chemistry

QUANTUM NUMBERS AND SIGNIFICANCE

The various orbitals in an atom qualitatively distinguished by their size, shape and orientation.

The atomic orbitals are precisely distinguished by the numbers known as quantum numbers. Each

orbital is designated by three quantum numbers labelled as n, l and m.

There are four quantum numbers required for a complete explanation of electrons in an atom.

The quantum numbers are

1) Principal quantum number (n)

2) Azimuthal quantum number ( l)

3) Magnetic quantum number (m)

4) Spin quantum number (s)

1. Principal Quantum Number (n):

i. It was proposed by Neil’s Bohr

ii. The value of n is 1,2,3,4............. (Or) K, L, M, N............ respectively

iii. As ‘n’ value increases, the size and energy of the orbit also increase.

Iv. The maximum number of electrons possible in an orbit = 2n2

v .The maximum number of orbitals possible in an orbit = 2n

vi. The maximum number of sublevels possible in an orbit =n

vii. The angular momentum of an electron in an orbit i.e. mvr = nh/2_

Significance: It indicates the size and energy of the orbit for hydrogen atom and hydrogen like

species

2.Azimuthal Quantum Number(L):

I . It was proposed by Somerfield

ii. The values of l are 0, 1, 2,..... (n-1), a total of n values.

iii. The value of l represents various sub shells and l = 0,1,2,3 etc... are called s,p,d,f..........

iv. It indicates the orbital angular momentum of electron. Orbital angular momentum of the electron

is given by ( 1)

2

h

l l

p

+

V. It represents the sub shell to which electron belongs.

Significance: It indicates the shape of orbitals S-spherical, P-dumb bell and d- double dumb bell.

3. Magnetic Quantum Number (m):

i. It was proposed by Lande

ii. The values of m are +l to -l including zero, a total of 2l+1 values

iii. The total number of m values indicates the total number of orbitals in the subshell. The number

of orbitals in s, p, d and f sub shells is 1, 3, 5 and 7 respectively

iv. The number of oribitals in a sub shell =2l+1 and electrons = 2(2l+1)

Significance: It indicates the orientation of orbitals in space

4. Spin Quantum Number(S):

i. It was proposed by Goldsmith and Uhlenbeck

ii. The values of S in clock wise direction is represented by + 1/2 and anti clock wise, direction is

represented by - 1/2

iii. An orbital can accommodate maximum of 2 electrons with opposite spin.

iv. The maximum number of electrons accommodated by s, p, d and f subshells is 2,6,10 and 14

respectively.

Significance: It indicates the direction of the spin of the electron