1. Unit 2: Atomic Theory and Periodicity Section 3: Electron Configuration

2. Energy Levels Moving outward from the nucleus, electrons are arranged into energy levels Moving outward from the nucleus, electrons are arranged into energy levels Electrons will completely fill up an energy level before attempting to fill the next level Electrons will completely fill up an energy level before attempting to fill the next level There is a maximum of 7 energy levels which correlate with the 7 periods of the periodic table (currently) There is a maximum of 7 energy levels which correlate with the 7 periods of the periodic table (currently)

3. Sublevels Each energy level is made up of sublevels Each energy level is made up of sublevels There are 4 possible sublevels There are 4 possible sublevels s, p, d, and f s, p, d, and f These sublevels correlate to the major blocks of the periodic table These sublevels correlate to the major blocks of the periodic table The number of elements in that block corresponds to the number of electrons that can fit in that sublevel The number of elements in that block corresponds to the number of electrons that can fit in that sublevel

4. Electron Configuration Since electrons are moving rapidly, but orderly, in the cloud of electrons, we have a way to tell where each electron should be… This is called the electron configuration – the arrangement of the electrons within the sublevels

5. Steps for Electron Configuration Written using the following steps: Written using the following steps: – Find out the # of electrons for the element – Start with 1s and for each sublevel, insert the maximum # of electrons in the exponent position – Continue until each electron has been placed – To check your work, the exponents should should add up to the element’s atomic # (same as the # of electrons)

6. Example: Beryllium Beryllium has 4 electrons… LET’S PLACE THEM! Beryllium has 4 electrons… LET’S PLACE THEM! It is located in Period 2 so its electrons will fill up to the 2 nd energy level Start with 1s and count until you get to Be… 1s 2 2s 2

7. Example: Sulfur Sulfur has 16 electrons… Again, LET’S PLACE THEM! Sulfur has 16 electrons… Again, LET’S PLACE THEM! It is located in Period 3 so its electrons will fill up to the 3 rd energy level Start with 1s and count until you get to Sulfur… 1s 2 2s 2 2p 6 3s 2 3p 4

8. Now, you try! Now, you try!