Quantum Numbers By-N.K.D. Sir Please -Rate review and share this lesson
QUANTUM NUMBERS : In order to define the 'state' of an electron in an atom, a set of four numbers is required known as Quantum numbers. The term 'state' includes, the energy, position with respect to the nucleus, orientation in space and the interaction of the electron with other electrons. (i) Principal Quantum Number (n) : This quantum number was introduced by Bohr. It gives the average distance of the electron from the nucleus. It also indicates the average volume of the electron cloud. It determines the main energy shell in which the electron is revolving round the nucleus. 'n' will have positive integral values only n*0.
The main energy level (shell) corresponding to different values of n are: Principal QuantumMain Energy Number (n) n=1 n=2 n 3 n 4 Level K-shell L- shell M- shell N-shell Energy of electron in n th shell of hydrogen atom and like ions is E =-13.6 eV/ atom where' is the atomic number. As the distance of the electron from the nucleus increases, energy of electron also increases. Energy of electron increases with increasing values of "n".
Energy of electron at infinite distance from the nucleus is zero. Total number of electrons in nth shell is 2n The angular momentum of an electron in an orbit depends upon its principal quantum number and is given by mr- nh where 'n'is principal quantum mumber. (ii) Azimuthal, Angular, Secondary, Subsidiary or Serial Quantum Number () :It was given by Sommerfeld. It explains the fine spectrum of hydrogen atom. It gives the angular momentum of electron in elliptical orbit while in motion round the nucleus. It also gives the shape of the sub-shell in which the electron is located. It () may have any +ve integral value ranging from 0 to (n-1 The total values of I are equal to the Principle quantum number of n Principal Quantum number (n) and azimuthal Quantum number (I) can never have identical numerical values. The orbital angular momentum of an electron depends upon the azimuthal quantum number (l) and is given by: hr Orbital angular momentiun =
3 The total number of subshells (I) in a shell (n) is equal to shell number. The various sub shells corresponding to different values of l, are as follows O Shape Azimuthal Sub Q. Number shell Max. number of electrons Symmetrically spherical shape Dumb-bell Double dumb-bell Complicated shape 2 P- 10 14 ighly complicated 18 shape
The various shells are comprised of the following sub-shells: l-0 s-sub-shell s -0 S-sub-shell 2s (a) - Designation (b) 2, L- shell p-sub- shell 2 p not 2d M-shel 3s l 0 s-sub-shell p-sub- shell 3p- 3d d-sub not3f shell
(d 4 (d) n- 4,N-shell l 0 s-sub-shell p-sub-4 shell -2 3 d-sub- 4d - shell f-sub-shell 4 f Increasing order of energy of subshells is: Decreasing order of screening effect:
Niranjay Kumar Dwivedi
(N.K.D.Sir) is a Complete Chemistry faculty for IIT~JEE, and NEET examination. with more then 8 year of Teaching experience