Arrangement of Electrons in an Atom

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The arrangement of electrons in an atom is governed by two rules:

(1) Hund’s rule — It states that electrons filling an orbital will first exist singly before pairing.

(2) Pauli exclusion principle — It states that not more than two electrons will occupy an orbital and these two electrons must spin in opposite directions.

Example:

electron arrangement in atom
electron arrangement in atom

Modern Eletronic Configuration

Sub shells No. of orbital Maximum electrons 
S 1 2
P 3 6
D 5 10
F 7 14
ELEMENTS CONFIGURATION NO. OF ELECTRONS
Hydrogen 1S1 1
Helium 1S2 2
Lithium 1S2, 2S1 3
Beryllium 1S2, 2S2 4
Boron 1S2, 2S2, 2P1 5

note: d block elements are transition elements. 4 F are lanthanides while 5 F are actinide elements.

Atomic number is the number of Proton in the nucleus of an atom. Z represents it.

Mass number is the sum of Proton and neutron present in the nucleus of an atom. A represents it.

Others are Viewing:
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  3. Dalton’s Atomic Theory
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  5. Quantum Number
  6. Periodic Table
  7. Periodic Trends

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