1. Electron Configurations 03/28/12

2. N. Bohr 1913 Electrons travel in definite paths. Electrons jump between levels from path to path. Bohr Model of the Atom

3. Electron Energy Levels Any of the several different regions in which electrons travel about the nucleus. As electrons increase in energy, they occupy energy levels farther from the nucleus.

4. Bohr Diagram First energy level is filled with 2 electrons. Second energy level is filled with 8 electrons Third energy level is filled with 18 electrons P + N Nucleus 1 st energy level 2 nd energy level 3 rd energy level

5. Valence electrons Outermost energy level of an atom is called valence shell. Electrons in valence shell are called valence electrons. Group number indicates the number of valence electrons.

6. How do you determine the number of energy levels? Period number determines the number of energy levels. Example: Sodium is in period 3, so it has 3 energy levels

7. Electron configurations Boron – Atomic number 5, Mass number 11 Number of protons = number of electrons = 5

8. Example - Sodium Atomic number = 11, Mass number = 23

9. Example - Calcium Atomic number = 20, Mass number 40

10. Practice