Page 18 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM
(a) How many electrons are there in one atom of X?
(b) How many energy levels are filled with electrons?
(c) State the distribution of the electrons in X.
3 Element W is in Group 15 of the Periodic Table. Sketch a graph of successive ionisation
CHAPTER energies for the first 8 electrons.

2
2.2 Atomic Orbitals: s, p and d
2015/P1/Q5

Short-comings of Bohr’s model. 1 Although Bohr’s model can satisfactorily explain the formation
of the line spectrum of hydrogen or one-electron species such as
He and Li . It cannot explain the formation of the line spectra of
+
2+
multielectron atoms.
2 Bohr’s model also cannot explain the appearance of extra lines in
the emission spectra of elements when a magnetic field is applied.
3 Modern theories still embrace the concept of quantised energy
levels but totally reject the circular orbit concept.

Energy Subshell

1 A detailed study of the line spectrum of atoms shows that each
principle shell is further made up of subshells with slightly
different energies.
2 The number of subshells in a principle shell is equal to the
n
quantum number of the shell concerned.
3
Principle shell n No. of subshells
2 First, K 1 1
Second, L 2 2
1
Third, M 3 3
Fourth, N 4 4
Fifth, O 5 5
3 In any one subshell, the level with the lowest energy is assigned the
letter s, followed by p, d and f.
For example,
Energy
Principle shell n No. of subshells Symbol
d
First, K 1 1 1s
p Second, L 2 2 2s, 2p
Third, M 3 3 3s, 3p, 3d
s
Fourth, N 4 4 4s, 4p, 4d, 4f
[In all cases, the s orbital has the lowest energy in each shell.]

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02 Chapter 2.indd 48 3/26/18 3:14 PM