Orbitals
The region in the space around the nucleus where the probability of finding
an electron is maximum is known as an orbital of that electron.
Actually, according to the concepts of wave mechanics (electron behaving as a
wave), the negative charge of the electron is spread around the nucleus which is
referred to as �cloud of negative charge.� The charge density can vary
and it is maximum in particular regions. This region of higher probability of
electron cloud is called as
orbital.
Types of orbitals :
There are four different types of orbitals s, p, d and f which are used to
express the electronic configuration (arrangement of electrons in different
orbitals) of elements. All these have a particular energy and three dimensional
shape.
Quantum numbers :
The state of the electron in the atom is described by its location and energy
level. These states are governed by the laws of quantum mechanics. The numbers
used to identify these states are termed as quantum numbers. They specify the
location and the energy of an electron.
Principle quantum number (symbolized n) :
It gives the main energy level to which the electron belongs. It is related
to the distance of the electron cloud from the nucleus and hence indicates the
size of the electron cloud.
It is represented by integer and letter designation. It can have any integral
from 1 to infinity but only 1 to 7 have been established for known elements.
If n = 1 it corresponds to the lowest energy level and is designated as �K�
level or shell. The subsequent letters L, M, N, ... etc. denote progressive
higher energy levels.
The total number of electrons in the same shell is given by 2n2
Subsidiary or orbital quantum number ( symbolized�l� ) :
It indicates sublevel or subshell in which the electron is present. It also
indicates the shape of the electron cloud.
The values of � l � range from 0 to n-1
|
� l � |
= |
0 |
1 |
2 |
3 |
|
|
|
|
|
|
|
letter designation |
= |
s |
p |
d |
f |
|
shape |
= |
spherical |
dumb-bell |
four-lobe planar |
complicated |
|
No.of orbitals |
= |
1 |
3 |
5 |
7 |
|
Max.no.of electrons |
= |
2 |
6 |
10 |
14 |
The maximum number of electrons each orbital can accommodate is two.
A set of electron orbitals with the same values �n� and �l� is called a
subshell which is represented by the following notation:
Figure 5 subshell notation
Electronic configuration of various atoms are given in following table with
valence subshell.
Table 4
|
Atomic No. |
Element |
Atomic wt. |
Eletronic configuration |
Valence subshell |
Common valences |
|
|
|
n=1 |
n=2 |
n=3 |
|
|
|
1 |
Hydrogen |
1 |
1s1 |
|
|
1s1 |
+1, -1 |
|
2 |
Helium |
4 |
1s2 |
|
|
1s2 |
0 |
|
3 |
Lithium |
7 |
1s2 |
2s1 |
|
2s1 |
|
|
+1 |
|
|
|
|
|
|
|
4 |
Beryllium |
9 |
1s2 |
2s2 |
|
2s2 |
+2 |
|
5 |
Boron |
11 |
1s2 |
2s22p1 |
|
2p1 |
+3 |
|
6 |
Carbon |
12 |
1s2 |
2s22p2 |
|
2p2 |
+4, +2, -4 |
|
7 |
Nitrogen |
14 |
1s2 |
2s22p3 |
|
2p3 |
+5, +3, -3 |
|
8 |
Oxygen |
16 |
1s2 |
2s22p4 |
|
2p4 |
-2 |
|
9 |
Fluorine |
19 |
1s2 |
2s22p5 |
|
2p5 |
-1 |
|
10 |
Neon |
20 |
1s2 |
2s22p6 |
|
2p6 |
0 |
|
11 |
Sodium |
23 |
1s2 |
2s22p6 |
3s1 |
3s1 |
+1 |
|
12 |
Magnesium |
24 |
1s2 |
2s22p6 |
3s2 |
3s2 |
+2 |
|
13 |
Aluminium |
27 |
1s2 |
2s23s2 |
3p1 |
3p1 |
+3 |
|
14 |
Silicon |
28 |
1s2 |
2s22p6 |
3s23p2 |
3p2 |
+4 |
|
15 |
Phosphorous |
31 |
1s2 |
2s22p6 |
3s23p3 |
3p3 |
+5 , +3 , -3 |
|
