Page 11 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM
9 The first line in the Lyman series corresponds to n = 1 and n = 2,
2
1
while the second line corresponds to n = 1 and n = 3 and so on.
1 2
10 The same applies to the other series.

Example 2.1 CHAPTER

Calculate the wavelengths and frequencies of the following lines in 2
the emission spectrum of hydrogen.
(a) First line in the Balmer series.
(b) Last line in the Balmer series.

Solution
(a) Using n = 2 and n = 3
1
2
1 = 1.097  10  1 – 
1
7
λ 2 2 3 2
1 = 1.534  10 m –1
6
λ
–7
∴ λ = 6.52  10 m or
= 652 nm
C 3.0 × 10 8
f = = = 4.60 × 10 Hz
14
λ 6.52 × 10 –7
(b) Using n = 2 and n = ∞
1
1
1 = 1.097 × 10  1 – 1 
7
λ 2 2 ∞ 2
1 = 2.74 × 10 m –1
6
λ
∴λ = 3.65  10 m or
–7
= 365 nm
C 3.0 × 10 8
f = = –7 = 8.22  10 Hz
14
λ 3.65 × 10
Bohr's Model of the Hydrogen Atom 2009/P1/Q3

1 In order to explain the formation of the line spectrum of hydrogen, 2014/P1/Q18(a)
Niels Bohr, a Danish physicist, put forward his model of the
hydrogen atom in 1913. [He received the Nobel Prize for physics Bohr's Model of the
in 1922 for his theory explaining the emission line spectrum of Hydrogen Atom
hydrogen]. VIDEO
2 He postulated that electrons revolve round the nucleus in fixed Concept of orbit:
circular paths of different radii called orbits, much like the planets A fixed circular path
revolving around the Sun.
3 The energy of the orbits is quantised. Each orbit is represented by
an integer, n, which is called the principle quantum number.

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02 Chapter 2.indd 41 3/26/18 3:14 PM