2.2.1 Shells and orbitals

2.2.1 Shells and orbitals

1. Energy levels or shells

   • e- orbit the nucleus
   • e- aren't free to go wherever the like but they exist as certain energy levels or shells
   • Quantum numbers are used to describe the e- in atoms:
     • The principal quantum number, n, indicates the shell e- occupy
     • Different shells have different principal quantum numbers
     • The larger the value of n, the further the shell is from the nucleus and the higher the energy level
   • Each shell holds up to 2n2 e-

2. Atomic orbitals

   • It is now thought that each shell is made up of a n. of atomic orbitals
   • Each atomic orbital can hold a max of 2 e- with opposite spins
   • An orbital is a region of space where e- may be found
   • There are 4 types of orbital - s, p, d and f - each with a different shape

3. S-orbitals

   • An s-orbital has a spherical shape
   • From n=1 upwards, each shell contains 1 s-orbital
   • It gives a total of 1 x 2= 2s e- in each shell

4. P-orbitals

   • A p-orbital has a 3D dumb-bell shape
   • From n=2 upwards each shell contains 3 p-orbitals
   • It gives a total of 3 x 2 = 6p e-

5. D-orbitals and f-orbitals

   • From n=3 upwards each shell contains 5 d-orbitals which gives a possible total of 5 x 2= 10d e-
   • From n=4 upwards, each shell contains 7 f-orbitals which gives a possible total of 7 x 2= 14f e-

6. Representing e- in orbitals

   • Orbitals have different types and shapes so chemists use box diagrams to represent e- in orbitals
   • Each box represents an individual orbital so they each can hold up to 2 e-
   • The representation is called electrons in boxes
   • Each e- has a - charge so we would expect the 2 e- to repel but it doesn't happen. An e- has a property called spin so the 2 e- in an orbital must have opposite spins
   • In some ways an e- behaves like a particle but in others it behaves like a wave

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