2.2.2 Sub-shells and energy levels

2.2.2 Sub-shells and energy levels

1. Sub-shells

   • An e- shell is made up of atomic orbitals with the same principle quantum number, n
   • Within each shell orbitals of the same type are groups together as a sub-shell
     • Each sub-shell is made up of 1 type of atomic orbital only so there are s, p, d and f sub-shells
   • In the figure, each box represents an orbital that can hold up to 2 e- and each shell gains a new type of sub-shell

2. Electron energy levels

   • The sub-shells within a shell have different energy levels

3. Filling shells and sub-shells

   • The electron config. is the arrangement of e- in an atom or ion
   • You can work out the e- config. by using the Aufbau principle
     • The e- in shells of atoms are arranged like:
       • e- are added, one at a time, to build up the atom
       • The lowest available energy level is filled first
       • Each energy level must be full before moving onto the next
     • The sub-shells are made up of several orbitals, each with the same energy level:
       • When a sub-shell is built up with t-. each orbital is filled singly before pairing
       • The 4s orbital is slightly lower energy level that 3d so 4s will fill before 3d

4. Filling the orbitals

   • Orbitals fill from the lowest energy level upwards
   • The 2p orbitals are filled singly before pairing at O
   • Paired e- have opposite spins

5. Electron configuration

   • We use a special shorthand to show electron config.
   • The table shows the electron config for atoms of B, C, N and O
   • For ions:
     • Ions are formed when atoms lose or gain e-
     • If atoms become + ions, e- found in the highest energy level are lost first. The e- config will show fewer e- at the highest energy level
     • For negative ions, e- are added so we continue to fill the sub-shells in the normal way

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