Notes on Quantum mechanical model of Atom: It is based on Heisenberg’s uncertainty principle and Schrodinger’s equation. This model helps to understand the electronic structure of an atom more precisely. It explains the address of an electron inside an atom in the form of quantum numbers.
Principle Quantum Number:
It is denoted by “n”. It tells us about the energy and the distance of an electron from the nucleus.
So far we have 7 periods in periodic table hence 7 energy levels can be understood. Each energy level is related to each period.
These shells can also be designated as K L M N O P Q etc.
Azimuthal Quantum Number:
It is denoted by “l”. It’s value depends on Principle Quantum Number n. It tells us about sublevel of a shell that is subshell.
For each value of n, l= 0 to n-1.
So
n=1 means l=0 means “s” subshell
n=2means l=0, 1 means “s” and “p” subshells
n=3 means l=0, 1,2 means “s”, “p” and “d” subshells
n=4 means l=0, 1,2,3 means “s”, “p” , “d” and “f” subshells
n=5 means l=0, 1,2,3,4 means “s”, “p” , “d”, “f” and “g” subshells and so on…….
Magnetic Quantum Number:
It is denoted by “m”. It tells us about the orbitals. Each value of l corresponds to one orbital.
For each value of “l” m= -l to +l on number line.
So l=0 means m=0 means only one value means one orbital.
S subshell has only one orbital.
Spin Quantum Number:
It is denoted by “s” and has two values for each value of m,
+1/2(Clockwise spin) and -1/2(anticlockwise spin) which means two elctrons.
| Principle(n) | Azimuthal(l=0 to n-1) | Magnetic(m=-l,0,+l) | Spin(electron) | |
| 1 | 0 | s | 0 | 2 |
| 2 | 0,1 | s,p | 0,-1,0,+1 | 8 |
| 3 | 0,1,2 | s,p,d | 0,-1,0,1,-2,-1,0,1,2 | 18 |
| 4 | 0,1,2,3 | s,p,d,f | 0,-1,0,1,-2,-1,0,1,2,-3,-2,-1,0,1,2,3 | 32 |
Thus we seen that p subshell start with n=2, d subshell starts with n=3 and f subshell starts with n=4.
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