There are four types of atomic orbitals:
s, p, d f,
Each orbital can hold a maximum of 2 electrons; one up spin, one down spin.
Three p-orbitals:
. Each can hold two, so the p-orbitals can hold six electrons.
5 d-orbitals: together can hold 10 electrons
7 f-orbtitals (if I remember correctly): can hold 14 electrons
Each electron has a certain energy level, n =1, 2, 3, 4, 5, etc…
To write the electron configuration, you just fill up the orbitals with electrons in the order of s, p, d, f, and energy levels, n =1, 2, 3, 4, etc. For
example, configurations for various number of electrons:
1S1
if there was only one electron for this atom
1S2
two electron atom
1S22s1
3 electrons
1s22s22p1
five electrons
1s22s22p63s1
11 electrons
1s22s22p63s23p64s23d1
21 electrons. The 3d-orbitals fill first for the transition metals, before the 4s
So this indicate you have to know the rules for electron configurations, because there are a few exceptions, which require you to pay attention
in class.
In group 1, we fill starting with 1S1. As we go down the period, it the outer electrons become 2s1, 3s1, 4s1 etc. In group 2, we start with Be which
is 2s2. Go down the period you get 3s2, 4s2.
H
1s1
2A
3
Li
[He]2s1
4
Be
[He]2s2
1s22s1
11
Na
[Ne]3s1
1s22s2
12
Mg
[Ne]3s2
1s22s22p63s1
19
K
[Ar]4s1
20
Ca
[Ar]4s2
1s22s22p63s23p64s1
37
Rb
5s1
38
Sr
5s2
55
Cs
56
Ba
6s1
6s2
87
Fr
7s1
88
Ra
7s2
On the right of the periodic table, we start with the 2s, then fill the p-orbitals.
B
[He]2s22p1
C
[He]2s22p2
N
[He]2s22p3
O
[He]2s22p4
F
[He]2s22p5
1s22s22p1
1s22s22p2
1s22s22p3
1s22s22p4
1s22s22p5
13
Al
[Ne]3s23p1
14
Si
[Ne]3s23p2
15
P
[Ne]3s23p3
16
S
[Ne]3s23p4
17
Cl
[Ne]3s23p5
[Ne]3s23p13d0
31
Ga
4s24p1
1s22s22p63s23p43d0
32
Ge
4s24p2
33
As
4s24p3
34
Se
4s24p4
35
Br
4s24p5
See where we’re going?
For transition metals, it’s the d orbitals that gets filled.
21
Sc
[Ar]4s23d1
22
Ti
[Ar]4s23d2
39
Y
2
5s 4d1
40
Zr
5s24d2
23
24
25
26
27
28
29
30
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
2
3
1
5
2
5
2
6
2
7
2
8
1
10
[Ar]4s 3d [Ar]4s 3d [Ar]4s 3d [Ar]4s 3d [Ar]4s 3d [Ar]4s 3d [Ar]4s 3d
[Ar]4s23d10
41
Nb
5s14d4
42
Mo
5s14d5
43
Tc
5s14d6
44
Ru
5s14d7
45
Rh
5s14d8
46
Pd
4d10
47
Ag
5s14d10
Then you get the rare-earths, which is the f-orbitals.
58
59
Ce
Pr
2 1
1
2 3
6s 4f 5d 6s 4f 5d0
90
91
Th
Pa
2 0
2
2 2
7s 5f 6d 7s 5f 6d1
60
Nd
2 4
6s 4f 5d0
92
U
2 3
7s 5f 6d1
61
Pm
2 5
6s 4f 5d0
93
Np
2 4
7s 5f 6d1
62
Sm
2 6
6s 4f 5d0
94
Pu
2 6
7s 5f 6d0
63
Eu
2 7
6s 4f 5d0
95
Am
2 7
7s 5f 6d0
64
Gd
s2 7
6 4f 5d1
96
Cm
2 7
7s 5f 6d1
65
66
Tb
Dy
2 9
0
2 10
6s 4f 5d 6s 4f 5d0
97
98
Bk
Cf
2 9
0
2 10
7s 5f 6d 7s 5f 6d0
48
Cd
[Kr]5s24d10