Rules For Filling Of Electrons In Various Orbitals

The atom is built up by filling electrons in various orbitals according to the following rules.

Aufbau Principle

This principle states that the electrons are added one by one to the various orbitals in order of their increasing energy starting with the orbital of lowest energy. The increasing order of energy of various orbitals is

1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,5f,6d,7p……………………

How to remember such a big sequence?

To make it simple we are giving you the method to write the increasing order of the orbitals. Starting from the top, the direction of the arrows gives the order of filling of orbitals.

(n +λ) Rule

Alternatively, the order of increasing energy of the various orbitals can be calculated on the basis of (n +λ) rule.

The energy of an orbital depends upon the sum of values of the principal quantum number (n) and the azimuthal quantum number (λ). This is called (n +λ) rule. According to this rule,

“In neutral isolated atom, the lower the value of (n+λ) for an orbital, lower will be its energy. However, if the two different types of orbitals have the same value of (n +λ), the orbitals with lower value of n has lower energy’’.

Illustration of (n +λ) rule

Electronic Configuration of the Elements

ELEMENTS SYMBOL AT. NO. ELECTRONIC CONFIGURATION

Hydrogen H 1 1s1

Helium He 2 1s2

Lithium Li 3 1s2 , 2s1

Beryllium Be 4 1s2 , 2s2

Boron B 5 1s2 , 2s2 2p1

Carbon C 6 1s2 , 2s2 2p2

Nitrogen N 7 1s2 , 2s2 2p3

Oxygen O 8 1s2 , 2s2 2p4

Fluorine F 9 1s2 , 2s2 2p5

Neon Ne 10 1s2 , 2s2 2p6

Sodium Na 11 1s2 , 2s2 2p6, 3s1

Magnesium Mg 12 1s2, 2s2 2p6, 3s2

Aluminium Al 13 1s2, 2s2 2p6, 3s2 3p1

Silicon Si 14 1s2, 2s2 2p6, 3s2 3p2

Phosphorus P 15 1s2, 2s2 2p6, 3s2 3p3

Sulphur S 16 1s2, 2s2 2p6, 3s2 3p4

Chlorine Cl 17 1s2, 2s2 2p6, 3s2 3p5

Argon Ar 18 1s2, 2s2 2p6, 3s2 3p6

Potassium K 19 1s2, 2s2 2p6, 3s2 3p6, 4s1

Calcium Ca 20 1s2, 2s2 2p6, 3s2 3p6, 4s2

Scandium Sc 21 1s2, 2s2 2p6, 3s2 3p6 3d1 , 4s2

Titanium Ti 22 1s2, 2s2 2p6, 3s2 3p6 3d2 , 4s2

Vanadium V 23 1s2, 2s2 2p6, 3s2 3p6 3d3 , 4s2

Chromium Cr 24 1s2, 2s2 2p6, 3s2 3p6 3d5 , 4s1

Manganese Mn 25 1s2, 2s2 2p6, 3s2 3p6 3d5 , 4s2

Iron Fe 26 1s2, 2s2 2p6, 3s2 3p6 3d6 , 4s2

Cobalt Co 27 1s2, 2s2 2p6, 3s2 3p6 3d7 , 4s2

Nickel Ni 28 1s2, 2s2 2p6, 3s2 3p6 3d8 , 4s2

Copper Cu 29 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s1

Zinc Zn 30 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s2

Gallium Ga 31 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p1

Germanium Ge 32 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p2

Arsenic As 33 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p3

Selenium Se 34 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p4

Bromine Br 35 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p5

Krypton Kr 36 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p6

Rubidium Rb 37 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s14p65s1

Strontium Sr 38 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s1

Ytterium Y 39 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s24d1

Ziroconium Zr 40 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d2

Niobium Nb 41 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d4

Molybdnum Mo 42 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d5

Technecium Tc 43 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d5

Ruthenium Ru 44 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d7

Rhodium Rh 45 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d8

Palladium Pd 46 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d10

Silver Ag 47 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s14d10

Cadmium Cd 48 1s2, 2s2 2p6, 3s2 3p6 3d10 , 4s24p65s24d10

Indium In 49 1s2,2s2,2p6,3s2,3p6,3d10,4s24p65s24d105p1

Tin Sn 50 1s2,2s22p6, 3s2 3p6 3d10 ,4s24p65s24d105p2

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