Shape of orbitals
s-orbital
p-orbitals
Electrons can only occupy so-called atomic orbitals with well defined
energy levels corresponding to the principal quantum number, n. The
lowest level will have n = 1, the next n = 2, and so on.
Electrons must always enter the first available orbital of lowest energy.
The first element, hydrogen, only has one electron, and so this electron
must enter the 1s orbital.
The electronic configuration of hydrogen in the ground state must therefore
be: H 1s1.
Boron 1s2 2s2 2p1
Atomic number 5
Carbon 1s2 2s2 2p2
Atomic number 6
According to Hund’s rule, fill a set of similar energy orbitals with as many
unpaired electrons as possible (as in the p or d orbitals).
The successive ionization energies of sodium [Ar] 3s1
•
•
•
•
Electron removed
Ionization
energy/KJmol-1
orbital
1st
496
3s1
2nd
4565
3rd
691
4th
9544
5th
13 352
6th
16 611
7th
20 115
8th
25 491
9th
28 934
10th
141 367
1s2
11th
159 079
1s1
2p6, 2p2
One electron furthest away from nucleus easiest to remove (3S1)
Eight nearer to nucleus, harder to remove (2p6, 2p2)
Two very close to the nucleus and most difficult to remove (1s2)
Proves numbers of electrons in each shell is 2,8,1
First ionisation energies (IE) of elements in
periods 2 to 4/KJmol-1
IEs increase across period (nuclear charge increasing,
shielding the same)
Li,
520
Be,
900
B,
801
C,
1086
N,
1402
O,
1314
F,
1681
Ne,
2081
Na,
495
Mg,
735
Al,
580
Si,
780
P,
1060
S,
1005
Cl,
1255
Ar,
1527
K,
419
Ca,
590
Ga,
579
Ge,
762
As,
947
Se,
941
Br,
1140
Kr,
1351
IEs decrease
down a group
(distance of outer
electrons from
nucleus
increasing)
First ionisation energies (IE) of elements in
periods 2 to 4/KJmol-1
1.
2.
Look at group II and group III: the first electron for Al is a 3P1 electron and is less
tightly held than 3S electron as it is further away from nucleus
Look at group V and group VI: a paired electron is easier to remove than an
unpaired electron and the configuration for sulfur is 3P4, so it has a paired
electron
Li,
520
Be,
900
B,
801
C,
1086
N,
1402
O,
1314
F,
1681
Ne,
2081
Na,
495
Mg,
735
Al,
580
Si,
780
P,
1060
S,
1005
Cl,
1255
Ar,
1527
K,
419
Ca,
590
Ga,
579
Ge,
762
As,
947
Se,
941
Br,
1140
Kr,
1351
The Ionization Energies for elements in Period 3
Element
I1
I2
I3
I4
I5
I6
I7
Na
495
4560
Mg
735
1445
7730
Al
580
1815
2740
11600
Si
780
1575
3220
4350
16100
P
1060
1890
2905
4950
6270
21200
S
1005
2260
3375
4565
6950
8490
27000
[Ne]3S23P4
Cl
1255
2295
3850
5160
6560
9360
11000
[Ne]3S23P5
Ar
1527
2665
3945
5770
7230
8780
12000
[Ne]3S23P6
configuration
[Ne]3S1
[Ne]3S2
I1 = first ionization energy;
A(g)
I2 = second ionization energy; A+(g)
I3 etc.
[Ne]3S23P1
[Ne]3S23P2
A+(g) + eA2+(g) + e-
[Ne]3S23P3