• Each shell can be divided further into?subshells, labelled s, p, d and f
• Each subshell can hold a specific number of orbitals:
  • s subshell : 1 orbital
  • p subshell : 3 orbitals labelled px, py?and pz
  • d subshell : 5 orbitals
  • f subshell : 7 orbitals
• Each orbital can hold a maximum number of 2 electrons so the maximum number of electrons in each subshell are as follows:
  • s : 1 x 2 = total of 2 electrons
  • p : 3 x 2 = total of 6 electrons
  • d : 5 x 2 = total of 10 electrons
  • f : 7 x 2 = total of 14 electrons
• In the ground state, orbitals in the same subshell have the same energy and are said to be degenerate, so the energy of a px?orbital is the same as a py?orbital

Shells are divided into subshells which are further divided into orbitals

Summary of the arrangement of electrons in atoms table

• The?principal quantum shells?increase in energy with increasing?principal quantum number
  • E.g.?n?= 4 is higher in energy than?n?= 2
• The?subshells?increase in energy as follows: s ＜ p ＜ d ＜ f
  • The only exception to these rules is the 3d orbital which has slightly higher energy than the 4s orbital
  • Because of this, the 4s orbital is filled before the 3d orbital
• All the orbitals in the?same?subshell have the same energy and are said to be?degenerate
  • E.g. px, py?and pz?are all equal in energy

Relative energies of the shells and subshells

s orbitals

• The s orbitals are?spherical?in shape
• The?size?of the s orbitals increases with increasing shell number
  • E.g. the s orbital of the?third?quantum shell (n?= 3) is bigger than the s orbital of the?first?quantum shell (n?= 1)

The s orbitals become larger with increasing principal quantum number

p orbitals

• The p orbitals are?dumbbell-shaped
• Every shell has three p orbitals except for the first one (n?= 1)
• The p orbitals occupy the x, y and z-axis and point at right angles to each other so are oriented?perpendicular?to one another
• The lobes of the p orbitals become?larger?and?longer?with increasing shell number

The p orbitals become larger and longer with increasing principal quantum number