
144.2
(147)
150.4
152.0
157.3
158.9
162.5
164.9
167.3
168.9
173.0
175.0
90
91
92
93
94
95
96
97
98
99
100
101
102
103
U Np Pu Am Cm Bk Cf
(238)
(237)
(242)
(243)
(247)
(247)
(249)
Es Fm Md No Lr
(254)
(253)
(222)
114
140.1
(231)
(210)
Uuq
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Actinide Series~ Th Pa
83.80
106.4
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Uuu Uub
(277)
(223)
(226) ~(227) (257) (260) (263) (262) (265) (266) (271) (272)
232.0
4.003
5
54.94
92.91
58
He
52.00
91.22
Lanthanide
Series*
2
50.94
88.91
89
28
16
17
VIA VIIA
6A
7A
47.88
87.62
88
27
15
VA
5A
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
85.47
87
7
13
14
IIIA IVA
3A
4A
(256)
(254)
(257)
Balmer series – set of visible lines
in H spectrum
• For H, the wavelengths are - 374.9 377.0
379.7 383.4 388.8 396.9 410.1
433.9 486.0 656.1
• a simple formula reproduces these
wavelengths
• λ (n) = (364.5 nm * ( n2 /n2 – 4))
where n = 3, 4, 5, …..
other scientists found similar patterns in
other portions of the electromagnetic
spectrum
Paschen series
• Paschen, in the infrared, measured lines
with wavelengths
866.2 874.8 886.0 901.2 922.6
954.3 1004.6 1093.5 1281.4 1874.5
which matched the series
• λ (n) = (820.5 nm * ( n2 /n2 – 9))
where n = 4, 5, 6, …..
Lyman series
• Lyman, in the ultraviolet, a series of lines
with wavelengths
91.9 92.1 92.3 92.6 93.0 93.7
94.9 97.2 102.5 121.5 corresponding
to the series
• λ (n) = (91.1 nm * ( n2 /n2 – 1))
where n = 2, 3, 4, …..
• In fact, scientists soon realized that
hydrogen's spectrum could be broken
down into a large number of series, each
of which had wavelengths obeying a
formula like
• Λ (n,k) = (limit) * ( n2 /n2 – k2)) where
n=k+I, k+2,….
• The Lyman series corresponds to k=1 with
a limit of 91.1 nm, the Balmer series to
k=2 with a limit of 364.5 nm, and so forth