Electron Configurations

 Using quantum numbers to give the arrangement of electrons around the nucleus.  There are three rules that must be followed!

Rule #1  AUFBAU principle Electrons fill low energy orbitals first Electrons fill low energy orbitals first s,p,d then fs,p,d then f Filling orderFilling order 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p

Rule #2  Pauli Exclusion Principle Since there are two possible spins for an electron, no more than two electrons may fill an orbital. Since there are two possible spins for an electron, no more than two electrons may fill an orbital. Remember: s = 1 orbital, p = 3 orbitals, d = 5 orbitals and f = 7 orbitalsRemember: s = 1 orbital, p = 3 orbitals, d = 5 orbitals and f = 7 orbitals

Rule # 3  Hund’s Rule When multiple shapes are present, electrons fill orbitals with parallel spins before pairing up. When multiple shapes are present, electrons fill orbitals with parallel spins before pairing up. Must follow rule #2!Must follow rule #2! Example 2p Example 2p

Write the following electron configurations 1. Li 2. Na 3. Be 4. C 5. Si

Using the Periodic Table 1. Read from left to right and top to bottom. 2. Stop when you: a. Reach the end of a row b. Change color c. Reach the element of interest 3. Try the following Mg, B, Ne and Cl

Short-Cut  Skip back to the previous Noble Gas (core electrons) and start with the element after that.  Try: I, U, Fe