What are electron configurations? The way electrons are arranged in atoms. Used to indicate which orbitals (energy levels) are occupied by electrons for a particular atom The letters s, p, d and f are used to identify sublevels; they represent shapes

Remember! Each sublevel orbital holds only 2 electrons but sublevels contain different number of orbitals s – 1 orbital (maximum 2 e - ) p – 3 orbitals (maximum 6 e - ) d – 5 orbitals (maximum 10 e - ) f – 7orbitals (maximum 14 e - )

Energy Levels Different energy levels contain only certain sublevels Energy level 1 – s sublevel only Energy level 2 – s, p sublevel only Energy level 3 – s, p, d sublevel only Energy level 4 – s, p, d, f sublevel only

Some rules! Aufbau Principle - each electrons is added to the lowest orbital available This causes difficulties because of the overlap of orbitals of different energies. Pauli Exclusion Principle - at most 2 electrons per orbital - different spins Hund’s Rule - When electrons occupy orbitals of equal energy they don’t pair up until they have to.

Electron Configurations First Energy Level only s sublevel (1 s orbital) only 2 electrons 1s 2 Second Energy Level s and p sublevels (s and p orbitals are available) 2 in s, 6 in p 2s 2 2p 6 8 total electrons

Third energy level s, p, and d orbitals 2 in s, 6 in p, and 10 in d 3s 2 3p 6 3d total electrons Fourth energy level s,p,d, and f orbitals 2 in s, 6 in p, 10 in d, and 14 in f 4s 2 4p 6 4d 10 4f total electrons

So….. The electrons fill in the following order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f Energy Level Diagram

Try it! Let’s determine the electron configuration for Phosphorus Need to account for 15 electrons

The first to electrons go into the 1s orbital Notice the opposite spins only 13 more Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

The next electrons go into the 2s orbital only 11 more Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

The next electrons go into the 2p orbital only 5 more Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

The next electrons go into the 3s orbital only 3 more Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f The last three electrons go into the 3p orbitals. They each go into separate shapes 3 unpaired electrons 1s 2 2s 2 2p 6 3s 2 3p 3

Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the energy of the orbital. Half filled orbitals have a lower energy, which makes them more stable. Changes the filling order

Write these electron configurations Magnesium – 12 electrons 1s 2 2s 2 2p 6 3s 2 Titanium - 22 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 Vanadium - 23 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3

Transition Metals are special! Draw an energy level diagram and the electronic configuration for: Chromium - 24 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 is expected But this is wrong!!

Chromium is actually 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 Why? This gives us two half filled orbitals. Slightly lower in energy. The same principal applies to copper.

Try it! Copper has 29 electrons

Copper’s electron configuration Copper has 29 electrons so we expect 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 But the actual configuration is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 This gives one filled orbital and one half filled orbital. Remember these exceptions