The Foundations of Chemistry

216 CHAPTER 5: The Structure of Atoms

Figure 5-28 The usual order of filling (Aufbau order) of the orbitals of an atom. The

relative energies are different for different elements, but the following main features should

be noted: (1) The largest energy gap is between the 1sand 2sorbitals. (2) The energies of

orbitals are generally closer together at higher energies. (3) The gap between npand (n1)s

(e.g., between 2pand 3sor between 3pand 4s) is fairly large. (4) The gap between (n
1)d

and ns(e.g., between 3dand 4s) is quite small. (5) The gap between (n
2)fand ns(e.g.,

between 4fand 6s) is even smaller.

Figure 5-29 An aid to
remembering the usual order of
filling of atomic orbitals. Write each
shell (value of n) on one horizontal
line, starting with n1 at the
bottom. Write all like subshells
(same
values) in the same vertical
column. Subshells are filled in order
of increasing (n
). When
subshells have the same (n
), the
subshell with the lower nfills first.
To use the diagram, we follow the
diagonal arrows in order, reading
bottom to top.

 = 01 2 3

7 s

6 s

5 s

4 s

3 s

2 s

1 s

6 p

5 p

4 p

3 p

2 p

5 d

4 d

3 d

4 f

Increasing energy

n value

8 s

7 p

6 d

5 f

6 s

5 p

4 d

5 s

4 p

3 d

4 s

3 s 3 p

2 s 2 p

1 s

0123

 value

7 s

6 p

5 d

(^44) f
5
6
7
8
3
2
1
n +  = 8
n +  = 6 n +  = 7
n +  = 4 n +  = 5
n +  = 2 n +  = 3
n +  = 1