Electronic Configuration

go back

• Electrons are arranged in energy levels or shells

• n is the principal quantum number or shell number

• The maximum number of electrons in each shell is:

  $2n^2$

• Shells are divided into sub shells

  • S: Holds maximum of 2 electrons
  • P: Holds maximum of 6 electrons
  • D: Holds maximum of 10 electrons
  • F: Holds maximum of 14 electrons

Principle Quantum Shell	Sub-shells	Total Number of Electrons
n=1	1s	2
n=2	2s, 2p	8
n=3	3s, 3p, 3d	18
n=4	4s, 4p, 4d, 4f	32

Order of filling of sub-shells

• Rule for fulling sub-shells with electrons is to start with the lowest energy available sub-shell
• The sub-shells can be seen below in increasing order of energy

$1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^{10},4p^6,5s^2,4d^{10},5p^6,4f^{14},6s^2...$

• Orbital: region around the nucleus of an atom that can hold up to 2 electrons with opposite spins
  • Area of space which has a high probability of an electron existing in that area. Up to 2 electrons can exist there, each with an opposite spin

Sub-shell	Shape
S	Sphere
P	Infinity Symbol

• Each orbital holds up to 2 electrons regardless of whether it is an “s”, a “p” or a “d” orbital
• Electrons have opposite spin to prevent repulsion
• The number of occupied energy shells is equal to the period number
• Outermost electron in “x” sub-shell is part of the “x” block, x being an unknown variable

$3s^1$

3: Principle Quantum Number/Principle Sub-shell

s: sub-shell name

1: number of electrons in energy shell