Geology Reference
In-Depth Information
s
l = 0
p
l = 1
d
l = 2
f
l = 3
3rd trans.
series
Lanthanides
6p
5d
4f
6s
2nd trans.
series
Li
Z = 3
Fe
Z = 26
U
Z = 92
5p
4d
-10 0
5s
1st trans.
series
-10 3
4p
-10 0
3d
-10 1
4s
Second
row
3p
-10 2
3s
-10 4
Figure 5.7 A generalized diagram of the
energy-level structure in more complex atoms.
Note that the vertical axis is non-linear (unlike
Figure 5.6), as shown by the scales on the left.
It approximates to an inverted logarithmic
scale. In contrast to Figure 5.6, orbitals sharing
the same value of n no longer share the same
energy, but increase with the value of l as well
(i.e. s < p < d < f).
￿rst row
-10 1
2p
-10 3
2s
d and f orbitals become
progressively more
'stabilized' relative to s
as Z increases across
the period
-10 5
-5 × 10 1
1s
-10 4
next-lowest energy level, 3 s. Here, however, it has a
conspicuously higher energy than the other electrons
in the atom. Because it extends much further from the
nucleus in the 3 s orbital, and requires much less energy
to remove it from the atom altogether, this solo elec-
tron dominates the chemical behaviour of sodium. It is
called the valence electron , because it can be used in
transactions with other atoms, rather like a current
account at the bank.
The electrons occupying the 1 s, 2 s and 2p orbitals of
the sodium atom, on the other hand, are much more
tightly held and they never participate in sodium's
chemical reactions. They comprise what is called the
electron core of the atom, and resemble personal
wealth tied up in stocks and shares, too immobile to be
used in day-to-day transactions.
Because of the way orbitals are grouped in energy
space by their value of n (Figure 5.7), it is sometimes
useful to speak of electron shells . Electrons in the 1 s
state comprise the K shell , those in 2 s and 2p com-
prise the L shell , and so on, as shown in Figure 5.6. In
hydrogen, all orbitals in the same shell have the same
energy, but this is not true of multi-electron atoms
(Figure 5.7). One can likewise speak of valence elec-
trons collectively as the valence shell . One must, how-
ever, be careful in attributing spatial significance to
the term 'shell'. It is useful in suggesting that elec-
trons in the M shell project further from the nucleus
than those in the L shell, but any impression that
electrons are sharply segregated into hollow shells -
as some elementary textbooks suggest - is of course
false.
 
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