Page 17 - PRE-U STPM CHEMISTRY TERM 1

Chemistry Term 1 STPM
5 The first and second ionisation energies correspond to the process:
–1
+
C(g) → C (g) + e ∆H = 1090 kJ mol
2+
C (g) → C (g) ∆H = 2350 kJ mol –1
+
6 The ionisation energy increases with the number of electrons
removed. This is because successive species have ever increasing CHAPTER
proton ratio. This causes the remaining electrons to be more
electron 2
tightly held by the nucleus.
7 The graph shows that there is a gradual increase in the first four Sucessive ionisation energy
ionisation energies. However, there is a very large increase in energy increases because electrons
in removing the fifth electron. are removed from cations
8 This suggests that the first four electrons and the fifth electron of increasing charge.
occupy different energy levels or shells.
9 The ionisation energies of the last two electrons are very large
compared to the first four, suggesting that the last two electrons are
closest to the nucleus in energy level or orbit n = 1, while the first
four electrons are in the outermost energy level or orbit, n = 2.
10 The distribution of the five electrons in the boron atom is:
Orbit, n Principle shell No. of electrons
1 K 2
2 L 3

11 A similar study shows that silicon, Si, has the following
14
electronic distribution.
Orbit, n Principle shell No. of electrons
1 K 2
2 L 8
3 M 4

Quick Check 2.3

1 Use appropriate equations to represent the following ionisation:
(a) the 5th ionisation energy of sodium.
(b) the 12th ionisation energy of aluminium.

2 The following graph shows the successive ionisation energies of an element X.

Ionisation
energy

Order of electrons removed

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02 Chapter 2.indd 47 3/26/18 3:14 PM