1. Placement of Electrons & Electron Configuration

2. Electron’s role in reactivity Chemical bonds (when two or more atoms join together) are formed by either the sharing or transferring of electrons Atoms either share electrons with another atom, or they will completely give up electrons to other atoms The number of electrons, and where the electrons are located, determines how reactive the atom is Sodium (Na) has 11 e - and is extremely reactive—it will explode in water Na + has only 10 e - and is found in table salt—not very reactive

3. Electron’s role in reactivity High-energy systems are unstable; unstable systems will lose energy to become more stable Atoms want to be in the most stable arrangement possible They will lose or gain electrons in order to become more stable Electron Configuration is the way electrons are arranged around the nucleus

4. Aufbau Principle Electrons enter orbitals of lowest energy first Aufbau diagram shows the energy levels Orbitals with greater energy are higher on the diagram Which has greater energy, electrons located in the 4d orbital or the 5s orbital?

5. Pauli Exclusion Principle An atomic orbital may describe at most two electrons For any given orbital, there can only be either one or two electrons If there are two electrons in the same orbital, then they must have different spins—one electron spins clockwise while the other spins counterclockwise We represent electrons in orbitals with either an up arrow,, or a down arrow, Different directions of the arrows indicate different spins

6. Hund’s Rule When electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with parallel spins

7. 1 s ___ 2 s ___ p ___ ___ ___ 3 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ 4 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ f ___ ___ ___ ___ ___ ___ ___ 5 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ f ___ ___ ___ ___ ___ ___ ___ 6 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ 7 s ___ p ___ ___ ___

9. How to write an electron configuration 1.Locate the element whose electron configuration you wish to write in the periodic table 2.Fill orbitals in the proper order with electrons 3.Check that the total number of electrons in the electron configuration equals the atomic number

10. Orbital Diagram for Sodium Locate sodium on the periodic table Atomic number is 11, so we also have 11 electrons Fill in each orbital before you can go to the next orbital All the up arrows first and then all the down orbitals 1 s ___ 2 s ___ p ___ ___ ___ 3 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ THIS IS THE ORBITAL DIAGRAM Electron configuration:

11. Orbital Diagram for Sulfur Locate sulfur on the periodic table 16 is the atomic number, so 16 electrons 1 s ___ 2 s ___ p ___ ___ ___ 3 s ___ p ___ ___ ___ d ___ ___ ___ ___ ___ Electron Configuration:

12. Homework Write out the orbital diagram and electron configuration for oxygen (O), phosphorus (P), and calcium (Ca)