The document discusses quantum numbers and their roles in describing electron orbitals. It explains that the principal quantum number (n) determines the size and energy of an orbital, the angular momentum quantum number (l) indicates the shape of an orbital, and the magnetic quantum number (ml) determines the orientation of orbitals in space. It also mentions that the spin quantum number (ms) describes electron spin as either clockwise or counterclockwise.

1. Quantum Numbers © my-chem-tutor.blogspot.com (1) principal quantum no. (n): n = positive integers (1, 2, 3 …) determines size & energy of an orbital. orbitals with the same value of n are said to be in the same quantum shell. no. of orbitals in n th quantum shell = n 2 . (2) angular momentum quantum no. ( l ) : indicates shape of the orbital. can have positive integral values from 0, 1, 2 … (n-1) orbitals having the same values of n & l are said to be in the same subshell . orbitals in the same subshell are degenerate . (3) magnetic quantum no. (m l ) : determines the orientation of the orbitals in space can be any integer from - l to + l no. of possible values (no. of orbitals in a subshell) for m l is (2 l + 1). (4) spin quantum no. (m s ) : electron spin may be clockwise or anti-clockwise. takes values +1/2 or -1/2. f d p s Subshell 3 2 1 0 l

2. Note : one s orbital in each principal shell three p orbitals in the 2 nd & higher shell five d orbitals in the 3 rd & higher shell Prentice Hall © 2005

3. p orbitals s orbital Prentice Hall © 2005

4. d orbitals Prentice Hall © 2005

5. Order of filling orbitals © my-chem-tutor.blogspot.com [1] Fill orbitals with lower energy 1st [Aufbau Principle] [2] Each orbital can accommodate 2 electrons [Pauli Exclusion Principle] [3] Where there is a choice between orbitals of equal energy, fill the orbitals singly 1st [Hund’s Rule] (minimise electron repulsion) 4s orbital is lower in E than 3d ( when unfilled )!

6. Electronic configuration © my-chem-tutor.blogspot.com Examples: Ca O Cl Si Na 20 40 11 23 8 35 16 17 28 14 B 5 11 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 4 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 3s 2 3p 2 1s 2 2s 2 2p 1