Electron Configurations

 Energy level of an electron analogous to the rungs of a ladder  The electron cannot exist between energy levels, just like you can’t stand between rungs on a ladder

 of energy is the amount of energy required to move an electron from one energy level to another

 derived an equation that described the energy and position of the electrons in an atom

 Has energy levels for electrons.  Orbits are not circular.  It can only tell us the probability of finding an electron a certain distance from the nucleus.

 The atom is found inside a blurry “electron cloud”  An area where there is a chance of finding an electron.  Think of fan blades

atomic orbitals (coined by scientists in 1932) - regions where there is a high probability of finding an electron.  Sublevels- letters s, p, d, and f

Generally symbolized by “n”, it denotes the shell (energy level/period) in which the electron is located. Maximum number of electrons that can fit in an energy level is: 2n 2

s p d f # of shapes (orbitals) Maximum electrons Starts at energy level

 …are the way electrons are arranged in various orbitals around the nuclei of atoms.

1) Aufbau principle - electrons enter the lowest energy first.

2) Pauli Exclusion Principle - at most 2 electrons per orbital - different spins

No two electrons in an atom can have the same four quantum numbers. Wolfgang Pauli To show the different direction of spin, a pair in the same orbital is written as:

3) Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to.  Let’s write the electron configuration for Phosphorus

 The first two electrons go into the 1s orbital Notice the opposite direction of the spins  only 13 more to go... Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p4p 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 5d5d 7p 6d6d 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 7p7p 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 6p6p 3d 4d4d 5d 7p 6d 4f 5f

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d3d 4d 5d 7p7p 6d 4f 5f The last three electrons go into the 3p orbitals. They each go into separate shapes (Hund’s) 3 unpaired electrons Orbital notation

 Let’s stick with P = 1s 2 2s 2 2p 6 3s 2 3p 3 Confused? Don’t be…there is an easy way to write these things based on the positions of elements on the chart First, grab your chart

 Look at the Labels  group 1: s 1  Group 2: s 2  Group 3: p 1  Group 4: p 2  Group 5: p 3  Group 6: p 4  Group 7: p 5  Group 8: p 6  Transition Metals: d 1-10  Lanthanide series f: 1-14

 Now, go back to P  What period is P? 3  What group is P? 5  So, now we build up: 1s 1 (H), 1s 2 (He), 2s 1 (Li), 2s 2 (Be), 2p 1 (B), 2p 2 (C), 2p 3, (N), 2p 4 (O), 2p5 (F), 2p 6 (Ne), 3s 1 (Na), 3s 2 (Mg), 3p 1 (Al), 3p 2 (Si), 3p 3 (P) 1s 2 2s 2 2p 6 3s 2 3p 3

 H  He  Li  Be

BCNOBCNO

 F  Ne