Page 33 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM
7 Explain the following observations:
(a) An orbital can accommodate a maximum of only two electrons with opposite spins.
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1
4
2
(b) The electronic configuration of chromium is [Ar]3d 4s instead of [Ar]3d 4s .
8 (a) State Hund’s rule and Pauli’s exclusion principle.
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(b) Draw an energy level diagram showing the electron distribution in an N ion.
2–
9 The number of electrons occupying the different orbitals of atom X is shown in the following table. 2
Orbital s p d
Number of electrons 7 12 10
Write the electronic configuration of X, and explain how each of these orbitals is filled with electrons.

10 (a) The lines in the emission line spectrum of hydrogen are the result of electronic transitions.
(i) Draw an energy level diagram to show the transitions that give rise to the first and last lines in both
the Lyman series and the Balmer series and state in which part of the electromagnetic spectrum that
each of the series belongs to.
(ii) The energy difference between two of the levels in the hydrogen atom is 987.3 kJ mol . Calculate
–1
the frequency and the wavelength of the line produced when electronic transition occurs between
these two levels.
[h = 6.63 × 10 Js; C = 3.00 × 10 ms ; L = 6.02 × 10 mol ]
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–1
–1
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23
(b) An atom X has 24 electrons in its nucleus.
(i) Draw an energy diagram to show how the electrons are arranged in its atom.
(ii) Explain any abnormality in the electronic arrangement.

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02 Chapter 2.indd 63 3/26/18 3:14 PM