Atomic Structure: Shells, Sub-Shells & Orbitals

Atomic Structure: Shells, Sub-Shells & Orbitals

1. Rules for filling sub-shells

   • Lowest energy orbitals fill first
     • the entire subshell of a particular orbital type is filled before moving to the next subshell of higher energy.
   • Pauli Exclusion Principle
     • Only two electrons are permitted per orbital and they must be of opposite spin
   • Hund's Rule
     • The most stable arrangement of electrons in a subshell occurs when the maximum number of unpaired electrons exist
   • Singly filled first
     • They will occupy orbitals singly until a sub-shell is half full before they start pairing up

2. The order of sub-shell filling

   • 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

3. Sub-shells and electrons

   • s sub-shells
     • 2 electrons
     • 1 orbital
   • p sub-shells
     • 6 electrons
     • 3 orbitals
   • d sub-shells
     • 10 electrons
     • 5 orbitas

4. Half full sub-shells

   • Chromium
     • 1s2 2s2 2p6 3s2 3p6 3d5 4s1
   • Copper
     • 1s2 2s2 2p6 3s2 3p6 3d10 4s1

5. Principal quantum number

   • n=1,2,3...
     • n=1 : Ground state
   • specifies the energy of an electron and the size of the orbital
     • the distance from the nucleus of the peak in a radial probability distribution plot

6. shapes of orbitals

   • s orbital
     • spherical
   • p orbitals
     • dumb-bell shaped