| Atomic
energy levels |
|
To exactly
explain why we fill such shell structures
and why we can accommodate different
numbers of electrons, a new mechanics,
called quantum mechanics, was developed
to understand the behaviour of atomic
electrons. Quantum mechanics was developed
by many scientists but Schrodinger,
Heisenberg, Plank, Bohr, Pauli, were
some of the major contributors. |
|
To
put it simply, quantum mechanics postulated
that for a given principal quantum number
n, which gave the shell number, there
were sub-shells or orbitals also. The
next quantum number is l, the angular
momentum quantum number. l can take
values from l =0,1,2,... up to (n-1).
The subshells were denoted by letters
l=0 is s sub shell, l=1 is p subshell,
l=2 is d subshell, l=3 is f subshell
and so on. |
|
It
was proposed that an electron has spin
– which can have two directions, up
or down. Pauli suggested that in a given
orbital, only two electrons could be
accommodated – up and down. This is
known as Pauli’s exclusion principle. |
|
The
p subshell could have three or (2l+1)
different orientations, denoted by px,
py, pz. Using Pauli’s exclusion principle,
the p subshell can accommodate 6 electrons. |
| The
d subshell could have five or (2l+1)
different shapes and orientations. |
The
following table summarizes the shells
and subshells structure of an atom.
|
Principal quantum number (n) |
Shell letter |
l values
s p d f |
Number of electrons
in each subshell |
|
1 |
K |
0 |
2 |
|
2 |
L |
0 1 |
2, 6 |
|
3 |
M |
0 1 2 |
2, 6, 10 |
|
4 |
N |
0 1 2 3 |
2, 6, 10, 14 |
|
|
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